July 2008 Archives

Menacing thunderstorms rolled into Chicago on Thursday afternoon, blasting the area
with winds up to 70 m.p.h., hail and blinding, flooding rains. Winds reached 70 m.p.h.
at Gary, 62 m.p.h. at West Dundee and 60 m.p.h. at Addison, downing trees and power
lines as the towering 46,000-foot thunderheads swept through. Before striking
Chicago, the storms, which developed Wednesday evening in far southeast
Saskatchewan, produced a corridor of damage across the Dakotas, Minnesota and
northeast Iowa, with unconfirmed reports of winds as high as 115 m.p.h. Before the
storms struck Chicago, Midway recorded its seventh 90-degree reading of the year,
while O'Hare topped out at a steamy 89.

AUGUST, CHICAGO'S WETTEST MONTH, GETS UNDER WAY

August begins Friday and is currently Chicago's wettest month, with a normal rainfall of
4.62 inches. The last month of meteorological summer, August starts the slow
seasonal decline toward autumn. Average high temperatures drop from 83 on the 1st to
78 by the end of the month, and we also lose 1 hour and 14 minutes of daylight.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,

My grandson is eight years old and has a terrible fear of the weather. Is there something
we should do or someone we can contact?
Judi
Dear Judi,

The violent aspects of weather can be especially frightening to children. Here are a few
tips to deal with your grandson's excessive fears:
- Communicate with him; don't deny his fears, but explain that storms are natural
events and you and he can take steps to thwart the threats they pose.
- Explain that he will be safe indoors. Coming inside when rough
weather threatens is a simple yet effective action.
- Research coping techniques. Many web sites contain useful information prepared by
professionals, and help books are available from libraries.
- Finally, consultation with professionals might be warranted if your grandson's
excessive fears cannot be overcome.

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Thursday, July 31, 2008.

Tonight, there was some severe weather in the Western suburbs. Tom gives you an update on that situation and tells you what to expect for this weekend. Stay tuned and check back with Before the Forecast again tomorrow for updates.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Thanks to Dr. Walker Ashley , meteorology professor at Northern Illinois University snapped these pictures as a long-lived derecho with origins in North Dakota and southeast Saskatchewan moved thorugh the DeKalb area early Thursday afternoon.

Photos by Dr. Walker Ashley NIU Meteorology Department

Thanks to Chris Wolff who captured this dramatic shot as thunderstorms swept across Pistake Lake in McHenry around 2 p.m. this afternoon.

Photo by Christopher Wolff

Thanks to Jacob Shipley from Yorkville and Chuck Hagen from Oak lawn for sending us these timely pictures as severe thunderstorms swept through the Chicago area Thursday afternoon.

Storm over Yorkville

Photo by Jacob Shipley

Storm over Argo, Illinois

Photo by Chuck Hagen

Wind damage, rain, and even some hail in certain areas ... this is your Severe Weather Update!

Tom Skilling is tracking the powerful thunderstorms that have been sweeping across the Chicago area, with wind gusts of up to 62 miles per hour. The WGN Weather Center has received recent reports of damage from the storm in the Western suburbs, including wind damage, rain, and even some hail!

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

While much of the Chicago area dodged Wednesday's south suburban t-storms, rains
came down hard in a narrow corridor extending from Kendall and Grundy Counties east
into northern Indiana. Cottony cumulus clouds bubbled aloft to heights of 42,000 feet
and Doppler radar rain estimates ranged up to 2 inches. Rainfall gauges measured 0.44
inches at New Lenox and 0.20 inches at Frankfort. The downpours responsible were
accompanied there by frequent lightning.

The summer rains hit in a July about to close with more sunshine than any of the last
eight months. It's the first month with above-normal sun since November. Chicago
weather observer Frank Wachowski reports 77 percent of the month's possible sun -- a
total of 20,653 minutes out of a possible 26,775 is now on the books.

Wednesday's 90-degree high was the site's sixth reading to hit 90 degrees this year.
Thermometers at Alsip hit 93 degrees, 91 degrees at Palatine and 93 degrees at
Janesville, Wis.

MISSOURI SOAKED BY HURRICANE DOLLY'S REMNANTS WEDNESDAY

Sections of Missouri were swamped by remnants of Hurricane Dolly Wednesday. Totals
included 3.05 inches at Lees Summit, 2.78 at Kansas City and 1.63 at St. Louis.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I remember a very stormy period a few summers ago marked by a lot of hail. What
summer was that?

Marge Wallace

Dear Marge,
It was five years ago during July and August of 2003 that Chicago was bombarded with
hail. Waves of severe thunderstorms swept the area on 16 days between July 4 and
Aug. 3. Some communities were hit with hail on five or six days.

The hail was large, ranging from penny size (3/4-inch) to tennis ball (2.5 inches,) and the
extensive damage was estimated in excess of $90 million. Automobiles and rooftops
took the brunt of the damage, but trees also were stripped of their leaves and gardens
flattened.

Damaging wind and torrential rainfall also accompanied the thunderstorms. The storms
on Aug. 3 brought as much as 4 inches of rain to Chicago's Northwest Side, flooding
streets and viaducts and shutting down the Kennedy Expressway.

Snapshot of the towering Wednesday afternoon cumulonimbus--one of a group which doused south suburban areas with lightning-peppered downpours

Walt Stagner of southwest suburban Yorkville, Illinois sends us this terrific shot of the towering cumulonimbi (thunderheads) responsible for thundery downpours which erupted across many of Chicago's south and southwest suburbs. Doppler radar scans put cloud tops at up to 42,000 ft.
Thanks Walt for the great shot!

Tom Skilling

Photo courtesy of Walt Stagner, Yorkville, Illinois

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Tuesday, July 29, 2008.

Earlier today, the South Suburban areas were hit by thunderstorms, and more storms may be coming our way by Thursday. Next week you can expect real heat and hot air mass to come to town on Tuesday.

Stay tuned and check back with Before the Forecast again tomorrow for updates.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

The heavens opened across a large swath of Illinois late Tuesday, unleashing
downpours that drenched western Illinois' Rock Island with 2 inches of rain. The
Chicago area -- needing rain -- didn't completely escape the thundery deluges. Late
evening Doppler radar scans tracked downpour-generating cloud towers that reached
heights of 41,000 feet.

Even taller Downstate storms, responsible for rainfall so heavy that flash-flood
warnings were necessary in Champaign County and for tree-limb-downing 65 m.p.h.
wind gusts across sections of LaSalle County, were scanned as high as 58,000 feet.

The storms originated in Kansas early Tuesday then swept into Missouri, where they
inundated an area near Memphis, Mo., in the northeast corner of the state, with 1.90
inches in just 30 minutes.

CHICAGO AREA FLIRTS WITH 90 DEGREES WHILE TRIPLE-DIGIT HEAT KEEPS THE SOUTH BROILING

Temperatures hit 89 degrees at Midway Tuesday but 90s weren't far away. Heat in the
Deep South and southern Plains included triple-digit highs -- among them 101
degrees at Memphis and 100 degrees at Little Rock, Ark.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Nevada!?!? I thought Arizona was the driest state with 7.5 inches of rain annually.

Elise White Pearce
Dear Elise,
You are referring to our statement on July 21 that, "Nevada, with a scant 9 inches [of
rain] annually, is the driest [state]."

The annual total (7.5 inches) that you suggested for Arizona is representative only of
central Arizona. Other areas of the Grand Canyon State, especially the higher elevations
of the north, receive up to 22 inches. The state as a whole gets 14 inches.

Nevada lies in the "rain shadow" of the Sierra Nevada Mountains to its west and it is
sheltered from precipitation accompanying storms from the Pacific Ocean.

In addition, Arizona experiences a summer monsoon when thunderstorm-triggering
moisture from the Gulf of California, just to the south, works its way across the state.
Nevada, farther northwest, receives little of that moisture.

Thanks to frequent contributor Dan Hanson of Winter, Wisconsin for this dramatic picture of a
sunlight cumulonimbus cloud taken last Friday evening July 25th.

Photo by Dan Hanson

Steve Kahn WGN Weather Center Meteorologist

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Tuesday, July 29, 2008.

Get inside the WGN Weather Center as Tom shows you what he is looking at for the upcoming week. Today, there was some minor cooling from the lake effect along the shoreline, but there are building storms along the southern region that may affect Chicago-land this weekend. This has caused the humidity in Suburban areas to begin to build.

Stay tuned and check back with Before the Forecast tomorrow for updates.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Julie Pavletich was on her morning ride in suburban Busse Woods bike trail around 5:50
a.m. Monday morning (July 28) when she came upon this scene and photographed it.
Julie explains:

" This is exactly how it looked - the fog over the ground, and the sun just poking out
over the trees in the distance."

It's a great photograph, Julie. Thanks for sharing it with us!

Tom Skilling

Photo courtesy of Julie Pavletich, Elk Grove Village

The Chicago area is getting a bit dry, something that doesn't take long to happen this
time of year. Strong summer sunlight encourages the evaporation of the equivalent of
1.20 to 1.40 inches of moisture a week from plants and topsoils. This makes it
essential that rains fall regularly.
But, the big rains of late spring and early summer have exited. The last big rain to fall in
the immediate Chicago area occurred 10 days ago when 1.61 inches fell at O'Hare
Airport and 1.05 inches at Midway Airport. Though scattered thunderstorms may
produce isolated downpours Tuesday, coverage is likely to be limited.
The Southern Plains are being scorched by 105- to 110-degree temperatures. The high
at Wichita Falls, Texas, hit 110 degrees Monday while Dallas tied its record high of 105
degrees.

727 DAYS SINCE LAST 95-DEGREE-PLUS
It's been 727 days since Chicago's last 95-degree-plus reading, a steamy high of 97 on
Aug. 2, 2006. That long stretch could end this weekend if readings reach the mid-90s.

SOME POSITIVE BENEFITS OF DOLLY
Though Hurricane Dolly brought flooding and devastation to South Texas, it also
dumped a welcome 5 inches of rain on some Texas drought areas.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
What is the proper placement for the sensor element for a wireless
thermometer? Mine, located on the house above the patio, reads much hotter
than the reported temperature. Is there a general rule to follow when
selecting a location?
Fred Kloster, Naperville
Dear Fred,
Proper thermometer placement is not easily accomplished in an urban
environment.
The temperature-sensing element must be protected from exposure to direct
sunlight, from precipitation (like rain) and from condensation (like dew),
while at the same time be given adequate ventilation. It must also be
located well away from mechanical heat sources (such as air conditioners)
and from concrete surfaces that are warmed by sunlight.
Ideally, the sensor is best placed in a wooden instrument shelter with
louvered sides, painted white, four feet off the ground, over grass.

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Monday, July 28, 2008.

Get inside the WGN Weather Center as Tom shows you what he is looking at for the upcoming week. So far, he predicts an upcoming 90 degree weather streak for this weekend.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

It's a pattern that has been repeated here all summer. Every time hot weather attempts to
make an inroad into the Chicago area, debris cloudiness or cooling outflows from
thunderstorms keep temperatures down here.
Once again hot weather is headed east into the Midwest as brisk southwest winds are
slated to sweep into the city Tuesday.
The approaching air mass has produced 90s and 100s in the Plains and lower Mississippi
Valley in recent days, such as the 103-degree record-tying high Sunday at Shreveport, La.
Some recent computer model runs have pegged Tuesday's maximum temperature here
in the upper 90s, but values that high seem unlikely as a combination of leftover
cloudiness and rain-cooled air from overnight thunderstorms slow the warm-up.
TYPHOON FUNG WONG MAY DROP 3 FEET OF RAIN ON TAIWAN
Packing winds as high at 105 m.p.h., Typhoon Fung Wong made landfall on the
east-central Taiwan coast Sunday morning.
The storm is expected to bring as much as 36 inches of rain to the central part of the
island with up to 18 inches on its north and south ends, including the capital of Taipei.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
Are the weather events described in the book "Devil in the White City"
correct? Did a funnel cloud really blow through the Midway?
Michael Maher, Arlington Heights
Dear Michael,
Author Erik Larson described the weather conditions during Chicago's 1893
Columbian Exposition correctly; there was indeed a "Funnel in the White
City."
The storm took place the evening of July 9. A sunny, warm afternoon with
scarcely a breeze turned dark as night as a fast-moving squall approached
from the north. The storm brought strong northwest winds that did
considerable damage to the fairgrounds blowing out windows in Jackson Park.
A funnel-shaped cloud destroyed a large hot-air balloon that was tethered to
the ground. Yachts capsized on Lake Michigan, drowning at least four. The
storm dumped 0.42 inches of rain in less than an hour. Peak wind gusts were
not available because the Weather Bureau's wind equipment was damaged during
the storm.

The last week of July in Chicago will certainly be summery -- with daily highs mainly in
the 80s and moderate levels of humidity along with some scattered showers and
thunderstorms -- but lacking the heat, as has been the case nearly all summer.
Nineties have been scarce in Chicago so far this year, with the tally of only three days
at O'Hare International Airport and five at Midway Airport to date -- far below the
typical 15 or 16 usually logged here by the end of July. Another one is possible on
Tuesday.
Hot weather remains anchored from the lower Mississippi Valley to the Southwest
where readings are reaching triple-digits daily. A variety of heat warnings and
advisories are posted for Sunday from Mississippi west to Texas and Oklahoma.
ATLANTIC BASIN QUIET FOR THE MOMENT
After a flurry of activity last week with Hurricane Dolly hitting far south Texas and
Tropical Storm Cristobal skirting the Northeast coast, the Atlantic Basin is currently
storm-free.
However, a well-defined area of disturbed weather about 800 miles east of the Leeward
Islands is moving to the northwest and could develop into Edouard, the season's fifth
named tropical cyclone, later in the week.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
I was surprised to read that a tornado occurred in the mountains of Colorado
last May. Is there any place in the continental U.S. where tornadoes do not
occur?
Tim Rasmussen
Dear Tim,
Tornadoes have occurred in every U.S. state including Alaska and Hawaii, but
of course they are much more common in portions of the Plains, Midwest and
South in the area known as Tornado Alley. Twisters occur with a much lower
frequency in the West, especially in the chilly coastal region of the
Pacific Northwest. Mountain tornadoes have been documented as high as the
12,000-foot level in California's Sequoia National Park. Roger Edwards of
NOAA's Storm Prediction Center notes that the most violent high-altitude
twister was an F3 storm that struck at the 11,000-foot level in Utah's Unita
Mountains on Aug. 11, 1993. Many meteorologists feel that the number of
mountain twisters is under-reported, going undetected in the remote areas of
mountainous West.

Lake Michigan's water level has risen 8 inches above the same period a year ago. Once
just 6 to 12 inches above all-time lows, lake levels are up in response to the same
downpours that caused many area rivers to flood. The U.S. Army Corps of Engineers,
which monitors the Great Lakes, predicts the higher levels are to hold through the
coming months -- though, barring new waves of heavy rains, the biggest rises have
probably already occurred. Interconnected Lakes Michigan and Huron are unlikely to
change significantly in the next month.
The corps reports other Great Lakes have experienced increased levels as well, with
Lake Superior 16 inches higher than a year ago. The rise in Lake Michigan means the
lake has added approximately 3.12 trillion gallons since a year ago.
Blistering heat continues to grip the southern Plains. The heat has anchored northwest
jet-stream winds over the area, which have slowed the eastward expansion of hot air in
recent months.
ABNORMALLY COOL ALASKAN SUMMER: ANCHORAGE'S 6TH-CHILLIEST SINCE 1917
So far this year, Anchorage has seen only seven days where the temperature
reached 65 degrees. Their coolest summer on record (1970) recorded a total of 16 such
days.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
You are always telling us how high the thunderstorm tops are. What is the
highest top ever recorded in the Chicago area and in the world?
Bill Matthews, Schaumburg
Dear Bill,
As a general rule of thumb, the higher the thunderstorm top the more severe
the thunderstorm is likely to be. Storms with the highest tops tend to form
in areas of greatest lift where the atmosphere is most volatile. In the
Chicago area, garden-variety summer thunderstorms develop to heights between
35,000-45,000 feet, but the tops of severe thunderstorms here can approach
60,000 feet and in extreme cases 70,000 feet. The top of the thunderstorm
that produced the Plainfield tornado on Aug. 28, 1990, towered to 65,000
feet. The tallest thunderstorms on Earth have been documented in the tropics
where tops have been measured to about 75,000 feet, building more than 14
miles up into the atmosphere.

These summertime cumulus clouds were photographed by our friend Anson
Mount. Anson is a pilot and snapped this Thursday at the 7,000-foot
level over central Wisconsin. Thanks Anson!

Photo courtesy of Anson Mount

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Friday, July 25, 2008.

In this episode, Tom tells us about the snow they are having right now in Alaska.

Its been an interesting week with Hurricane Dolly coming out of the Gulf of Texas. In Chicago, the lack of fairly hot weather continues for the summer. We can also expect 1-2 inches of rain this weekend in Northern Illinois.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Take a look at this image shot on a remote camera operated by SRI International under
a grant from the National Science Foundation in northern Alaska's western Brooks
Range! That's snow in the photo shown covering the ground this past Monday (July 21)
this week. It was called to our attention by Mark Vogan who was forwarded the image
by Fairbanks, Alaska National Weather Service Lead Forecaster Rick Thoman. Rick
shares this assessment of the snowfall pictured here:

Photo courtesy of SRI International and the National Science Foundation

"Looks like we've made the transition to late summer here, with cooler temps and more
clouds and stratiform rain. Cold pool of air over NW Alaska has produced some snow in
the western Brooks Range. Attached is a pix from this (Monday) morning at Ivotuk
(elevation about 1,8000 feet MSL."

"Accumulating snow at 1,800' elevation on the north side of the Brooks Range in July is
not especially unusual; it does not happen every July, but is by no means unheard of.
There are of course no long term climate sites in the this part of the world; Ivotuk is
100 miles (or so) from the nearest community."

Thanks Rick and Mark!

One note: Subsequent pictures from the site indicate the snow has melted. It's a little
early to keep snow on the ground even at this elevation and latitude.

Photo courtesy of SRI International and the National Science Foundation

Rick points out summer has returned for the time being at the same location. Above is
Friday's image from the same location.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

The country's most humid air sits over a large swath of the Midwest on Friday -- more
humid over sections of the Heartland than the perennially muggy Gulf Coast. That's not
an accident. The Midwest is home to much of this country's most productive cropland
and crops send moisture airborne through a process known as transpiration -- the
evaporation of water from the leaves of plants. Strolling by a mature cornfield, you'll
feel a surge of moisture. Dew points, the preferred measure of moisture among
meteorologists, are expected to reach the 70s later Friday in Chicago and could surge
to near 80 degrees in sections of Missouri and Iowa -- a level most often associated
with tropical rain forests.

Truly hot weather continues to be a surprisingly rare commodity this summer in
Chicago. The highest temperature to occur has been 91 degrees. Not a single summer
in the past 80 years (since 1928) has failed to produce a higher temperature.

DOLLY'S TORNADO-PRODUCTION SPARSE BUT ITS RAINFALL HAS BEEN PLENTIFUL

The remnants of Hurricane Dolly managed only two twisters Thursday -- surprisingly
few for a landfalling Gulf Coast tropical cyclone. However, rains have been prolific.
Laguna Madre, Texas, was hit by more than 16 inches of rain.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I was planning on having lightning rods installed on my house to ward off lightning,
but someone told me they attract lightning. Now I'm having second thoughts. What is
the real story?

Ron White

Dear Ron,
Lightning rod protection is a wise investment.

It is commonly believed lightning rods will prevent a lightning strike by discharging the
overhead thundercloud or by deflecting the bolt. Both thoughts are incorrect. A
lightning rod protects the structure on which it is mounted by attracting to itself
the descending lightning bolt and then conducting its electric charge harmlessly into
the ground via a suitable wire system.

A downward-striking bolt is not affected by surface-based objects like buildings until
it is within less than 300 feet of them, and only then will it usually, but not always,
strike the highest object.

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Thursday, July 24, 2008.

Today, we had a very pleasant 82 degree high as we continue the comfortable temperatures in the Chicago area. Tom is predicting some hot, humid, and muggy weather for this week.

Stay tuned, because the hottest temperatures may still be on the way in late July!

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Hurricane Dolly, after days of ingesting humid, energy-rich Gulf air over bathtub warm
waters, roared onto South Padre Island in Texas with 100 m.p.h. winds at 1 p.m.
Wednesday. In so doing, it became the first hurricane to make landfall on the U.S.
mainland since Hurricane Humberto moved ashore on the Texas/Louisiana border Sept.
13, 2007. Dolly pounded south Texas with rain in amounts that reached 12.85 inches at
Harlingen by nightfall Wednesday. The storm's 80 m.p.h. gusts whipped Padre Island,
transforming adjacent Gulf waters into an angry caldron and producing extensive
damage from the area's beaches to the inland community of Raymondville. Rainfall at
Brownsville topped a half-foot making it the wettest July on record. Concern turned to
the potential for serious inland flooding as the storm moved deeper into the Texas Hill
Country.

SHIFTS IN LONGER RANGE COMPUTER RAIN FORECASTS BEING MONITORED

Earlier forecasts play up dry weather for Chicago, but the latest longer-range forecasts
are hinting at a shift to wetter weather here that could begin as early as late Sunday
with another round of precipitation next week.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I read the article about rip currents in the Sunday Chicago Tribune. Is this the same as
what we used to call "undertow" when I was a kid?

Judith Allen, Chicago

Dear Judith,

Rip currents and undertow are two entirely different water transport features that occur
in the shore area of oceans and large lakes like Lake Michigan. Both move water
brought to the shore by waves back into the lake (or ocean).

A rip current, flowing at speeds up to 4 m.p.h., is a surface flow of water, usually 20 to
100 feet in width, flowing outward from the shore. It won't pull a swimmer beneath the
waves, but it can carry him a few hundred feet out. It's literally a "river in the lake."

Unlike the powerful, localized and dangerous surface rip current, undertow is a brisk
bottom flow in shallow water (2-4 feet deep). It transports water carried onto the beach
by breaking waves, and is a lesser threat.

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Tuesday, July 22, 2008.

The southern Texas Hurricane Dolly is now at a category 2 on the Gulf Coast.

Meanwhile, Chicago is currently having a low humidity, 78 degree, beautiful day!

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Chicagoans haven't experienced daytime temperatures cooler than Tuesday's
77-degree high at O'Hare since July 4. These readings fall 7 or more degrees short of
84 degrees, a level considered normal this time of year, and come only two days ahead
of the 74th anniversary of the city's hottest official temperature on record: 105 degrees
on July 24, 1934.

The 2008 warm season has been noteworthy for its lack of extreme or extended heat.
While the city's 39 days of highs of 80 degrees or higher to date are close the
long-term (80 year) average of 43 at Midway Airport, the 2008 warm season has
produced only three days at or above 90 degrees at the official thermometers at O'Hare
and five days at Midway, well short of the 13 days which have occurred by July 23 on
average since 1928. Northeast winds continue off Lake Michigan on Wednesday
promising another day of very moderate summer temperatures.

DOLLY THE FIRST HURRICANE OF 2008 TO LAND ON U.S. TURF

Dolly, a minimal hurricane, crashes into the south Texas coast Wednesday. The 2008
hurricane season is really humming in the Atlantic Basin. Normally the fourth named
storm of the season occurs around Aug. 26 -- making Dolly more than a month early.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I am in charge of planning an annual summer party and it has rained the last few
summers on the weekend chosen. Historically, which weekends in July and August is it
least likely to rain?

Bob Haza, Oak Brook, Ill.

Dear Bob,

When it comes to avoiding a rainy weekend, it doesn't matter which dates in July and
August you select. The chance of rain is the same on any given day in those months: 31
or 32 percent. That's the result of a computer scan of 137 years of Chicago's daily
rainfall records. You can attribute your rainouts in the last few years to bad luck rather
than to poor planning. But consider this: Thunderstorms account for most of Chicago's
mid- and late-summer rainfall, and August thunderstorms tend to be of shorter
duration. That suggests an August outing is slightly preferable. The tradeoff is that
August storms, on average, produce more intense (but more brief) rain.

Thank you for checking in with Tom Skilling's ‘Before the Forecast’ for Tuesday, July 22, 2008.

As predicted last night, that cool, dry air is here to produce the coolest temperatures in the past 18 days. You can thank the Northeast winds blowing off of Lake Michigan for the reduced and comfortable summer temperature.

Average temperatures for this time of the year are usually at mid-80 degrees. Today, we will experience temperatures in the lower upper 60's to lower 70 degrees.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Kevin lange from about 60 miles northeast in Seneca took this photo of the thunderstorms as they rolled through Peoria and Bloomington around 9 p.m., Monday, July 21.

Thanks for the photos Kevin!

Photo courtesy of Kevin Lange

Keith and Rita Matthews and their daughter were on a Caribbean cruise last week when,
in Georgetown, Grand Cayman, a developing thunderstorm entered the picture.
Keith takes us from there:

"Suddenly there was a lot of lightning--huge bolts! My wife and daughter were up
on the top deck by the pool and quickly took cover as the storm rolled in. As they
looked toward the city they said they did a double-take. They couldn't believe what they
saw. It was a funnel cloud. Fortunately they had the camera and took several pictures of
it. I don't believe it ever touched down but it was incredible to see. This was just an
island storm, not associated with a hurricane. Again this was last Wednesday, July 16.
We have lived in the Chicago area all our lives and have never seen a funnel cloud or
tornado. We go to the Caribbean and, viola! A funnel cloud! Who'd of thought!"


Thanks for sharing this with us Keith and Rita! Terrific photos and quite a story!

Tom Skilling

Photos courtesy of Keith and Rita Matthews

Heat and humidity are taking a midsummer break in the Chicago area after a stormy,
muggy weekend that brought as much as 2.8 inches of rain to portions of Will County
since Friday. While the Chicago area escaped with just some light rain Monday morning,
other parts of the state were raked by damaging winds. Gusts estimated at 90-100
m.p.h. killed one and injured nine just east of the Quad Cities while winds reached 75
m.p.h. at Momence, 65 m.p.h. at Marseilles and 60 m.p.h. at Bourbonnais. City
precipitation totals approaching 9 inches since June 1 are making this the wettest open
to meteorological summer since the benchmark flood year of 1993, but drier, cooler
and less humid weather is headed for this area as a buckling jet stream delivers a
Canadian air flow.

STRENGTHENING DOLLY HEADS FOR SOUTH TEXAS

Tropical Storm Dolly, packing 50 m.p.h. winds, is expected to strengthen Monday as it
traverses the bathtub-warm waters of the western Gulf. Dolly could become a hurricane
before it makes an expected landfall near the south tip of Texas Wednesday afternoon.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Where does Illinois rank among the states in annual rainfall? Who's the
wettest and who's the driest?

Karen Samuelson

Dear Karen,
Average precipitation (rain plus the water equivalent of melted snow) across
the lower 48 states is about 30 inches per year. If none of it evaporated,
soaked in or drained off, a 30-inch layer of water would flood the country
after one year.
The nation's average annual precipitation is not distributed evenly, of
course. The land surface of the United States, which ranges from barren
deserts to lush rain forests, attests to that. And even within many states,
especially those with mountains, precipitation varies greatly.
On average, though, Louisiana, with 55 inches, is our wettest state; Nevada,
with a scant 9 inches annually, is the driest. Illinois, with 37 inches,
ranks 27th.

Thank you for checking in with Tom Skilling's "Before the Forecast."

Cool, dry air is coming to the Chicago area tomorrow, after a chance of scattered thunderstorms just west of the city.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Thanks to Chuck Hagen for this shot of a shelf cloud taken as thunderstorms raced through Iroquois County this morning.

Photo by Chuck Hagen

Despite several rounds of showers and thunderstorms that brought significant rainfall
totals to the metropolitan area, Chicagoans still had enough sunny and dry hours to
salvage some outdoor activities on a warm, muggy midsummer weekend.
The week ahead promises a respite from last week's hot and muggy conditions with
readings most days expected to top out with seasonable highs in the lower 80s coupled
with comfortable humidity levels.
After some lingering showers and thunderstorms move out of the area Monday, dry
conditions are expected to hold until Friday when showers may develop in a surge of
warmth and humidity ahead of an approaching cold front.

ATLANTIC BASIN QUITE ACTIVE
Even though Bertha has lost its tropical characteristics as it heads for Iceland after a
record 17-day trek through the Atlantic, it was still packing 70 m.p.h. winds Sunday
evening. (Bertha set a new record for the longest-lasting tropical storm in July.)
Elsewhere in the tropics, Tropical Storm Dolly appears headed for a rainy rendezvous
with far south Texas by the end of the week, while Tropical Storm Cristobal will lay a
swath of heavy rain as it skirts the Atlantic coast as it heads for Nova Scotia.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
In a recent column you said that the dog days of summer are here. I thought
those were in August when the dog star is seen in the sky?
Rose Hedman
Dear Rose,
The term "dog days" of summer refers to periods of hot and humid weather
that typically occur in many parts of the Northern Hemisphere during July
and August. The term's origin dates back to ancient times when the Egyptians
believed that the appearance of Sirius, the Dog Star located in the
constellation Canis Major (The Great Dog) in the early morning sky added its
heat to that of the sun to produce exceptionally hot weather. Astronomically
the Egyptians calculated the dog days from July 3-August 11. In more modern
times, the term has been applied to extended periods of late-summer hot
weather lasting up to a week or more, usually in August.

A frontal system squirming through a very warm air mass loaded with moisture sets the
stage for more thunderstorms Sunday, Sunday night and Monday. This morning the
southern edge of a strong complex of thunderstorms moving east into central Lake
Michigan will pass over northeastern Illinois. Scattered downpours and possible severe
weather may be experienced in the Chicago area, especially to the north near the
Wisconsin line. Some sailboats in the Mackinac race could get caught in the
thunderstorms over Lake Michigan and bucking easterly winds the remainder of the race
to the Straits of Mackinac. The sun should break out over the metro area later Sunday
morning. Then heating will push temperatures back to the 90-degree level, triggering a
possible redevelopment of thunderstorms.

ANOTHER SURGE OF STORMS TONIGHT AND EARLY MONDAY

One last low-pressure disturbance is expected to ripple through northern Illinois
Sunday night and early Monday, driving the frontal system south beyond the Ohio River.
Heavy downpours may occur. Later Monday, the southern portion of high pressure
centered over Canada will push into the southern Great Lakes and Midwest, bringing
milder, less humid air to Chicago.

Dear Tom,
I thought that if a storm develops into a hurricane its name is retired. I remember
another Hurricane Bertha that was threatening Ft. Lauderdale in 1996. What gives?

—Fred Zagone, Milwaukee

Dear Fred,
The list of Atlantic Basin tropical cyclone names is repeated every six years,
and Category 3 Hurricane Bertha, with top winds of 115 m.p.h., did indeed threaten
Florida before making a North Carolina landfall on July 13, 1996. Tropical Storm Bertha
made a Louisiana landfall back in 2002, and in 1990 Hurricane Bertha brushed the
Canadian Maritimes. Hurricane names are retired only if a storm is deemed historically
noteworthy, usually in terms of damage or loss of life. Previous storms named Bertha
did not merit retirement status and unless this season’s Bertha becomes memorable,
there will be another Bertha in 2014.

Acting on a moisture-laden atmosphere, heating by ample sunshine triggered widely
scattered thunderstorms across the Chicago area Friday afternoon, and the storms
continued into the evening hours.
While many areas went rain-free, other locations experienced very heavy downpours. A
weather observer in Arlington Heights recorded 3.26 inches of rain between 6:30 and 8:45
p.m., while in the late afternoon, an observer in Wilmington, just south of Joliet in Will
County, measured 1.90 inches in one hour. As a large heavy rain area developed and
persisted over northern Cook County, the National Weather Service issued a flash flood
warning at 8:45 p.m. for that area.
ADDITIONAL HEAVY RAINS POSSIBLE
With a frontal system acting as the stimulus, thunderstorms could trigger rainfalls in
excess of 2 inches at many locations in northeast Illinois Saturday through Monday.

--By Paul Dailey, WGN Weather Center Meteorologist

Dear readers: Yesterday's column contained an arithmetic error. Here is a
correction.

Dear Tom,
You indicated the water level in Lake Michigan has risen seven inches since
July 2007, and that rise added 2.73 trillion gallons of water. What happens
at the evaporation end? How much water evaporates from Lake Michigan?
Carl Gaines
Dear Carl,
Atmospheric processes operate on a scale that boggles the mind, and the
evaporation of water from Lake Michigan into the atmosphere is no exception.
Lake Michigan's 22,300 square miles of surface area loses 29.5 inches of
water annually via evaporation. That loss works out to a staggering 11.51
trillion gallons of water per year, or a daily average of 31.5 billion
gallons.
Here's the actual number: 31,500,000,000 gallons of water lost to the
atmosphere from Lake Michigan daily via evaporation.

Thunderstorms--some towering to heights of 32,000 feet according to
Doppler scans--erupted across Chicago's northwest suburbs before noon
Friday, and then proceeded eastward.

Our friend and regular weather blog photo contributor Anson Mount sent us
this photo of the downpours as they first arrived in Algonquin.

Photo courtesy of Anson Mount

These storms won't be the last in coming days. The atmosphere is primed
to erupt with thunderstorms at regular intervals heading into the weekend. Anson
reports 0.75" fell in 20 minutes--an early indication of how much rain the heavier
thunderstorms will be producing in coming days. Many thanks for the report and
photo, Anson!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Thunderstorm "debris" cloudiness -- remnants of dissipating thunderstorms that
flared to our west Thursday -- has spread across the area overnight. It's a development
that might bring an errant shower or two to parts of the area -- but is more likely to
reduce the amount of sun blazing down on the area Friday, possibly preventing a fourth
day of 90-degree temperatures over much of the area. Highs Thursday fell just short of
90 degrees at O'Hare (89 degrees) but surged to 91 degrees for the third consecutive
day at Midway. Other area highs included 93 degrees near U.S. Cellular Field on the
South Side and 92 degrees at New Lenox and at Griffith, Ind.

The storms which erupted to Chicago's west Thursday over Iowa and Nebraska may
hold clues to the weather ahead here. Drenching thunderstorm rains, which fell at the
rate of 1.90 inches in just 35 minutes near Table Rock, Neb., and 1.76 inches at the
National Weather Service Office at Hastings in just 25 minutes, caused widespread
street flooding.

TROPICAL FORECASTERS MONITORING T-STORMS DRENCHING SOUTHEAST

Conditions favor possible development of a disturbance off the Florida coast.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Thank you for checking in with Tom Skilling's "Before the Forecast."

After a high of 91 degrees today, Chicago will continue to experience a hot and muggy evening.
Big storms are brewing out in the West near Nebraska, but they won't hit near Illinois tonight.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

A gush of cooler air, generated by downpours out of powerful Wisconsin
thunderstorms, raced into the city on 35 m.p.h. gusts late Wednesday, offering
Chicagoans a burst of heat relief. The storms spent the day traveling southeast across
the Badger State, unleashing 70 m.p.h. winds gusts at Sheboygan and more than 4
inches of rain near La Crosse, before swiping extreme northeast Illinois. At one point,
clouds within the storm cluster towered to more than 52,000 feet. The outflow's arrival
sent Chicago temperatures tumbling from the mid-80s to the upper 60s. The plunge
followed a second day of 90s -- including 94 degrees at Alsip and 93 at Lincolnshire.
O'Hare and Midway Airports recorded the third 90-degree readings of 2008 topping out
at 90 and 91.

Combined with muggy, Gulf Coast-level 70-degree dewpoints, heat indexes peaked at
97 degrees on the South Side and 96 degrees at O'Hare -- the year's highest.

WORRISOME ATMOSPHERIC COMBO COULD IGNITE BIG RAINS THIS WEEKEND
Winds converging along a southward sagging cold front in an atmosphere saturated
with more than 2 inches of evaporated moisture could set the stage for clusters of
downpour-generating t-storms this weekend in parts of the Midwest.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
You frequently point out that heating from sun during the day leads to afternoon and
early evening thunderstorms, but why do we have so many storms late at night when
there is no heating?
Malcolm Vye
Dear Malcolm,
While thunderstorm activity does peak during the late afternoon when
atmospheric heat reaches its highest level, Chicago experiences a "secondary
thunderstorm maximum" between 2 and 5 a.m.

Retired National Weather Service research meteorologist Robert Johns tells us:

"The energy of wind that is lost in friction with the ground during the day, when
it is windy, remains in the atmosphere at night when surface air cools and ground-level
winds die away. With less energy lost to the ground, winds in the 1-4 thousand foot
level actually increase at night, and can more effectively transport heat and moisture to
generate thunderstorms."

This gorgeous sunset was taken Monday evening in New Buffalo, Michigan by Jenna
Durante of Woodridge, IL while taking a brief vacation with her family. Thank you for the
photo Jenna.

Bill Snyder, WGN Weather producer

Thank you for checking in with Tom Skilling's "Before the Forecast."

Temperatures reached a high of 91 degrees today, continuing with our summer weather of hot and humid heat.
Tonight, there is a chance of thunderstorms in the Northern regions of Illinois and Wisconsin.

Later tonight, temperatures are expected to cool down to the low 70's for a very comfortable Wednesday evening.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

The area's most persistent hot spell of the summer is under way and predicted to hold
into the weekend. The heat encompasses sections of 36 states and produced highs
approaching 100 degrees in Nebraska and Kansas. Here in Chicago, three -- and
possibly four -- additional 90-degree highs are on the way by Saturday. Temperatures
first reached 90 degrees at 1:50 p.m. Tuesday at Midway Airport and at 2.49 p.m. at
O'Hare -- only the second time this year the city's official thermometer has made it to
that benchmark reading. Other area highs included 93 degrees in New Lennox, Alsip
and Chicago's Lincoln Park and 92 degrees in Berwyn and Harwood Heights.

The heat accompanies the season's first build-up of ozone. The Illinois EPA's Chris
Price cautions those with respiratory ailments to avoid overexertion outdoors.

REPETITIVE T-STORMS THREATEN MAJOR RAINFALLS IN COMING DAYS IN THE WEST
AND NORTHERN MIDWEST

With the jet stream locked into its summer position paralleling the U.S.- Canadian
border, impulses are likely to ignite t-storms which travel over the same terrain
multiple times in coming days. It's a prime set-up for big totals in sections of the
Dakotas, Iowa, Nebraska, Minnesota and Wisconsin.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Why can you hear thunder so long after a lightning bolt? I have timed it to go on for
more than 40 seconds.

Dave Coleman, Naperville, Ill.

Dear Dave,

The phenomenal heating (about 50,000 degrees) brought to bear on a column of
air exposed to a lightning spark produces an explosive expansion and subsequent
contraction of the column—a process that sets up the shock waves we hear as thunder.

Rather than originating from a single point, these sound waves, propagating at about
1,100 feet per second, are generated along the entire length of a lightning stroke. That
length is often in excess of 10 miles. If a lightning bolt were oriented such that the
distance between its nearest and farthest points from you were 10 miles, the train of
sound waves thus generated would require 48 seconds to pass your ears. You would
hear thunder from that bolt for 48 seconds.

Thank you for checking in with Tom Skilling's "Before the Forecast."

Today, summer is in full swing with 90 degree tempuratures in the city and througout Chicagoland. Get outside and enjoy the day!

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Strings of 90-degree days -- like those predicted here for the remainder of the
workweek -- have occurred in 98 percent of the city's summers since 1928. But, the
first of them typically occurs on or about June 7. That makes the hot-weather period
predicted to dominate the area almost five weeks late. As many as four consecutive
90-degree highs are likely to occur here by the end of the week, something that has
occurred on 53 of the past 80 warm seasons -- or nearly two-thirds of the time.

The rain-cooled outflow of thunder- storms has reduced temperatures in each of this
year's warm spells to date. But warming aloft is to "cap" the atmosphere in coming
days, reducing prospects of rainfall. Though a steep vertical temperature drop this
afternoon may support a few thunderstorms in the area, most storm development in
coming days is to shift north into Minnesota, Wisconsin and Michigan near the jet
stream, which has migrated to its typical mid-summer location.

NORTHERN ILLINOIS CORN NEARING WEATHER SENSITIVE PERIOD

Illinois corn is nearing its pollinating stage. Regular rain and moderate temps become
important during this period.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
What is the rainiest month of the year in the Chicago area?
Frank Koral

Dear Frank,
The title for Chicago's rainiest month has been held by August since 1991, but it hasn't
always been the city's precipitation leader. Through much of Chicago's climate history,
August ranked only as the city's 4th or 5th wettest month, with June or July leading the
year. However, since around 1980 the city has become a magnet for heavy August
cloudbursts. The month's precipitation normals have skyrocketed from around 3.15
inches using data before 1970 to its current 4.62-inch total based on the latest
1971-2000 climatological normal period. Climate normals are recalculated every 10
years using the latest 30 years of data to reveal a "moving" climate picture of an area.
Dating back to 1871, seven of the city's 10 wettest Augusts have been logged since
1970, lead by August 1987 with 17.10 inches.

Thanks for checking in with Before the Forecast! The great videos and photos of the recent storms will continue, as Tom and his team work hard to share these great pictures with you.

Today, the beatiful summer weather continues with temperatures up in the the 90s. Learn the full details in today's edition of Before the Forecast.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Frequent contributor Tracey Surface sends us photos of these amazing lightning
strokes late Friday night---one looking west from her high rise in the Montrose Avenue
area toward Lincoln and Western Avenues and the second streaking earthward toward
Lake Michigan east of Montrose Harbor.

-Tom Skilling

After warming into the mid-80s away from Lake Michigan Monday, the remainder of the
work week may well see a series of days hitting 90 degrees or higher.
Readings of more than 90 degrees in the northern and central Plains are poised to cross
the Mississippi River, riding strong west to southwest winds Tuesday. With the jet
stream forecast to remain along the U.S.-Canadian border, Tuesday through Friday may
be the first time in nearly a year that Chicago will experience four consecutive days of
90 degrees or higher. The last time this occurred was July 31 through Aug. 3 of last
year.
So far this year, the official observation site at O'Hare International Airport has recorded
only a single day with a 90-degree high, 91 degrees on June 12. Last year by this time,
Chicago had experienced 10 90-degree days.
RAINS MAY HOLD OFF UNTIL WEEKEND
So far this month O'Hare has received 2.05 inches of rain, more than half the monthly
normal 3.51 inches. Unless thunderstorms drift south out of Wisconsin Wednesday
night, the next best chance of rain will be late Friday and Saturday in advance of a cold
front. Because this system is expected to be slow moving, downpours of an inch or
more may be possible.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
Why does wet skin feel so cold?
Robert Allen
Dear Robert,
It's due to the behavior of water molecules: They're in constant motion and
the warmer they are, the faster they're moving. We sense that motion as
heat.
In liquid form, water molecules are vibrating and tumbling around because
they're not bonded together the way they are in ice. In order for a
within-liquid water molecule to escape from the liquid into the air -- to
evaporate -- it must obtain greater speed, and this can happen through
random collisions with other molecules in the liquid (which thereby lose
some of their speed).
If, after a collision, a particular molecule already at the water's surface
has sufficient speed to break into the air, it takes its energy (its heat)
with it. That's heat lost from the liquid, which therefore cools, and that's
why water evaporating from our skin gets cooler.

A northwest flow aloft will bring a brief period of cooler, less humid air over northern
Illinois and Wisconsin through Monday. However, the primary jet stream then moves back
north, establishing a strong west-east flow along the U.S.- Canadian border. This setup
will allow warmer and more humid air to surge back into the Midwest on the nose of
strengthening southwest winds. For three straight days, Tuesday through Thursday,
Chicago's highs will most likely exceed 90 degrees, while readings at night will hold just
above 70 degrees. Should these conditions occur, daily heat indexes will peak in the
mid-to-upper 90s, with little respite at night.

Dear Tom,
July 5 was sunny, warm and calm at our house. Out of nowhere, the wind kicked up and
our neighbor's flag, launched it from its holder,and carried it slowly upward perhaps
100 feet. It traveled north for a minute and fluttered down 100 yards from where it took
off, then the calm winds returned. Any thoughts on this?

-Dave Kircher, Orland Park

Dear Dave,

Your neighbor's flag had a close encounter with a dust devil--but one
apparently containing no dust. Dust devils are vigorous, short-lived whirlwinds that
form on quiet days when warm air at the ground,heated by the sun, surges upward in a
tight corkscrew spiral. It's almost like hot air rising in a chimney. The whirls, usually
made visible by dust in their 20 to 40 m.p.h. winds, can grow to several yards across
and a few hundred feet in height before dying just as suddenly as they appeared.

Temperatures across Chicago's south and southwest suburbs surged above 90 degrees
Friday. Highs there included 92 degrees at New Lenox and Markham, and 91 degrees at
Alsip and Griffith, Ind.
But the rain-cooled outflow from a diminishing cluster of thunderstorms sent easterly
lake breezes across much of Cook and Lake Counties in Illinois and into southeast
Wisconsin -- again sparing that portion of the Chicago area a 90-degree temperature.
New waves of thunderstorms were predicted to sweep the area overnight into this
morning. They come on the heels of five separate thunderstorm clusters the past two
days -- the most dramatic of them responsible for Thursday evening's widely observed
and photographed "shelf clouds."
Saturday's storm threat is the product of an approaching cold front that spawned at
least eight twisters in Minnesota -- some from 58,000-foot-tall thunderstorms.
RECORD RAINS SWAMP TUCSON
Monsoon-type rains hit the Southwest on Friday, scuttling the extreme heat of recent
weeks there while dropping 1.66 inches of rain on Tucson, Ariz. -- that city's
11th-wettest single calendar day in July.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
During a recent thunderstorm with strong winds, cars on the Eisenhower
Expressway were stopping in the underpasses. Is this safe? It sure messed up
the traffic.
Richard Waller
Dear Richard,
Your question comes up frequently. The answer: It's a very dangerous thing
to do.
Contrary to popular belief, expressway underpasses do not offer safe shelter
from the high winds of severe thunderstorms. Because of channeling and
funneling, winds actually blow stronger when they sweep through expressway
underpasses and beneath bridges, thereby increasing the risk of injury from
airborne debris.
Misconceptions about the safety of underpasses probably originated with a
widely circulated video of motorists rushing to an underpass in order to
avoid a tornado that was crossing Interstate 35 near Wichita, Kan., on April
26, 1991.

You've sent in TONS of great videos and photos of the recent storms, and Tom and crew have been working hard to share these great pictures with you. Check them out in the entries below!

As far as weather today, the summer heat kicks in with temperatures reaching up in the 90s. Learn the full details in today's edition of Before the Forecast.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

We'd like to send out a special thank you to everyone who sent us photos from Thursday's storms -- it was an incredible batch of images that ranged from a never-before-seen "lightning behind a rainbow" snapshot to views of the approaching derecho and storm clouds from across the Chicago area.

Here's a quick shortcut to all the photos we've posted on the blog from Thursday's storm.

(Note: Due to the number of photos, it may take a minute or two for all the photos to fully load.) We hope you enjoy these photos as much as we do.
—WGN-TV Weather Center

Mike Frankowski has outdone himself again. He sends us this shot taken in Sycamore Thursday evening right after thunderstorms swept through the area. Here lightning out of a thunderstorm anvil arcs across a sky which included this rainbow. Nice job, Mike! This is the first time I've seen anything quite like this!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Mike Frankowski, Sycamore, Illinois

This funnel cloud spun up over Hickory Hills as Thursday evening's derecho roared into the area. Deb Kozik shares this photograph with us. She took it in her backyard around 8 p.m. Thursday. It's a terrific shot, Deb! Many thanks!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Deb Kozik, Hickory Hills

Sue Lencioni is a flight medic with Air Angels, Inc., and has sent us these airborne shots of Thursday evening's derecho. Sue was in the air returning from Peoria when she and her crew came up on the storm. Thanks a very different angle on Thursday evening's storm!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Sue Lencioni, flight medic with Air Angels, Inc.

No section of the Chicago area was immune from Thursday's storms which are shown
transforming day into night in Oak Lawn in these photos relayed to us be Chuck Hagen.
Thanks Chuck!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Chuck Hagen

Pam Moralde of WGN witnessed Thursday's ominous storm clouds near her home in Tinley Park, and was kind enough to share this picture with us for our blog. Thanks Pam for the wonderful image!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Pam Moralde, Tinley Park, Ill.

Thursday was a busy day for Dr. Walker Ashley, a member of Northern
Illinois University's meteorology faculty, who forwards these amazing
shots to us. He storm-chased twice during the day in the De Kalb and
Kane County areas west of Chicago. It was during one of his chases he
photographed Thursday evening's southeastbound squall line sweeping into
the area. Many thanks to Dr. Ashley for the amazing shots and our best
to all involved with NIU's highly regarded meteorology program!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Dr. Walker Ashley, Northern Illinois University, De Kalb

Many thanks to storm chaser Chad Cowan who has sent us these photos of Thursday evening's impressive storm. Great shots, Chad!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Chad Cowan, Chicago

Many thanks to Carolyn Szepanski of Whiting, Indiana, for sharing these shots of Thursday's storm.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Carolyn Szepanski, Whiting, Indiana

Our former intern and Northern Illinois University meteorology graduate Patrick Korellis shares this photo of Thursday evening's shelf cloud. Great shot -- and great hearing from you, Patrick!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Patrick Korellis

Barry Hass, who shares these photos with us, reports there was "lots of
turning and churning" going on as the shelf cloud associated with
Thursday evening's derecho moved into Frankfort. We like the
description, Barry -- well put!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Barry Hass, Frankfort, Illinois

Patti Mullen shares with us these views of Thursday evening's stormy skies over Frankfort. Thanks Patti!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Patti Mullen, Frankfort, Illinois

That's how Noreen Stewart of South Elgin described the scene Thursday evening around 7 p.m. in that west suburban community. "As it moved over our house, it looked like a spaceship passing over." It's a great description, Noreen! This shelf cloud, which spanned the entire Chicago area and beyond as it moved in, caught the eyes of nearly everyone who saw it across the Chicago area.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Noreen Stewart, South Elgin, Illinois

Trish Schager's photo of the storm sweeping into Joliet Thursday evening all but takes us there. Great shot Trish!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Trish Schager, Joliet, Illinois

Photo courtesy of Rich Ricar, Western Springs

Stephani Ross, who shares this shot with us, was driving west on Route 20 in Elgin with her grandmother and cousin when she snapped this shot of the storm moving in! It's great, Stephani! Thanks!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Stephani Ross, Elgin

Christopher Morsch sends us these dramatic shots from the Golf Club of Illinois in McHenry County Thursday evening. Thanks Christopher!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Christopher Morsch, McHenry County

Thanks to Julie Schroeder for e-mailing us these shots from Sycamore, Illinois!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Julie Schroeder, Sycamore, Illinois

Thanks to Tracey Surface for these revealing shots of Thursday evening's ominous skies.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Tracey Surface, Chicago

The Lilianstrom family of Streamwood was at the Chicagoland Speedway in Joliet as Thursday's squall line moved in around 7:30 p.m. Al Lilianstrom took this photograph and shares it with us. Many thanks Al -- great shots!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Al Lilianstrom of Streamwood

Photos courtesy of Rich Ricar, Western Springs

Video from north suburban Round Lake of the arrival of Thursday¹s storms.

Watch as the storm sweeps into Lake County's Round Lake courtesy of this video from Bob Fesus shot at one frame every four seconds. Great video Bob!
Many thanks!

A powerful squall line -- at one point racing southeast at 60 m.p.h. and generating 700
cloud to ground lightning strikes every 10 minutes -- arrived with eye-catching fury
late Thursday. Downpours accompanied by wind gusts as high as 75 m.p.h. swept
Janesville, Wis., then moved on to north suburban Wheeling (63 m.p.h.) and McHenry
County's Lake in the Hills (60 m.p.h.). Some trees were downed primarily across the
northwest suburbs. The evening squalls began 600 miles to the northwest at around 6
a.m. Thursday in North Dakota. The southeastbound and persistent line of storms,
referred to by meteorologists as a derecho, produced damage over four states --
lambasting the Twin Cities around lunchtime and downing trees in the Madison, Wis.,
area mid-afternoon. Hail up to 3 inches in diameter bombarded Winsted, Minn. The
storms came on the heels of a nearly stationary cluster of storms responsible for hours
of lightning and rain centered on Lee County west of Chicago, where as much as 4.75
inches of rain fell at Sublette and 3.50 inches at Amboy.

MERCURY HEADED FOR 93 DEGREES THEN NEW STORMS TO HIT

New, potentially powerful storms develop in the wake of Friday's 93-degree heat late
Friday night.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Because rain falls so far from the clouds, why doesn't it damage whatever it
hits? For example, you would think raindrops would break my car windshield.
Is it more a physics question as opposed to a weather question?

Tami Stevenson, Elgin, Ill.

Dear Tami,

It's a question of physics -- the physics of raindrop stability. As a large
raindrop falls faster and faster through the air, the friction of its
passage through the air causes it to flatten, then to bulge upward in the
middle rather like an inverted paper bag, and finally to shatter into
smaller drops that fall more slowly.

It turns out the maximum size that a raindrop can attain before shattering
is 0.2 of an inch in diameter. The top fall speed of the largest "shatter-proof"
raindrops occurs when frictional drag equals the weight of the drop, and
that's 21 m.p.h. Fortunately, raindrops 0.2 of an inch across falling at 21 m.p.h.
don't cause damage.

Storm hitting Chicago

Photo by Dennis Erickson

Storm moving into Oswego, Illinois

Photo by Eric Karl

Storm in Alsip

Photo by Mike Z.

Chicago's Northwest side

Photo by Thomas Nava

Storm blasting Woodstock, Illinois

Photo by Brett Hansen

Storm at Grayslake
Photo by Dean Haverkampf

Crystal Lake Blasted

Photo by Ryan Kinross

Elgin getting hit

Photo by Tyler Christiansen

Nick Bilski captured Thursday's squall line sweeping across the city from the lakefront. Thanks Nick!

Tom Skilling

Photo courtesy: Nick Bilski

Thanks to EVERYONE who took the time to send us spectacular shots of Thursday
evening’s derecho. The squall line swept into the area late in the day with
the eye catching shelf cloud so visible in all of the photos. Shelf clouds
form as rain-cooled air gushes out the leading edge of a thunderstorm or line or
storms, cooling humid air in advance to condensation.

Our friend David Lindgren, who with his wife Colleen and their family, farms in De
Kalb County, shares these shots of a tree split by lightning in Thursday afternoon’s
storms. David tells us:

“We had a tree struck by lightning out here today, it was a quiet strike, not the
usual loud crack that makes you jump from your seat. I did not know that we were hit
until I saw the tree. This strike also blew apart a bird house in another tree about 65
feet away with no visible damage to that tree. My wife Colleen said that I did not have
to celebrate my birthday with a lightning strike to a tree next to the house. “

Great shots David. Many thanks!!

Tom Skilling

Photo courtesy: David Lindgren

Storm at Algonquin, Illinois

Photo by Anson Mount

Storm in Malta, Illinois

Photo by Nick and Erin Flink

Storm hitting Elburn, Illinois

Photo by Steve Parsons

Gust front passing Waukegan, Illinois

Photo by Robbie Culver

A fast-moving line of thunderstorms accompanied by high winds and heavy rain known as a derecho is sweeping the Chicago area this evening. Our viewers have passed on dozens of dramatic storm pictures as the storms moved thorugh the area Thursday evening.

Steve Kahn WGN Weather Center

Approaching Hampshire, Illinois

Photo by Brittney Misialek former WGN Weather Intern

Storm over Cary, Illinois

Photo by Matt Hoelter

Storm approaching Huntely, Illinois

Photo by Max Sanches

Storm bearinbg down on McHenry, Illinois

Photo by Tom Esser

Thank you for checking in with Tom Skilling's 'Before the Forecast.'

Today there are some big storms clobbering areas far west of Chicago with heavy rain and thunder. In the city, you can expect lighter showers scattered throughout the Chicago area.

Later tonight, Tom expects more hot and humid weather.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

Air conditioners will be humming Friday as some of the year's hottest temperatures and
a fresh surge of muggy Gulf air bear down on the Chicago area. A thermometer high of
91 degrees would equal this year's highest reading to date while a 93-degree high
would qualify as the Chicago area's hottest since a 94-degree reading on July 9 last
summer. The elevated temperatures originate from a vast reservoir of hot air which has
broiled the West in record-breaking triple-digit heat for days. Among Wednesday's
records in California was the 113-degree high at Redding, 110 degrees at Ukiah, 108
degrees at Sacramento and 107 degrees at Stockton. The addition of moisture as the
heat reaches Chicago threatens to push heat index readings into the 95-100-degree
range. Hurricane Bertha strengthened far at sea in the Atlantic on Wednesday and
threatens to attain Category 3 winds Thursday.

62% OF CHICAGO'S HOTTEST DAYS TYPICALLY ARRIVE AFTER JULY 10

Despite the lack of heat thus far this summer, history suggests that 62 percent (15
days) of Chicago's 90-degree or warmer days occur beyond this date.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I know that a dew point of 70 degrees or higher is a benchmark for being
uncomfortable. What is Chicago's highest dew point on record?
Jim Birkett Chicago

Dear Jim,
Many people begin to feel uncomfortable when the dew point reaches the
middle or upper 60s, but almost everyone is affected when the 70 degree dew
point threshold is crossed. In Chicago, the dew point typically climbs to 70
or higher about 30 times a year, most often in July and August. However, on
rare occasions dew points in Chicago can reach 80, a sweltering level most
common in summer along the Gulf Coast. The city has recorded an official 80
degree or higher dew point only six times, all in the month of July. Chicago's
highest-ever dew point was a stifling 83 degrees on July 30, 1999, and the most
recent steamy encounters with an 80 dew point were on July 7 and July 23 in 2001.

Thank you for checking in with Tom Skilling's 'Before the Forecast.'

Unfortunately, we are unable to bring you the webcam update at this time due to
technical equipment difficulties. This will be resolved for the morning.

Tune in tomorrow for another edition of Before the Forecast, and as always continue
to watch WGN for more coverage: Morning, Noon & Nine.

The thunderstorms pictured here in photos relayed to us by Carolyn Szepanski of
Whiting, Indiana doused scattered sections of Chicago’s west and southern suburbs
then swept into northwest Indiana Tuesday evening. Carolyn’s photos capture the
ominous appearance of these storms as they swept into the area. The storms’
downpours were so intense they produced large rainfalls in a short period of time.

Thanks Carolyn for these terrific shots!

Tom Skilling

Photos courtesy of Carolyn Szepanski, Whiting, Indiana

Meteorological Summer 2008 has moved into its 6th week with an overall temperature
surplus (about 1.5 degrees) but with its surprising lack of truly hot days still intact. It's
single 90-degree high ranks it with only three other summers since 1928 with so few
90s this late in the season. The warm season to date has registered only 28 days in the
80s -- a 28 percent reduction from the 39 days recorded a year ago. Tuesday's
85-degree high temperature and steamy 70-degree Gulf Coast-level dew points ignited
several downpour-generating late afternoon thunderstorms. In Oak Brook, one
downpour from a towering thunderhead, scanned by area radars at 40,000 feet high,
unloaded 0.68 of an inch of rain in 50 minutes. Midway Airport was hit with 0.25 of an
inch in just 14 minutes.

Hurricane Bertha encountered wind shear -- shifting wind direction and speeds with
height -- which stole a bit of the storm's punch. Sustained winds dropped to 85 m.p.h.
-- further weakening is predicted

WILDFIRE-RAVAGED CALIFORNIA SIZZLES WITH 110-DEGREE INLAND HIGHS

Temperatures hit 111 degrees at Lancaster and Paso Robles -- and 110-degrees at
Palmdale in California -- all records.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
If hurricanes are named alphabetically why is the season's first named storm Bertha and
not an "A" name?
Ed and Barb Wargo

Dear Ed and Barb,
Bertha is actually the season's second storm and that is why its name starts with the
letter "B". The first storm of the season, Tropical Storm Arthur came and went so fast
that many people missed it. Arthur formed inland about 45 miles northwest of Belize
City, Belize on May 31, moved west across the southern Yucatan and quickly weakened
to a tropical depression by the evening of June 1 near the Guatemala-Mexico border.
During its short lifespan Arthur could only muster top winds of 40 m.p.h., but it did
produce extensive flooding in Belize from up to 15 inches of rain. Five people perished
there and damage was estimated at nearly 80 million dollars. As the 2008 Atlantic Basin
hurricane season progresses, the next names to be used will be Cristobal, Dolly,
Edouard and Fay.

We’re becoming increasingly convinced photographer David Mayhew isn’t capable of
taking a bad photograph. Take in these stunning views of Tuesday evening’s sunset as
photographed by David from the West Loop. THANKS for the beautiful shots, David!

Tom Skilling

Photos courtesy or David Mayhew, Chicago

Tom Skilling takes a look at the stormy forecast for today. Watch WGN news at 9 for the complete 7-day forecast.

Thunderstorms were in their dissipating stage as they reach the city Monday evening.
But as these photos from Tracey Surface show, lightning was still visibile from her
vantage point near Montrose Harbor---though she was surprised their wasn’t more
thunder from the lightning discharges. Great photos as always—thanks Tracey!

Tom Skilling

Photos courtesy of Tracey Surface, Chicago

Loch Lomond National Park is a natural wonder as you can see in these beautiful photos
from Mike and Karen Vogan of Glasgow, Scotland. He writes:

“The sunshine beamed briefly between heavy downpours, part of a dominant
unsettled and wet weather regime which has put a damper not only to the Midwestern
US but across the Atlantic in Scotland, potential teleconnection?.”

It could well be, Mark. Thanks Mark and Karen for continuing to open our eyes to the
wonder and beauty of the Scottish countryside and weather! Your pictures play to rave
revierws here!

Tom Skilling
WGN-TV Meteorologist

Photos courtesy of Mark and Karen Voga, Glasgow, Scotland

We're never disappointed by Mike Frankowski's always amazing photos--and the set
of late last evening's spectacular cloud to ground and intracloud lightning as
thunderstorms raced across the northwest suburbs are NO exceptions! Check these out
and enjoy and our sincere thanks to Mike for sharing another spectacular group of
photos! Though Mike hails from South Elgin, he photographed the storm depicted in
these photos near Belvidere, Illinois.

Photos courtesy of Mike Frankowski

Thunderstorms rumble across parts of the Chicago area Tuesday morning. As on other
occasions in recent days, the storms strike an ominous pose as they gather in Iowa and
western Illinois then scatter and only selectively distribute their wind and rain once
here. Nowhere has this been more evident -- and for farmers and gardeners, more
frustrating -- than in Chicago's southern suburbs. There rain has been in short supply
this month. Lawns have gone brown in recent days and there have even been reports
that the leaves of corn plants have been curling, indicating stress from lack of
moisture. The irony is this has transpired at the same time rivers have flooded in the
northwest suburbs.

Monday evening's thunderstorms towered to 60,000 feet while pounding sections of
Iowa and Wisconsin with 70 m.p.h. winds and heavy rains.

BERTHA ONE OF 13 'MAJOR' EARLY SEASON HURRICANES TO FORM SINCE 1851

Hurricane Berth's winds strengthened to 115 m.p.h. late Monday, making it a Category
3 storm. It becomes one of only 13 early season hurricanes to attain "major" (Category
3) status.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Having observed the weather in Chicago for many years, I have concluded that
thunderstorms heading for the city dissipate or weaken before getting here,
then strengthen or reform east of the city; or they always pass north or
south of the city. Why is this?
Doug Mann

Dear Doug,
It might sometimes seem that thunderstorms occur less frequently and with
less vigor in Chicago than at surrounding locations, but area weather
records do not support that contention.

Historical data from National Weather Service and from the
observations of cooperative weather observers show that, over time,
thunderstorm frequency and intensity are quite uniform across northern
Illinois, northwest Indiana and southern Wisconsin.
Locations that thunderstorms repeatedly spare for weeks, even months, always
catch up when the weather patterns change--and eventually they do change.

Tom Skilling gives an update on the storm watch for the area, and it looks like there could be more flooding on the way. Watch out for Hurricane Bertha!

Still, temperatures continue to be above normal and cloudy for the rest of the week.

Thanks to Dennis Erickson for sharing this shot from Chicago's fireworks extravaganza taken on a clear, cool evening with a crescent moon in the background.

Photo by Dennis Erickson

Steve Kahn WGN Weather Center Meteorologist

Bob Carnes of Simi Valley, California took this picture at the Santa Barbara Airport shortly before sunset on Thursday July 3. Smoke from the nearby Gap Fire is filtering the setting sun.

Photo by Bob Carnes

Steve Kahn WGN Weather Center Meteorologist

A slow-approaching cold front will allow extended warmth and humidity punctuated by
frequent showers and thunderstorms over the same areas recently hit by copious rains
and flooding. There will be a risk of severe storms, but renewed flooding could be the
greatest concern as heavy downpours from some of the stronger storms may leave
many locations across southern Wisconsin and northern Illinois with rainfall totals in
excess of 2 inches before rains end with an expected cold frontal passage Tuesday.
As the southern edge of a cooler, less humid Canadian high-pressure region pushes
into the Midwest, the band of heavy rains should drift into parts of Missouri, Oklahoma,
Arkansas and Tennessee Wednesday and Thursday. Humid southerly flow and more
thunderstorms return to the Chicago area later Friday and Saturday.

--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
Does a very snowy winter mean a very wet summer?
Meredith Graf, West Chicago
Dear Meredith,
It does not. Broadly speaking, Chicago experiences its wettest weather --
heavy snow in the winter and heavy rain in the summer -- when upper-level
winds repeatedly direct low pressure systems and their attendant
precipitation from the southern Plains northeast into the Midwest. Storm
systems moving on that general path tap moisture from the Gulf of Mexico and
tend to produce copious precipitation at Chicago.
However, such weather patterns usually do not persist for months and months
at a time, that is, from the winter through the spring and summer.
We examined rainfall in the summers following Chicago's 10 snowiest winters
and did not find a snowy winter-rainy summer link. A very rainy summer
followed only two of the city's 10 snowiest winters.

As cool Canadian high pressure recedes to the east, southerly winds return to Chicago,
bringing warmer and noticeably more humid air back into the area. An approximate
two-day period of mid-summer-like heat, humidity and thunderstorms is expected to
begin later tonight. As a cold front approaches from the west, strong storms with heavy
downpours become more likely later Monday into Tuesday. Monday-Tuesday rainfall
totals could easily exceed two inches at many metro area observation points. The
southern portion of cooler less humid Canadian high pressure should hold over the
Midwest Wednesday and Thursday, with a shift in the jet stream flow allowing an
increasing southerly flow and the return of warm humid air next weekend.

--By Paul Dailey, WGN Weather Center Meteorologist

TROPICAL STORM BERTHA COULD BECOME HURRICANE THIS WEEK

Dear Tom,
Why are the Weather Service radars in Romeoville and elsewhere "down for
maintenance" so often? It’s troubling, especially during inclement weather.

Ray Deremo, La Grange Park

Dear Ray,
It's a matter of routine maintenance and computer software upgrades,
according to meteorologist Mark Ratzer at the Romeoville office of the Chicago
National Weather Service. Please note, though, that the surveillance patterns of
individual radars overlap. When a radar is out of service, storms within its primary
scanning area continue to be monitored by adjacent radars. Ratzer says the
Romeoville radar was occasionally down for maintenance this spring so panels in the
radar dome could be replaced, and also for an upgrade to the computer software that
processes radar data. That upgrade is being installed at all radars across the country.

The summer's warmest days typically follow in the weeks just beyond July 4. But you'd
never know it from the weather of recent days. Void of the stifling humidities so typical of
summer, the dry air of recent nights has permitted temperatures to drop quickly to levels
more typical of a month earlier. Friday opened with a 52-degree official low at O'Hare --
just two degrees off the 1980 record low of 50. Friday night's temperature decline was
predicted to yield 40s in far west suburban locations a second consecutive night.

Warming takes hold the remainder of the holiday weekend. The same air mass
responsible for a 102-degree high in Billings, Mont., and Denver's 97-degree peak
reading Friday is expanding eastward. Southerly winds within it are to tap Gulf moisture
in the next two days. In absolute terms, the amount of moisture in the air on Friday
here will quadruple by Monday. Its moisture is expected to fuel some clusters of
thunderstorms.
LAKE MICHIGAN STILL RISING
The Army Corps of Engineers reports Lake Michigan's water level is now 7" above a year
ago. That means the lake now holds 2.73 trillion gallons more water than it did the
same time last year.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I just returned from Costa Rica, and the people there boasted about never
having been hit by a hurricane. Can any of our Gulf or Atlantic states make
this claim?
Paul Brown
Dear Paul,
Because hurricanes seldom occur within 10 degrees latitude of the equator,
it is true that low-latitude Costa Rica has never sustained a direct
hurricane strike. (The country was hit head-on by a tropical storm in
December 1887.) However, Costa Rica can experience deadly consequences when
hurricanes strike areas farther north in Central America. Portions of the
country were devastated from floods and mudslides when Hurricane Cesar made
a landfall in Nicaragua in 1996. Hurricanes Mitch (1998) and Stan (2005)
also produced flooding in Costa Rica. In this country, no states on the Gulf
or Atlantic coasts are immune from hurricanes, with all of them recording
multiple landfalls dating back to 1850.

"The sky got dark and it looked like rain was coming in--but it was dirt," explains P.
Cummings, who shares this photo he took two weeks ago of dust blowing through the
air while he was in Dallas, Texas. Included in his photo set are aerial shots of towering
cumulonimbus taken while flying over Oklahoma. Our thanks for P. Cummings for
sharing these photos with us.

Photos courtesy of P. Cummings

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

While hot weather aficionados long for a dose of 90-degree temperatures, it's hard to
complain about Friday's weather. The gusty northeast winds responsible for readings
more typical of May or September during evening fireworks displays Thursday have
departed. Light east winds linger Friday, but will travel a fraction of the distance over
chilly lake water before reaching the city. That's likely to limit shoreline highs to the
upper 60s and low 70s for the Taste of Chicago, an improvement from Thursday's low
60s there.

Thursday's 71-degree official high at O'Hare ranks as the city's chilliest July 3 in 45
years. Not since a 67-degree high in 1963 has it been cooler.

Storms that drenched Chicago's northern suburbs late Wednesday went on to produce
record early morning rains in Michigan. Grand Rapids was hit with 3.18 inches -- the
third wettest daily July tally on record.

IT'S THE DAY EACH YEAR WHEN EARTH IS FARTHEST FROM THE SUN
July is Chicago's warmest month. But it's also the month Earth is farthest from the sun.
At 3 a.m. Friday, Earth was as far from the sun as at any point in the year -- what
astronomers call aphelion.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I remember that severe thunderstorms struck the Taste of Chicago in the early 1990s.
Was that a derecho?
Jim Smetana Arlington Heights

Dear Jim,
A derecho, a long-lived windstorm associated with a band of rapidly-moving
thunderstorms, did indeed sweep the Chicago area on July 2, 1992. The storm which
formed in the Plains the previous evening reached Chicago by mid afternoon, blasted
the area with wind gusts as high as 86 m.p.h. The storm killed one and injured several
dozen, capsized many sailboats on Lake Michigan, knocked down walls, unroofed
homes and devastated trees and power lines leaving more than 200,000 without power.
At the Taste at least six food booths and stages were overturned and the event shut
down for the day. The storm, accompanied by hail and torrential rain, also stopped
racing at Arlington Park and halted the Western Open golf tournament at Cog Hill in
Lemont.

Its almost too good to be true, but Tom Skilling has good weather forecasted for the upcoming week. The storms from last night are gone, revealing beautiful weather for everyone to enjoy the 4th of July holiday fireworks show tonight!

Midwesterners haven’t been the only ones dodging thunderstorms. Our friend Mark Vogan from Glasgow, Scotland tells us folks in his part of the UK have had their share of thunderstorms too in recent days. Here, Mark photographs the rainbows after the thundery weather. He writes:

“Captured these images this evening as a beautiful raindow shawn in the foreground of as today's 2nd pulse of thunderstorms darkened our evening sky. Steady and persistent rain follows the initial downpour as lightning lit the skies with embedded
rattles of thunder.”

Thanks for the great shots, Mark!

Photos courtesy of Mark Vogan, Glasgow, Scotland

Paul Havlik and his wife Karen cruised the waters of southern Alaska early last month
(June) and share these photos of the region with us. The sunset shot included here was
taken off the coastal islands near Ketchikan in the state’s Inside Passage. Paul and
Karen then proceeded north to Prince William Sound where they sailed College Fiord.
There, amid the mist and fog which can dominate the area given the abundance of
atmospheric moisture and the presence of mountains to lift and cool it, layered clouds
caught their eyes. These cloud formations can be driven or altered at times by the
cooling effect of glaciers. The chill which emanates from the huge masses of glacial ice
which can and does influence cloud formation there in many instances.

In commenting on his trip to Alaska, Paul tells us, “I have to admit that I was
enthralled with the landscape, views and wildlife.” That’s so well put!

It’s a truly amazing place and we thank Paul and Karen Havlik for being so good
about sharing their beautiful photos with us!

Tom Skilling

Photos courtesy of Paul and Karen Havlik, Mundelein, Illinois

Emily of Crystal Lake shares these images of downed trees and fence damage produced by
Wednesday afternoon and evening’s thunderstorms there. Many thanks for sharing these
with us, Emily!

Tom Skilling

Tom Skilling predicts severe weather for tonight. There have already been reports of trees falling, standing water, and flooding. Be careful out there tonight!

Chicago's north and northwest suburbs suffered a direct hit by powerful thunderstorms
late Wednesday, with flooding and wind-whipped downpours even as lightning arched
earthward up to 1,300 times in just 10 minutes. Tree limbs snapped from Crystal Lake
in McHenry County into sections of southern Lake County while motorists scrambled
for the shoulders of area roads as visibilities diminished in the blinding deluges. Gusts
hit 60 m.p.h. in far northwest suburban Lake in the Hills and 50 m.p.h. at Long Grove
while hails measuring 0.5 to 1 inch in diameter peppered Arlington Heights and
Algonquin. In Barrington, 2.10 inches of rain came down in just 30 minutes sending
temperatures diving 20 degrees.
After radar scans measured cloud tops which reached to 55,000 feet. A second wave of
storms, erupted late Wednesday evening from towering 49,000-foot clouds.

CITY OFFICIALS DECLARED A SWIMMING BAN AS LAKE LEVELS GYRATED

Wednesday's fast moving thunderstorms produced at least two seiches Wednesday
afternoon and evening. Seiches occur when thunderstorms set up gyrating lake levels.
Water levels shifted as much as 2 feet in Wednesday's seiches.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I remember a cold 4th of July in Chicago back in the 1960s. We were at a picnic and
everyone was huddled in blankets. What year was that?
Vanessa Sandler

Dear Vanessa,
The date was July 4, 1967 and the high in Chicago was an unseasonably chilly 64
degrees, just two degrees from the holiday's 62 degree record lowest maximum
established in 1920. The day was overcast with a brisk north wind adding to the chill.
Normally packed beaches and pools were all but deserted and many parties had to be
moved indoors. The next day was just as chilly with a high of 65, a reading that did
establish a record daytime chill for July 5. The city has not experienced a colder 4th of
July since then, though it was almost as cool in 1997 when the mercury topped out at
66. In contrast, the city's hottest July 4th took place in 1911 when the temperature
soared to 102 degrees.

Jeremy and Sarah share these storm damage photos taken in the Crystal Lake area
(northwest of Chicago in McHenry County) around 6 pm Wednesday evening. Some trees
and tree limbs snapped in the high winds. Many thanks for the revealing shots, Jeremy
and Sarah!

Tom Skilling

Photos courtesy of Jeremy and Sarah of Lake in the Hills

Photos courtesy of Tracey Surface, Chicago

Jay Kleeman sends us these photos of the northwest sububan storms at their height
this afternoon. Torrential downpours riding wind gusts as high as 50 to 60 mph
accompanied local 2.10” totals near Barrington in just 30 minutes Wednesday
afternoon while nearby Algonquin recorded 1.80”. Rainfall of 1.29” in 20 minutes was
reported 6 miles northeast of Buffalo Grove. Water 6” deep covered sections of Rt. 83
in Deerfield while as much as 5” was across a number of Highland Park roads for a
time. Fire department personnel in some northwest suburban communities arrived
with chain saws to tackle downed trees and tree limbs in some areas.

A swimming ban has been declared on Chicago’s beaches Wednesday evening
because of the feat of seiche conditions—rapid fluctuations in lake levels brought on
as winds surging out the front of fast moving, eastbound t-storms push domes of
water against the Michigan shoreline, producing reflected waves which return to the
Chicago and Illinois/Wisconsin shoreline of Lake Michigan leading to lake level
gyrations predicted this evening to generate lake level fluctuations of as much as 2
feet. Lightning in with the storms was prolific. As many as 1,300 cloud to ground
strokes were reported in a ten minute period as the powerful thunderstorms swept
through. More storms threaten sections of the Chicago metro area Wednesday
night---settlling slowly south with time. Complete weather coverage on WGN-TV
News and on our weather program tonigtht at 9 pm.

Photose courtesy of Jay Kleeman

Shortly after 5 p.m. a severe thunderstorm downed trees in Barrington. Anson Mount sent
in these pictures taken at 5:07 p.m. at Spring Creek near Rogers Bend Road.

Photos courtesy of Anson Mount

Sherry Forsee tells us the towering clouds pictured here, responsible for a storm
which swept into Roodhouse, Illinois—50 miles north of St. Louis---last Friday (June
27) were so tall, she couldn’t get the entire cloud in the picture! These are some
amazing shots---THANKS Sherry!

Tom Skilling

Photos courtesy of Sherry Forsee, Roodhouse, Illinois

A potent weather situation threatens to come together Wednesday afternoon and
evening -- one which threatens downpours and lightning-generating thunderstorms
accompanied at some locations by potentially powerful wind gusts. NOAA's Storm
Prediction Center has Chicago and surrounding areas of the Midwest outlooked for
possible severe weather. A cold front crashing southward on powerful northwest
jet-stream winds sweeps into humid, near-90-degree air -- an environment in which
atmospheric levels soar. It's this energy which powers t-storm winds and with nearly 2
inches of water evaporated in the atmosphere, the specter of local rainfalls of 1-3
inches isn't out the question in the hardest hit sections. It confirms a climatological
trend that has been observed in many Julys. Measurable rains become less frequent this
time of year -- occurring an average of 9 times per month. But the rains that fall can
be much heavier -- producing quick 1-2 inch tallies.

71% OF CHICAGO 90+-DEGREE DAYS OCCUR BEYOND THIS DATE

While hot weather's been in scarce supply this year, the area has typically recorded 7 of
the 24 days of 90-degree temps by July 2. That means summer is only getting going
with 71 percent of the areas's 90s to come.

--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Why is the study of weather termed meteorology? You don't study meteors, so why not
call it weatherology?
Stew Cherlin Park Ridge

Dear Stew,
The term meteorology dates back to early Greece (340 B.C.) when Aristotle wrote his
treatise "Meteorologica", a classic work that not only covered that era's knowledge of
weather and climate but also subjects relating to geology, astronomy and
oceanography. In Aristotle's time anything that was suspended or fell from the sky was
called a "meteor" including rain, snow, hail, and rainbows and meteoroids. Because
most of Aristotle's work dealt with weather, the term meteorology became linked with
weather and atmospheric studies and meteoroids become part of astronomy. Thus, in
the context of meteorology's contemporary definition, a meteorologist is a scientist
that studies weather and the Earth's atmosphere, not meteors.

It's July 1, and one-third of our meteorological summer is already over. Find out what Tom has to say about this summer's weather and what we can expect in the next few days.

My colleague and WGN-TV Director Mike Lasky shares these photos of lightning
discharges--even a rainbow--associated with towering cumulonimbus clouds last
week in Denver, Colorado. Spectacular shots-----THANKS Mike!!

Tom Skilling

Photos taken in Denver, Colorado last week courtesy of Mike Lasky