June 2008 Archives

July, historically the city's warmest month, has arrived and as if on cue, temperatures
are warming. After surging into the mid-80s Tuesday, temperature readings
Wednesday, propelled by southwest winds and the warmth-inducing subsidence of air
which takes place beneath the "nose" of a powerful jet stream, appear poised to
generate Chicago's second 90-degree temperature of the year. More ominously, the
ingredients for severe thunderstorms come together over the area making Wednesday
afternoon and evening a period which will have to be monitored.

The books closed on one of Chicago's warmer and wetter Junes overnight. The month's
70.8-degree average temperature was 2.4-degrees above the 137-year average here --
warm enough to rank among the area's warmest 28 percent of Junes. June's rain tally
of 4.18 inches ranked 48th of the 137 Junes for which there are records here.

UPPER WINDS BRING SMOKE FROM CANADA WILDFIRES TO MIDWEST

Smoke from wildfires burning in Manitoba and Saskatchewan is riding northwest upper
steering winds over sections of the Midwest. It may lend a yellow or orange cast to the
sky over parts of the region Wednesday.

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

Dear Tom,
You mentioned on the 9 p.m. newscast on WGN (on June 26) that telephone use
during a thunderstorm is dangerous. Does that include cell phones?
Carole Dussaussoy

Dear Carole,
It does not. Lightning's electric charge is conducted through the air and ground along
paths of least electrical resistance. If lightning strikes near a building (a tree next to a
house, for example), its electric charge can be conducted into the structure through
telephone and electric lines (even if they are buried) and underground water and gas
pipes. Using a corded telephone while a thunderstorm is in progress is discouraged
because the phone is physically connected by wires to the outside. A cell phone,
however, has no such physical connection and the electric current from a nearby
lightning strike cannot reach it. It is perfectly safe to use a cell phone during a
thunderstorm.

Tom Skilling triumphs over his web cam and returns in tonight's Before the Forecast.

They don't get much more spectacular than this. Check out these awesome shots of
towering cumulonimbus clouds photographed by John Vale. John lives in Wheeling but
was in Marshalltown, Iowa--northeast of Des Moines. This photo set shows the storm
"anviling out"---a process in which the top of the clouds begins fanning out
horizontally once the storm's updrafts break through the "tropopause"--the boundary
between the troposphere and the stratosphere. Steady or rising temperatures in the
stratosphere make the updrafts heavier than their surroundings and encouraging this
rising air to begins surging horizontally rather than vertically, lending the cloud top an
"anviled" appearance in time. Thanks for great shots John!

Tom Skilling

Photos courtesy of John Vale of Wheeling, Illinois

These are photos taken this past weekend of what was once Lake Delton, Wisconsin.
Until thee weeks ago, the lake spread across 267 acres and held an estimated 600
million gallons of water. During a “normal” late June weekend, Lake Delton would have
been home to frolicking swimmers and folks fishing, boating and taking in the quiet
splendor of one of Wisconsin’s incredibly beautiful locations. Instead, it sits in this
state---emptied in a furious nearly two hour, house-destroying torrent following the
rupture of one of the lake’s rain shores, weakend by this springs record rains which
came on the heel of a winter of record breaking snows.

The water rushed into the Wisconsin River—only 40 feet below. The photos here were
taken by Andrew Bauman, who’s wife Kim works in our Creative Service department here
at WGN and relayed them to us. What is seen here can only be described as surreal, even
eerie—revealing the lake’s muddy bottom---acre after acre of it-----once hidden by
lake waters. Kim tells us one of the shots shows George Mesi and his daughter Hannah
taking in the unbelievable scene before them. It’s worth noting that while Lake Delton is
closed, the Wisconsin Dells are open for business and that’s always plenty to do there.
Our thanks to Kim and Andrew for sharing these photos with us!

Tom Skilling

Photos courtesy of Andrew Bauman

For the second straight afternoon showers fell in the Chicago area, but unlike
Saturday's blasts of hail and damaging winds, Sunday's storms did little more than turn
a pleasant summer day into a chilly evening. Temperatures dropped 10 degrees to the
mid-60s with the onset of the showers, and by evening readings had fallen into the
lower 60s under leaden showery skies.
Sunshine should return Monday and Tuesday as temperatures climb back toward
seasonable normals. A burst of warmth should send the mercury into the upper 80s by
Wednesday, but another round of thunderstorms along a cold front should bring in
cooler weather for the 4th of July.
SEVERE WEATHER BLASTS EASTERN U.S.
High winds and hail raked the East Sunday with nearly 150 reports of severe weather
through mid-evening. Two-inch-diameter hail battered Jacksonville in southeast South
Carolina, while high winds damaged trees and power lines from New England to
Alabama. Severe thunderstorms blew over a row of tents at a Huntsville, Ala., air show,
killing one and injuring a dozen other people.
This same storm system was responsible Friday night for winds estimated as high as
115 m.p.h. per hour just west of Omaha.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
You recently corrected erroneous data that showed the record high and low
for June 5 occurring in the same year. Has that ever happened here?
John Dawson, Oak Park
Dear John,
For a city to establish a record high and record low on the same date is an
extremely rare event, one that has never occurred in Chicago. In most cases
extraordinary meteorological circumstances are required to accomplish this
feat. A dry atmosphere is almost always a prerequisite along with unlimited
sunshine, and clear skies and light winds at night. Such conditions were
present in August 2002 when a rash of same-day record highs and lows were
set in the western United States. Unbelievably, Park City, Utah, broke or
tied its record high/low three times in one week (Aug. 11, 13 and 15) and
Alamosa, Colo., did it on consecutive days (Aug. 25 and 26). A single
occurrence was also recorded on Aug. 25 at Safford, Ariz., northeast of
Tucson.

A delightfully sunny and warm Saturday afternoon turned violent as fast-moving severe
thunderstorms swept across the metropolitan area between 2 p.m. and 6 p.m. The storms,
packing high winds and hail, left a litter of limbs, branches and power lines throughout
the region. Wind gusts reached 74 m.p.h. at hard-hit DeKalb and 65 m.p.h. in Chicago’s
Rogers Park. Injuries were reported when the storms hit an Evanston art fair, knocking
down several tents while pelting the area with 1-inch hail. Lake Michigan boaters were
also affected by winds in excess of 60 m.p.h. when the storms reached the lakefront.
More showers are expected Sunday but aren’t expected to be severe.

TROPICAL CYCLONE UPDATE: EASTERN PACIFIC HEATING UP; ATLANTIC QUIET

Two tropical storms, Boris and Cristina, have developed in the Eastern Pacific, southwest
of Baja California. The storms are moving west and currently pose no threat to land. In
contrast, the Atlantic Basin remains free from tropical cyclones.

--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
I hear meteorologists use the term "clear" skies and "fair" skies. What is the difference
between the two?
—Larry Jahn, Macomb

Dear Larry,
The term "clear" skies means exactly that: a near or total absence of clouds. It is a phrase
that most meteorologists like to reserve for nighttime forecasts, preferring to use an
unqualified "sunny" on a cloudless day without the need to modify the sunshine forecast
with the usual qualifiers of "mostly" or "partly." "Fair," on the other hand, isused to
describe pleasant weather conditions. Its use implies no precipitation, limited low-cloud
sky cover, good visibilities and light winds. Many forecasters rely on a forecast of "fair"
for the hours of darkness when thin, high-level cirrus clouds are present; the stars and
planets are still visible, but the presence of these high clouds precludes the use of "clear."

Severe thunderstorm swept the Chicago area Saturday afternoon bringnig strong winds and hail to many areas. Our thanks to Thomas Nava for these great shots of the thunderstorms as they approached Chicago's northwest side.

Photos by Thomas Nava

Steve Kahn WGN Weather Center Meteorologist

Though a few showers and thunderstorms dampened parts of the Chicago area Friday,
severe weather and heavy rains plagued areas to the west, north and south of the city.
Nearly an inch and a half of rain inundated Burlington in southeast Wisconsin Friday
afternoon, most of it falling in just 25 minutes. Baseball-size hail pummeled Earlham,
Iowa, southwest of Des Moines, and in downstate Illinois, winds gusted to 80 m.p.h. at
Xenia, east of Salem.
It has been a rough week of severe weather across the nation: There have been more than
2,000 U.S. severe weather reports in 44 states since last Saturday.
All of the storms have a played a major role in Chicago's lack of hot weather so far this
summer. Only eight summers since 1928 have had fewer 90s at Midway Airport by this
date.
GREAT LAKES LEVELS ON THE RISE
Thanks to recent rainy weather across the Midwest, water levels in all of the Great Lakes
are higher than a year ago. Lake Michigan is up 6 inches in the last month.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
When we left Phoenix is was 105 degrees. Can it get that hot here?
Elise White Pearce
Dear Elise,
Triple-digit heat is common in Phoenix, occurring more than 100 days
annually, including 17 days when the mercury reaches at least 110. While
Chicago does experience 100-degree weather, it does so only on limited
occasions. Officially, the city's all-time hottest day was just 105 degrees
on July 24, 1934, but unofficially the city has recorded readings of 105
degrees or higher nine times at Midway Airport, most of them during the
torrid "Dust Bowl" summers of the 1930s. During the summer of 1934 the
thermometer reached at least 105 degrees five times, topped by a high of 109
degrees on July 23. The city's most recent encounter with extreme heat was
back on July 13, 1995, when Midway climbed to 106 degrees during a deadly
three-day episode of heat and humidity that claimed more than 750 lives.

Source: U.S. Army Corps of Engineers

Technical difficulties have prevented us from airing both Thursday night's and Friday night's Before the Forecast segment. We hope to be back online with a new Before the Forecast segment on Monday June 30.

Tom Skilling WGN Weather Center Chief Meteorologist

The heaviest thunderstorms have bypassed Chicago in recent days -- a trend which is
to end Friday. Cumulonimbus clouds -- the tall, cottony clouds from which
thunderstorms emanate -- towered over the city's skyline late Thursday. Radar scans
indicated several reached 42,000 feet in height and produced isolated downpours
responsible for 0.60 of an inch in Wilmette, 0.25 of an inch in Northfield and 0.21 of an
inch in Northbrook. But those storms paled in comparison to powerful clusters that
drenched sections of Iowa with as much as 5 inches of rain and produced deadly wind
gusts clocked at 68 m.p.h. in Indianapolis. Early reports indicated the winds may have
collapsed a building under construction resulting in three deaths.

Blistering heat in the Plains -- including a 103-degree high at Dodge City, Kansas --
spawned the storms that led to more than 300 reports of severe weather Thursday. A jet
stream settling south toward Chicago threatens to strengthen t-storms here later on
Friday and Friday night.

LAKEFRONT FLIRTED WITH 90 DEGREES THURSDAY

An 89-degree high was recorded at Northerly Island on Chicago's lakefront, where
nearby water temperatures reached a season high of 68 degrees.

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

Dear Tom,
"We will be vacationing in the Rocky Mountains in Colorado in early July and
camping out for several days, at an elevation of about 7,500 feet. What
effect does elevation have on sunburn times?
The Jansen Family, Chicago
Dear Jansen Family,
The atmosphere offers partial protection from ultraviolet (UV) light, the
component of sunlight that causes sunburn and other damage to our skin. It
stands to reason, therefore, that there is progressively less protection at
higher elevations.
Dermatologist Dr. Bryan Schultz (who prepares the sunburn times that appear
on this weather page) says, "UV intensity increases in an exponential
fashion as altitude increases, from 4-10 percent per 1,000 feet. With
Chicago at 620 feet, an extra 6,900 feet will increase UV over 50 percent.
Chicago's sunburn time at 1 p.m. on a clear July 5th would be close to 16
minutes, but under 10 minutes at 7,500 feet in Colorado."

Complexes (groups) of thunderstorms have erupted with stunning regularity in the
Plains and Midwest, rotating around blistering heat which sent readings from Texas
north to Kansas into triple digits. These so-called “MCS’s” (Mesoscale Convective
Systems) are among nature’s most prolific rain and lightning producers and often
nocturnal (nighttime) in nature.

These beautiful shots of Scotland in the UK come to us from our friend Mark Vogan who
photographed these astride a canal outside Kirkintilloch. Summer is in full bloom in that
beautiful part of our world as you can see here. And the days are long. Scotland on the
other side of the Atlantic is a far north as Hudson Bay on the North American continent.
Mark tells us:

“We have daylight's first glimmers from as early as 3.15am to as late as 11.15pm (20
hours +). On clear night's we can have a glimmer of daylight on our northern horizon all
night, making for failure of complete darkness on some of our clearest midsummer
nights.”

Many thanks to Mark and his wife Karen for sharing these magnificent glimpses of
Scotland with us!

-Tom Skilling

Photos courtesy of Mark Vogan, Glasgow, Scotland

Some other shots Mark shared with us recently from Scotland in a cloudier weather
regime at the summit of Campsie Hills away from the city of Glasgow:

Thunderstorms lambasted northern Missouri and sections of central Illinois producing
stunning 6 to 8" rains in a region still reeling from flooding and wet ground. The
stunning rains were part of a complex of thunderstorms -- what meteorologists refer
to as an "MCS or Mesoscale Convective Complex. These are the bright clusters of
thunderstorms visible on satellite animations which seem to spring from thin air --
then linger for hours. A powerful and persistent low level wind extending from the Gulf
of Mexico north to the Plains fueled early Wednesday's storms, supplying them a rich,
nearly unlimited supply of moisture of hot humid air which has dominated the Plains.
Thunderstorms with MCS's are prolific lightning producers and can linger for 6 to 8 or
more hours. Linneus, Missouri was hardest hit with 8.61" while nearby Ethel reported
7.88" . New storms, towering to heights of 55,000 ft., flared late Wednesday in Iowa
and threatened a new round of heavy. Golf ball size hail and 60 m.p.h. accompanied the
storms in Nevada, Iowa -- just east of Ames.

KANSAS BROILS NEAR 100∞ WEDNESDAY

Temperatures reached the century mark in Kansas. The hot dome of air will continue
supporting t-storm clusters along its northern periphery.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Are there other countries that experience as many tornadoes as the United States
does?
Tom Skill, Peotone, Ill.
Dear Tom,
Nowhere in the world do more tornadoes occur than in the United States. The
latitude, geography and climate of this country provide a perfect breeding
ground for tornadoes unsurpassed anywhere in the world. As a result the U.S.
lays claim to nearly three-quarters of the world's twisters, the vast
majority occurring east of the Rockies.

However, tornadoes can and do occur in other parts of the world with the exception of
the polar regions. Areas with significant tornadic activity include Europe, Australia,
Canada, Russia, Argentina, China and Japan. In Bangladesh, at least a dozen twisters
have killed more people than the U.S.'s deadliest storm, the 1925 Tri-State tornado with
695 fatalities.

Northern Missouri and central Illinois were lambasted again overnight by torrential rainfall
accompanied by spectacular lightning—the by-product of a cluster of powerful
thunderstorms referred to by meteorologists as a Mesoscale Convective Complex—or
“MCS”. Most often nocturnal (nighttime) in nature, MCS’s have a history of generating
incredible lightning displays which can go on for hours. Paul Hadfield stepped out of
work around midnight last night in central Illinois and took these remarkable lightning
photographs which he is sharing with us. Thanks Paul!

Tom Skilling



Photos courtesy of Paul Hadfield, Central Illinois

Few meteorological phenomena are capable of crop damage or devastation more than
hail. As illustrated in these telling images sent to us by Michael A. Moore, a hailstorm
can literally decimate a corn field as happened this past weekend in northwest Indiana’s
Medaryville—located roughly halfway between Rensselaer and Winamac. Michael tells us
these shots were taken this past Saturday and Sunday, June 21 & 22. Thunderstorms in
coming days threaten to be hail producers over portions of the metro area, including
area farms, a development which will have to be monitored closely. My thanks to
Michael for sharing his pictures with us. They are very telling.

Tom Skilling

Photos courtesy of Michael A. Moore of the Medaryville, Indiana area

Surging temperatures and humidities in coming days will lend an ominously explosive
quality to the atmosphere. Among the risks this poses to the Midwest is the potential for
thundery interludes in which downpours generate large rainfalls—bad news for a region
still reeling from near record flooding. Just where the heaviest storms erupt is always a
dicey call for forecasters. While rising temperatures and some of the summer season’s
most humid air provide the building blocks for thunderstorms, the rain cooled air that
gushes from such storms plays a big role in determining the areas exposed to the most
prolonged bouts of rain. With the atmospheric water content headed for nearly 2 inches,
there will be plenty of moisture for any storms to tap.

The delightful low humidities of recent days are a thing of the past for the remainder of
the work week. Dew points, a measure of atmospheric moisture, are headed for the 70s
later Wednesday for only the fifth time this year. A shift in wind direction from the ground
to higher altitudes is just the sort of environment in which thunderstorms rotate and
generate gusty winds. Hail and lightning are obvious risks in this situation.

Dear Tom,
What does a 30 percent chance of rain mean?
-Magee Amethyst
Dear Magee,
The percent chance (or probability) of rain is the forecaster's way of
expressing how certain he is that it will rain. Ideally, a forecaster would
prefer to issue a zero-percent forecast (it absolutely will not rain) or a
100-percent forecast (it absolutely will rain), but the present "state of
the art" does not give forecasters that ability.
The proper interpretation of a 30 percent chance of rain (assuming the
forecasts verify perfectly) is that you will have rain on your head three
out of ten times that you hear such a forecast.
Please note that the percent chance of rain does not address the duration of
rainfall (it might rain all day or only a few minutes) or the amount of rain
that comes down (unless the forecaster uses a qualifying term such as
"heavy" or "light").

Our thanks to Dennis Erikson for sharing this photo of Sunday’s rainbow with us!

-Tom Skilling


Photo courtesy of Dennis Erickson

Tom Skilling predicts that its going to warm up, its going to get humid, and that we've got more rain on the way.

Our intrepid astronomer Dan Joyce has forwarded this spectacular shot of Jupiter,
photographed by his colleague Don Parker. As Dan e-mailed to us:

"Jupiter is dominating the southern sky this summer. Anyone can see it in a clear
sky to the southeast before midnight and in the south thereafter for the rest of the
season. The interesting feature is that the Great Red Spot has been joined by two little
red spots nearby. The GRS, for scale, extends almost two-and-a-half earth diameters
and is a centuries old anti-cyclonic storm system with winds measured by the Voyager
I spacecraft at nearly 350 miles per hour. Jupiter itself weighs about 318 times the
earth."

Thanks Dan!

-Tom Skilling

Brett Smith of Naperville was busy Sunday photographing the day’s thunderstorms and we
thank him for sharing his photos of the storms with us. Brett tells us the shots include a
supercell in Indiana and another rapidly developing supercell north of Naperville. Many
thanks Brett! Great shots!

-Tom Skilling

Photos courtesy of Brett Smith, Naperville, Illinois

Chicago's second 90-degree day of the year is just days away. Just one 90-degree high
temperature is on the book this year -- rare for so late into the season. Only 13 of the
80 years since 1928, at Midway Airport, have had as few or fewer 90s by June 24. There
had been five by this time a year ago, which equals the long-term average. City
residents had experienced 18 by this date in the Dust Bowl year of 1934. The 90-degree
drought this year is unusual, considering the opening 23 days of June have averaged
70.4 degrees -- one of the 10 warmest such periods of the past half century, and 35th
warmest such period since 1871.

HUMID AIR'S ADVANCE TO IGNITE TUESDAY NIGHT THUNDERSTORMS

Clouds increase Tuesday ahead of waves of thunderstorms in coming days which
threaten to deposit 1 to 3 inches of rain. The jet stream is shifting well north of the
area in typical summer fashion. It's a set-up in which light upper air winds here allow
downpour-generating thunderstorms to move slowly, a formula for generating large
rain totals.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I live in Beverly Shores, Indiana and on a few occasions around sunset I have seen a
view of the Chicago skyline that resembles a "bar code". Can you explain what is going
on?
-Patricia Kieta

Dear Patricia,
What you are seeing is a magnification of Chicago's shoreline resulting from
a temperature inversion where warm air is layered above colder air found
near the surface of the lake. This inversion bends rays of light from the
city back toward the colder, denser air above the lake creating a "towering"
effect where objects become magnified and stretched like high walls. This
type of mirage is sometimes called a Fata Morgana (Italian for Morgan the
fairy). The name comes from the fairy-like castle mirages that frequently
appear over the Strait of Messina separating Italy and Sicily. Morgana was
the mythical fairy who lived in a crystal palace beneath the waves.

Our meteorological colleague Richard Koeneman, who resides amid the natural
splendor of the Smoky Mountains in western North Carolina and whose remarkable
climatological analyses grace the pages of this blog and the Chicago Tribune weather
page on a daily basis, shares these spectacular shots with us---the top taken a
month ago and the bottom snapped Monday---illustrating the emergence of lilies
outside his home in the mountains near Asheville. Richard reports the area continues
in the midst of a terrible drought, a fact not at all obvious when you look at the the
splendor of the region! Thanks for sharing these with us Richard!

-Tom Skilling

Photo courtesy: Richard Koeneman

Tom Skilling predicts warmth and humidity ahead for the next couple of days. But watch out for possible thunderstorms on Wednesday!

Also, find out how many 90* weather days we will have for the end of the month.

What a sight! Kasey Ignarski of Orland Park photographed this rainbow over Wrigley Field
Sunday.

"Anviling" thunderstorm Sunday afternoon as viewed from Lake Forest around 4 pm

Adam Polinski was at his son’s baseball game Sunday when this thunderstorm caught his
eye. He pointed the storm out to Les Ashton, also at the game, who snapped this photo of
the towering thunderhead (cumulonimbus cloud). Rain, thunder and lightning followed
shortly after, Adam reports. The “anvil” appearance of this cloud’s top—because it is
unobscured by surrounding surrounding clouds—makes this a fascinating sight. Thanks
for calling this terrific photo to our attention Les and Adam and we hope your son’s team
won!

-Tom Skilling

Photo courtesy of Les Ashton, Mt. Prospect, Illinois

Sheela Prasad photographed Sunday's thunderstorms--including the concentrated shafts of rainfall often obvious as well defined streaks of gray extending from the base of the cloud--in northern Lake County, Illinois during a drive to Wisconsin. Man thanks for sharing these shots with us, Sheela!

-Tom Skilling

Photos courtesy of Sheela Prasad of Vernon Hills

Patrick Henson took shares these Sunday photos from Chicago's Roger's Park community
with us and comments in his e-mail to us that the hailstorm responsible went on longer
than any he remembers the 44 years he's lived in Chicago. Great shots--thanks Patrick!

-Tom Skilling

Photos courtesy of Patrick Henson, Rogers Park-Chicago

Scattered showers and thunderstorms popped up in an irregular pattern Sunday over the
Chicago area and northwest Indiana. There were many reports of pea- to quarter-size
hail. Half-inch hail covered the ground at 5:30 p.m. just south of Evanston. This
unstable air, associated with low pressure centered well to the north and east of Lake
Huron in Canada's Quebec province, moved to the east overnight.
Light northerly winds on the front side of cool high pressure over the western Great
Lakes will prevail over Chicago today with inland heating conducive to the setting up of
a lake breeze, resulting in cooler shoreline temperatures this afternoon.
DOWNPOURS COULD BRING MORE WORRY
A change in the upper-level jet stream pattern will open the gates for warm, humid air
to flow into the Midwest starting Wednesday. Weak warm and cold fronts will not
influence temperatures greatly, but will add instability to an already unstable
atmosphere. Frequent periods of showers and thunderstorms are likely, beginning later
Wednesday and continuing through Friday. Heavy rain with some of these storms could
bring more worry to residents of Iowa, Missouri, Wisconsin, Illinois and Indiana, who
are weary of battling flood-swollen rivers and streams.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
I have heard infrared light referred to as "beyond the red." What does this
mean?
Dale Halvers
Dear Dale,
The answer can be found in the year 1800. British astronomer Sir William
Herschel (1738-1822), while investigating the nature of light, moved a
thermometer through the spectrum of colors obtained by passing light through
a prism. Herschel observed that the thermometer registered higher
temperatures as it absorbed heat energy contained in the light. That outcome
was expected.
Much to Herschel's surprise, however, the temperature continued to rise as
he moved the thermometer "beyond the red" portion of the spectrum and into
the darkness. Herschel had discovered a previously unknown form of radiant
energy: invisible infrared light whose wave length lies just "beyond the
red" wavelength.

One of our regular and always wonderful picture contributors, Tracey Surface, has
checked in with us. Tracey was out in the Quincy, Illinois, area and shares with us shots
of the ongoing and tragic flooding still in progress. She arrived home in time to
photograph several of Sunday's storms as they swept the Montrose Harbor area of
Chicago. As always, terrific shots Tracey! Many thanks, as always, for sending them
along!

Photos courtesy of Tracey Surface, Chicago

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

Here's a look at some of the spectacular snapshots viewers sent us of the rainbows
seen Sunday afternoon in the wake of the day's storms. Thanks to all for your
wonderful pictures!

A view of a double rainbow from Old Town. (Photo courtesy of Jeanne Kruss)

Two photos taken near Belmont Harbor. (Photos courtesy of John Picken)

A view of the rainbow near Navy Pier. (Photo courtesy of Janet Pearson)

A double rainbow in Ravenswood. (Photo courtesy of Dan Rowley)

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

Christina Cooper of Wheaton was kind enough to show us some of the hail that fell in
Wheaton around 5:55 p.m. Sunday evening. Thanks, Christina!

Photo courtesy of Christina Cooper

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

Grant and Jennifer Bauler of Sycamore, Ill., snapped this remarkable photo a week ago
on Fathers Day 2008 and ask what causes a formation like this to form.
What we see here is a "shelf cloud." It forms as rain-cooled air gushes out of a
thunderstorm or line of thunderstorms. This cooling leads to condensation of moisture
in the air ahead of the squall and produces a bank of rolling clouds ahead of the
storm's leading edge. Winds usually increase at ground level dramatically beneath or
just ahead of shelf clouds. I think Grant and Jennifer put it best in their e-mail to us
when they wrote:

“We have seen a lot of storm fronts, but this one was pretty spooky!”

Photo courtesy of Grant and Jennfier Bauler, Sycamore, Illinois

Well put! Many thanks Grant and Jennifer.

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

Thunderstorms grow vertically through a region of declining temperatures which
dominate the lowest layer of the atmosphere -- the troposphere -- then flatten out
into what's referred to as an "anvil" (because of the similarity to the old blacksmith's
anvil) as the storm's updrafts reach into the lower stratosphere.
There, temperatures no longer fall with height -- in fact, readings begin rising. Air
parcels remain buoyant and continue rising as long as the air around them cools. This
cooling keeps the upward moving parcels lighter than their surroundings. But, once
readings steady or begin to rise with height, the upward moving air becomes heavier
than its surroundings and the ascension ceases, leading to the formation of
thunderstorm "anvils".
These wonderful photos from Michelle and Pat Slove and Aimee of Mundelein, Illinois,
depict this process beautifully and were taken Sunday afternoon around 3 p.m. looking
toward Vernon Hills. Thanks to Michelle, Pat and Aimee for sharing these with us!

Photo courtesy of Michelle and Pat Slove

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

Our friend Matt Hoelter sends us these terrific shots of Sunday's towering cumulonimbus
clouds (thunderheads) over McHenry County's Prairie Grove, Illinois. Dopper radar scans
revealed some cloud tops as high a 43,000 feet at times over northeast Illinois, northwest
Indiana and southern Wisconsin. Thanks for the great photos, Matt!

Photographs courtesy of Matt Hoelter

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

Many Chicago area residents woke up to the sound of thunder this morning. While the storms were not severe some of them did produce small hail; most of the hailstones were in the 1/4-1/2 inch diameter range. Thanks to Rob Omori of Chicago who took these storm shots from his deck near Loyola University.

Steve Kahn WGN Weather Center Meteorologist

Photos by Rob Omori

Showers and thunderstorms are expected this afternoon under the influence of a large
low pressure area east of Lake Huron in Canada's Ontario province. Steered by a strong
northerly jet stream flow aloft, cool high pressure will drift south and east out of
central Canada and hold over the Midwest through Tuesday. This will give northern
Illinois temperatures about 5 degrees below normal for the next few days. After today's
rains, a brief dry period will hopefully allow most of the area's swollen rivers and
streams to slowly fall.

WARMER, MORE HUMID AIR BY MIDWEEK

By Wednesday, the upper air pattern will change significantly with a west-to-east jet
stream flow establishing along the United States-Canada border. This will block the
southward movement of cooler Canadian air masses, and allow a gradual intrusion of
warmer, more humid air from the central and southern Plains into the Midwest. During
the last half of the week, Chicagoans should see readings average about 5 degrees
above normal along with much more humid conditions and frequent showers and
thunderstorms. Rainfall totals the latter half of the week could easily exceed an inch.

--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
While visiting Rocky Mountain National Park in Colorado, we came upon the source of
the Colorado River, and my daughter (age 9) asked how long it took water from there to
reach the Pacific Ocean.
-Steven Smith

Dear Steven,
From its source at Grand Lake in Rocky Mountain National Park, the Colorado River
winds its way 1,450 miles to the Gulf of California, an appendage bay to the Pacific
Ocean. The Bureau of Reclamation estimates that water leaving Grand Lake requires a
minimum of four to six years to complete its journey to the Gulf of California. Time
spent in several large reservoirs (such as Lake Mead behind Hoover Dam) accounts for
that extraordinarily lengthy trip. However, much of the water never arrives at the gulf. In
some recent years, all of the water as been drawn out for irrigation and municipal use.

Towering thunderstorms swept roughly half of the metro area in two waves Friday --
the first delaying the opening game of the Crosstown Classic at Wrigley Field with
downpours and peppering some northwest suburbs with hail as large as quarters.
The second wave of storms erupted mid-afternoon in 80-degree warmth and drenched
north sections of Geneva in the Fox Valley with an inch of rain in just 35 minutes. The
storms also toppled a tree across a house just southeast of Warrenville in DuPage
County.
The storms were the first to sweep the area since last Sunday. While hail and lightning
were the biggest threat posed by most storms, several generated wind gusts clocked at
45 m.p.h. in Kane County's Burlington. The largely storm-free south suburban area
hosted upper 80-degree temperatures -- including 88 degrees at Plainfield, Kankakee
and Orland Park.
SOUTHWEST WILTING IN 7TH DAY OF TRIPLE-DIGIT HEAT
Temperatures surged past 110 degrees for a seventh day Friday in parts of the
Southwest. Highs reached 117 degrees at Palm Springs and 110 degrees at Santa Maria,
both in California -- readings up to 38 degrees above normal.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Do tornadoes occur in the early morning hours? If so, why are there so few?
David Carli, Geneva High School
Dear David,
The vast majority of this nation's tornadoes occur during the late afternoon
and evening when the atmosphere is most unstable after a full day of solar
heating. After sunset the air cools and stabilizes, and the threat of
tornadoes diminishes. That being said, tornadoes have occurred at all times
of the day and night including the pre-dawn hours. At 6:10 a.m. on June 9,
1966, residents of Chicago's northwest suburbs were awakened by severe
thunderstorms that spawned an F2 tornado. The twister first touched down in
Hoffman Estates, then skipped along a 13-mile path through Arlington Heights
and Prospect Heights. The twister killed one and injured 23, and caused $4
million in property damage. Just 10 hours earlier, that same thunderstorm
complex produced a killer tornado in Topeka, Kan.

Tom Skilling and his team have identified two clusters of thunderstorms that are developing in the Chicago-land region. Some suburbs are even experiencing hail. Watch today's edition of Before the Forecast for the full scoop!

Tyler Christiansen shows us these ominous-looking and clearly wind-tossed clouds
which accompanied Friday's storms into Elgin. Great shots, thanks Tyler!

Photos courtesy of Tyler Christiansen of Elgin

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

Matt Seegmiller of Algonquin says while a majority of the hail which hit with Friday
morning's 20-minute hail storm, several larger hailstones -- like the one pictured
below -- hit as well. He tells us:

"I watched the storm roll through as I was standing in my garage, and I heard a loud
noise hit what sounded like my neighbor's adjacent roofline to our townhouse. I went
out and looked around and noticed this large softball-sized hail ball that had landed in
our yard!"

"I measured it at four and 1/2 inches wide by three and 1/2 inches high. This was
probably only 1 or 2 hail pieces of this size to fall out of millions of pieces that fell in
the area this morning. I was glad it hit the grass in the yard and not my car!"

Photo courtesy of Matt Seegmiller, Algonquin, Illinois

You are so right, Matt! Thanks for the great photo!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Hail, ranging from pea to quarter size in size, pelted Chicago's northwest suburbs
Friday morning, prompting severe thunderstorm warnings for a time. A second batch of
storms is erupting at the time of this posting (3:20 p.m. Friday afternoon) and has led
to additional severe thunderstorm warnings over Chicago's west and northwest
counties.
The southeastbound morning storms emanated from cloud tops radar scanned at up to
38,000 feet in height.

In these terrific photos, Scott Withycombe captured the hail which was bounding off the
ground at times around 11 a.m. in the Algonquin and Lake In the Hills area. Many
thanks to Scott for sharing these shots with us!

Photos courtesy of Scott Withycombe in Algonquin

A note: The storms which produced the hail pictured here arrived in the city just before
midday and, though in a weakening phase, produced downpours which delayed the
Crosstown Classic baseball game between the Cubs and White Sox for a time early
Friday afternoon.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Our thanks go out to Judy Wiggins and Katie Connolly of Palos Park, Illinois for sending us this "post-card" picture of a Chicago sunset taken aboard the Tall Ship Windy off Navy Pier last month.

Steve Kahn WGN Weather Center

Temperatures surged above 80 degrees for the 14th time Thursday in the midst of one
of the driest June air masses here in three years. Slowly retreating flood waters still
cover areas adjacent to the Fox and Rock Rivers into next week. But that had little
impact on relative humidities here which by 3 p.m. Thursday had dropped to 23
percent. There hasn't been a lower relative humidity in June since the 18 percent
reading recorded June 22, 2005. High temperatures return to the 80s Friday and
Saturday--but the 2008 tally pales in comparison to the 30 days of 80-degree or
higher readings a year ago. The city had seen only one 90-degree-plus high to date --
less than the five considered normal.

HEAT'S RETURN NEXT WEEK COULD PROVOKE NEW T-STORMS

Summer-level warmth surges back into the area as June enters its final days the middle
and end of next week. It's a development that could produce regular clusters of
thunerstorms. It was another active night across the western Plains on Thursday. More
that 235 reports of severe weather were logged by the Storm Prediction Center in
Norman, Okla., including 185 reports of hail.

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

Dear Tom,
How many positive and negative lightning bolts are there?
Sharon Schutz
Dear Sharon,
We can separate lightning bolts into two broad categories: within-air flashes and
ground strikes. Meteorologist and former Chicagoan Dr. Walter Lyons estimates that in
the United States the ratio of flashes that do not strike the ground to those that do is
about 4-1; that is, 80 percent to 20 percent.

The installation of a nationwide lightning detection network in the early 1990s enabled
researchers to count lightning bolts accurately, and the numbers are stunning. Just in
the U.S., the tally is 100 to 125 million bolts annually, of which about 22
million are ground strikes.

Of those 22 million, 90 percent are termed "negative," meaning the flow of electric
current is from cloud to ground, and 10 percent are "positive," current flowing from
ground to cloud.

Tom Skilling talks about the beautiful weather for Thursday, and the changes to come for the coming days. Tom also takes Before the Forecast viewers on a behind-the-scenes look at his weather watch maps. Join the ride, and watch today's edition of Before the Forecast!

Check out these beautiful shots of Wednesday evening’s (June 18) full moon above
the fountains on Northwestern University’s Evanston campus! They were
photographed by Vincent Giovannone. Thanks for sharing these with us, Vincent!

Tom Skilling

Photos courtesy of Vincent Giovannone

The clock may be ticking toward summer—the season gets under way at 6:59 p.m.
Friday—but you wouldn’t have known it late Wednesday. Temperatures across a
westward moving lake-breeze front varied so widely the front was discernable to area
weather radar despite the lack of precipitation with it. While most cool fronts powered
by breezes off Lake Michigan make it only 20 or 25 miles inland in mid June,
Wednesday’s traveled more than 50 miles in. By evening, temperatures near the lake
had tumbled into the 50s even as 80-degree readings lingered to the west. The
strength of this front was a product of Lake Michigan water temperatures 12-degrees
cooler than a year ago—a leftover from Chicago’s chilly May.

HAIL THE SIZE OF SOFTBALLS BOMBARDS THE PLAINS WEDNESDAY
More than 5 dozen reports of hail accompanied thunderstorms across eight Plains
states. Hardest hit was an area southeast of Westerville, Neb., and just north of
Center, N.D., where hail the size of softballs (4.25 inches in diameter) fell. Record
heat continued in the Southwest with Palm Springs, Calif., setting a temperature
record of 115 degrees.

Dear Tom,
Do bursts of heavy rain called "rain gushes" follow thunder?
Richard Samall
Dear Richard,
University of Florida lightning expert Dr. Martin Uman says, "Observers of
thunderstorms, from antiquity to the present, have noted that a heavy gush of rain
often reaches ground a minute or two after a lightning flash and its accompanying
thunder." He explains that questions about the relationship between lightning, thunder
and rain gushes were finally resolved in the 1960s, when radar observations of
precipitation in clouds before and after lightning confirmed that, in some cases, a gush
followed the flash.

Researchers postulate that cloud droplets near a lightning channel and its many
branches acquire such intense charge that they repel each other, flying outward and
colliding with non-charged drops, thereby growing large and falling as a rain gush.

Imagine this coming at you! These remarkable photos taken this past weekend in
Fargo, North Dakota, have been relayed to us by Michael Lawson, who interned
recently with us here in the WGN Weather Office. Michael had traveled from Grand
Forks where he is a meteorologist at Meridan Environmental Technology to Fargo,
North Dakota to attend a independent league baseball game. He reports this storm
spawned a twister before sending its ominous looking shelf cloud Fargo. Michael
includes a shot of a cold air funnel taken last week in North Dakota by a collague.

Tom takes his Before the Forecast viewers on a behind-the-scenes look at his weather watch maps. Join the ride, and watch today's edition of Before the Forecast!

Thanks to Gary Loberg who sent us this pictures of the menacing clouds that accompanied the wave of thunderstorms that swept the Chicago Metropolitan area during the early morning hours.

All photos by Gary Loberg

Steve Kahn WGN Weather Center Meteorologist

The weather's turned beautiful in recent days and still water is on display everywhere in
the Midwest. Forecasts suggest the Fox River, which began falling Tuesday in
Wisconsin, is to crest later this week and only slowly retreat this weekend and early
next week. Water levels on parts of the flooding Rock River are at their second highest
levels on record.

Even Lake Michigan is responding to the copious rains of recent weeks. The U.S. Army
Corps of Engineers reports water levels are 3 inches higher than a year ago. That
doesn't sound like much. But, each inch the Lake Michigan rises represents an increase
of 390-billion gallons of water. Precipitation across the 45,000 square mile drainage
basin of Lake Michigan has averaged 181% normal since June began and the lake's
volume has risen 1.17-trillions gallons over the past year.

BLISTERING HEAT BLAZES ACROSS THE SOUTH

The hottest weather this season is baking the Southwest. Phoenix topped out at
113-degrees -- one degree shy of the record Tuesday while Tucson hit 109-degrees.
The warmth threatens to expand east next week and could signal a warm-up here
Wednesday and beyond.

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

Dear Tom,
I love hot weather. Has the city even recorded back-to-back 100 degree days?
John Cosgrove
Dear John,
Chicago does not experience a lot of 100 degree days but the city's official
station has recorded consecutive 100 degree days on 12 occasions since
records began in late 1870, including three 100s in a row in 1911 and 1947.

However, these numbers don't tell the entire story because during the
intensely hot "Dust Bowl" summers of the 1930s the city's official
thermometer was located very close to the cooling breezes of Lake Michigan.

In the summer of 1934, inland Midway Airport logged six consecutive days
above 100 degrees from July 20-25, including a torrid 109 degree high on July 23. Two
years later, the summer of 1936 produced eight straight days in the 100s from July
7-14. The city's last back-to-back 100s were July 13-14, 1995 during a deadly heat
wave that killed more than 750 people.

Scenic Galena in northwest Illinois is always a treat for the eyes. But Don and Jan
Porter share this beautiful Monday, June 9 sunset with us. The photo was taken
around 8:45 p.m. that evening. Thanks Don and Jan!

-Tom Skilling

Photo courtesy Don and Jan Porter of Galena, Illinois

Temperatures for this week will be below normal with above normal temperatures for the weekend. To find out more, watch Tom Skilling's Before the Forecast.

It was only five days ago that area heat enthusiasts were relishing a temperature of 91
degrees. Dramatic changes in the upper atmosphere, including the reappearance of a
dome of warm air aloft to the west of Greenland over the Davis Strait -- a pattern
behind Chicago's persistent winter and spring chill -- have this week's weather on a
much different track. The pattern produces northwest steering winds aloft that tug cool
Canadian air south across the Midwest. Lacking the moisture delivered by south winds
from the Gulf of Mexico, this atmospheric set-up greatly limits thunderstorm
development -- a blessing for Chicago-area residents who have been forced to
contend with flooding in the past week. Only the Fox River in this area has yet to crest,
a benchmark to be reached Wednesday morning.

COOLEST WEATHER HERE IN TWO WEEKS

Monday's 72-degree high was Chicago's coolest since the 69-degree high June 3 and
the second chilliest daytime high to date this month. Temperatures over the coming
five days (through Saturday) will average 18 degrees cooler than the same period a week
ago. But warmth and humidity are to stage a comeback this weekend.

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

Dear Tom,
The other day when I was out running, it began to drizzle and I noticed a strong smell
of rain in the air. What causes that odor?
DeeDee Rossman

Dear DeeDee,
There are a number of explanations for the unique smell of rain. The vegetation of an
area appears to contribute, with the reaction between moisture and high humidity on
certain substances in plants releasing odors into the air. For example, pine forests
release terpenes, a substance that is found in medicine and perfumes. Moisture,
warmth and lowering pressure, all forerunners of rain, hasten the release of fragrant
molecules from plants. As rainwater soaks into soil particles, it pushes aromatic gases
produced by streptomyces, a soil bacteria, into the air, producing an earthy smell.
Falling raindrops also kick up particles from blacktop and concrete that add to the
potpourri of odors that we like to describe as the smell of rain.

After a well-deserved trip, Tom is back in business with his daily Before the Forecast webcast! Check out what's in store for Chicago weather this week.

Bill Gratzl provided us with these breath-taking pictures taken at 41,000 feet over Wichita, Kansas last week. The thunderstorm tops were estimated to be around 55,000 feet and the photographed thunderstorml produced at least one funnel cloud report.

Thanks to Tom Wedin Sr. of Wonderlake, Illinois for this stunning picture of what used to be Lake Delton at the Wisconsin Dells. The lake drained after heavy rainfall eroded the river banks.

Mary Anne Best of Remington, Indiana forwards these photos taken on I-65 in Sunday afternoon by Jennifer Hupke of Griffith, Indiana. Jennifer’s photos, originally sent to my meteorological colleague Michael Prangley of WLFI-TV, appear to depict gustnadoes—tornado-like whirls of debris generated by the powerful outflow of air roaring out of Sunday’s severe thunderstorms. Her photos parallel those we’ve posted from Paul Hadfield in central Illinois. In her e-mail to Michael, Jennifer comments:

“I took pictures, and after the fourth shot I took we grabbed our bags (go figure) and ran from the car to take cover in a ditch because it was right on top of us- we did what we were supposed to but it was hard to leave the "safety" of the car to brave the elements outside.”

Many thanks to Jennifer Hupke, Michael Prangley and Mary Anne Best for sharing these photos with us!

Tom Skilling

Photos taken on I-65 Sunday by Jennifer Hupke, Griffith, Indiana

From east of Macon, Illinois come these remarkable shots from Paul Hadfield of
gustandoes—the low-level tornado look alikes--which spung up ahead of the gust
front produced by Sunday afternoon’s powerful eastbound thunderstorms. Many
thanks to Paul for the eye catching photos!

-Tom Skilling

Amanda Pickett, who has so frequently shared photos with us, sends along these
spectacular shots from northwest Indiana of Sunday afternoon’s (6/15) powerhouse
thunderstorms which swept areas mainly south of Chicago. They produced a number
of reports of severe weather and erupted after morning storms which hammered
sections of the Chicago area with downpours and wind gusts clocked to 55 m.p.h. at
some points on the city’s lakefront. Amanda’s shots clearly depict the rain shaft
produced by one of the thunderstorms and a cloud to ground lightning strike. She
reports one lightning bolt hit within 20 feet of her home. Thanks Amanda!!

-Tom Skilling

This dramatic cloud to ground stroke hit Navy Pier with Sunday's first wave of thunderstorms. Photographer Jim Bayne shares this photo with us. It was taken around 8 a.m. Sunday morning. Thanks Jim!

-Tom Skilling

Photo courtesy of Jim Bayne, Chicago

Thanks to Jeremy Gissel who sent us this great lightning shot taken in Yorkville around 2:30 p.m. Sunday afternoon.

Photo by Jeremy Gissel

Steve Kahn WGN Weather Center Meteorologist

It's often the case that persistent and extreme weather in one region of the United
States is balanced by persistent and extreme, but opposite, weather in another portion
of the nation. While many residents of the Midwest struggle to cope with
unprecedented rainfall and record river flooding, residents in the western third of the
nation desperately wish the skies would open. They've been locked in a withering
drought that, in some locations, is now in its seventh year. As of June 13, 13 large
forest fires and literally hundreds of small fires were in progress from California to
Colorado. Flow rates in large western rivers (like the Colorado River) are nearing
historic lows, and, after a very dry winter and the driest May on record in California,
Gov. Arnold Schwarzenegger has declared an official statewide drought, the first such
designation since 1991.

'DRY THUNDERSTORMS' TORCH WESTERN FORESTS
Only very rarely are lightning ground strikes responsible for fires in the normally
well-watered forests of the eastern United States. It's a different story in the West.
There, thunderstorm rainfall, even in the best of times, is of limited extent, and
lightning often strikes outside a storm's precipitation area.
--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
Someone told me you actually predicted the New Orleans disaster with
Hurricane Katrina here in this weather column. Is this true?
Anton Smithson
Dear Anton,
It is not true, but this column did speak of the vulnerability of New
Orleans to the ravages of hurricanes two years before Katrina devastated the
city. The following information appeared in this column on Oct. 4, 2003:
"The National Hurricane Center ... advises that New Orleans is considered to
be the U.S. city most vulnerable to hurricane storm surge."
Katrina came ashore on the Louisiana and Mississippi coast on Aug. 29, 2005,
as a strong Category 3 hurricane (on the 5-point hurricane intensity scale).
It brought 127-m.p.h. sustained winds and an unprecedented storm surge of 15
to 20 feet on the Louisiana coast, and up to 28 feet on the Mississippi
coast.

Impulses of energy zipping from northwest to southeast across the Midwest on Saturday
triggered scattered thunderstorms just where more rain wasn't needed: eastern Iowa and
southern Wisconsin. Many locations received no rain, but a few spots just west of Madison
and also near Iowa City picked up 1 to 2 inches of unwanted rain. A few of those
thunderstorms swept across Chicago's northern suburbs, though with much less rain.
That pattern of scattered but locally strong, hit-or-miss thunderstorms continues today
across the Chicago area as well as Illinois and surrounding states. Cooler, drier air arrives
late Sunday and the region dries out, at least temporarily.

LAST YEAR’S FATHER’S DAY WAS HOT

Today's warmth won't challenge the 91-degree Father’s Day reading registered here last
year, but thunderstorms might threaten his picnic. Storms will affect 50 percent of the
Chicago area, but there will be several rain-free hours even where storms do hit.

Dear Tom,
We winter in Naples,Fla., and love viewing the beautiful sunsets over the Gulf of Mexico.
Where in the world is the sun rising when we see it set?

Ted and Diane Olsen, Lake Forest, Ill.

Dear Ted and Diane,

We posed your question to Dan Joyce, astronomer at Triton College's Cernan Earth and
Space Center. He informed us that when the sun is setting in Naples, it is rising in the
eastern Indian Ocean, west of Australia, at a point just as far south of the equator as
Naples is north of the equator (26 degrees). The exact point is precisely halfway around
the globe from Naples (180 degrees longitude away).

When the sun is setting in Chicago (longitude 88 degrees west, latitude 42 degrees
north), it is rising at a point in the southern Indian Ocean about 1,500 miles southwest
of Perth, Australia. That point lies at longitude 92 degrees east, latitude 42 degrees
south).

"Water flowing into the Chain is exceeding water flowing out," said Mike Warner,
Executive Director of the Lake County Stormwater Management Commission, speaking
of the increasingly serious flood situation on the Chain O' Lakes in northwest
metropolitan Chicago.
Even though heavy rains spared the immediate Chicago area Thursday and Friday, rain
totaling 3-5 inches swamped the headwaters of the Fox and Des Plaines rivers in
southern Wisconsin, bringing 10-day rain totals there to an overwhelming 10-16
inches. All that water is draining relentlessly south into Illinois. And so, rivers in
northern Illinois continue to rise today even as the sun shines.
In the East, a second day of modestly cooler temperatures further blunts a deadly early
summer heat wave (blamed for at least 30 deaths) that extended earlier this week from
Georgia to New England.
RENEWED RAIN THREAT ON SUNDAY
A new weather disturbance sweeps into the Midwest on Sunday, accompanied by
potentially vigorous thunderstorms. This system, unlike those that produced
unprecedented rains in the preceding two weeks, is moving rapidly and
rainfall-generating moisture available to it is limited.
--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
Who activates tornado sirens in a town?
Sandra Browning, Niles
Dear Sandra,
In the Chicago area, the decision to sound tornado sirens is made by
individual communities. The Chicago National Weather Service (NWS), which
issues tornado warnings in northeast Illinois, has no control.
NWS Warning Coordination Meteorologist Jim Allsopp says, "Procedures to
sound sirens vary from community to community. The sirens can be set off at
the request of village officials such as mayor, police or fire chief, or an
emergency management coordinator."
A standard criterion for sounding sirens is the report of a tornado or
funnel cloud from a reliable source such as a trained spotter, police
officer or firefighter, and usually within a few miles of the town. Allsopp
advises that, "NOAA weather radio is the best way to get warnings direct
from the NWS."

Now that there's a break in the storms, see what Tom sees from his perch in Alaska for today's Before the Forecast. He'll be back in Chicago on Monday!

When this picture was taken Thursday at the Quaker Oats plants in Cedar Rapids, Iowa
these trucks were partially submerged. Just 24 hours later they are totally under water.
Many homes have water up to their rooftops. Looking out at downtown Cedar Rapids all
that is visible is flowing water and the tops of light poles. Many businesses have been
closed.
--By Steve Kahn, WGN Weather Center Meteorologist

The last thing Midwesterners want to hear is that more rain and more severe
thunderstorms are on the way. For them, the forecasts contain both good news and bad
news. A cold frontal boundary, the transition zone between cool air to the west and hot
air to the east -- and a fertile breeding ground for t-storms -- stretches from
Oklahoma to Wisconsin. It's been there for three days, and so have the storms. The
frontal zone is finally shifting southeast and its associated storms will also be shifting
southeast.

Severe storms continue to be a threat today, especially south and east of Chicago, but
excessive rainfall and unprecedented flooding are now affecting far more people. Rains
will be diminishing from west to east across Iowa, Wisconsin and northern Illinois
today (the good news), but Indiana, southern Illinois and Michigan are next in line for
the rains (the bad news). Those areas, too, desperately want dry weather.

CHICAGO'S 90-DEGREE SEASON BEGINS

It's two weeks late, but Chicago logged its first 90-degree day of the season on
Thursday: 91 degrees. On average, that first occurrence lands on May 29. For those who
are counting, the city's annual tally of 90-degree days is 24 at Midway Airport and 11
days in (lake-cooled) downtown Chicago.

--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
Is it possible for a drought to happen in the winter? Has it happened?
Katie Stevens (age 10), Tinley Park, Ill.

Dear Katie,

Drought (extreme dryness due to lack of precipitation) can occur at any time of the year
-- winter included. But its effects are most noticeable during the period from April
through September when actively growing plants need water.

A drought that began in January of 2007 in the southeastern United States continues
today. The Chicago area suffered through harsh winter droughts in 1919-20, 1930-31
and 1962-63.

A winter drought usually coincides with a lack of stormy weather, which urban
residents welcome. But they fail to realize that winter precipitation is vital because it
recharges soil moisture in preparation for the next growing season.

Melissa Perino has sent us two photos of last Saturday evening's tornadoes. This twister touched down between Braceville and Essex. The pictures were taken on the family's farm in Braceville.

Photos by Melissa Perino

Steve Kahn WGN Weather Center Meteorologist

Thunderstorms will be rolling into the Chicago area tonight, and they might be
severe. Heavy rains, too, seem likely. The same storm system battered the Plains with
three dozen tornadoes, one of which reportedly claimed four lives at a Boy Scout
camp near Little Sioux, Iowa.

When the eastern United States is warm, the West is often cool, which has been the
case in recent days. Cities like New York, Washington and Charlotte have set heat
records while the West has shivered.
Sporadic snows in excess of 15 inches have buried higher elevations of the Northern
Rockies and the Cascades.

UNPRECEDENTED FLOODING IN IOWA

Cedar Rapids, located on the Cedar River, is among Midwestern cities hardest hit by
flooding. Officials there have expanded mandatory evacuation in that city to areas
matching its 500-year flood-plain map. The Weather Service's River Forecast Center
in Chanhassen, Minn., predicts a flood crest of 24.5 feet on the Cedar River, 4.0 feet
above the previous record flood there in 1929.

Dear Tom,
Do thunderstorms that grow higher than usual also tend to be more severe?

Ronny Nauta

Dear Ronny,

A general relationship between thunderstorm height and thunderstorm severity does
indeed exist: The higher the cloud top relative to other thunderstorms in the air mass,
the greater is the storm's severity. We measure thunderstorm severity by the strength of
its straight-line winds, the size of its hail and its ability to generate tornadoes.

Thunderstorm top height is the single most telling factor in storm severity, but speed
is also critical. Fast-moving thunderstorms (40 m.p.h. or greater) tend to be more
severe than slower-moving storms. Note that lightning production and heavy rain, even
flood-producing rain, are not defined to be severe criteria even though such aspects of
thunderstorm weather are dangerous and potentially deadly.

Summer's start is not an astronomical event, but it's easy to think so. After all, the
summer solstice (an astronomic event that occurs this year on June 20) marks the official
start of summer. In the atmospheric sciences, however, summer is the three- month
period that began on June 1. But climatologically, the warmest quarter of the year at
Chicago is the 91-day period that begins today. With an average temperature of 73.5
degrees, June 11 through Sept. 9 is Chicago's summer -- its warmest 91 consecutive
days.

JUNE: WETTEST MONTH IN WETTEST SEASON

Summer is also Chicago's wettest season and, at Midway Airport, June is summer's (and
the year's) wettest month. Normal June rainfall, 4.16 inches, accounts for 11 percent of
the city's annual total. With 4.00 inches as of June 10, nearly all of the full month' s
normal allotment has already come down.

--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
I've read about the "green flash" being seen in southern Florida. Fact or fiction?
Helen Baker, Naperville, Ill.

Dear Helen,
The "green flash" is real. It is a momentary flash of green light emanating from the
upper rim of the rising or setting sun at the moment it crosses the horizon.

Widely thought to be visible only in the tropics, the green flash can be seen anywhere in
the world, and most easily from a vantage point with an unimpeded view of the horizon,
such as over a large lake or ocean.

Sunlight passing through the atmosphere is bent upward, and the bending is greatest
when the sun is on the horizon. The shortest wavelengths of light (blue and green) are
bent the most, so they are the first colors seen on the rising sun and the last as it sets.
Blue wavelengths are removed by atmospheric scattering, leaving the green
wavelengths visible for the flash.

We thank our many readers and viewers for sending in pictures from last weekend's tornadoes. Pilot Anson Mount took these photos Saturday night during a test flight up to Green Bay, Wisconsin. While returning back to Chicago, he encountered a line of storms which had prompted a tornado warning near Rockford. The photos were taken roughly over the Waukesha area.

Thanks for sharing these with us Anson!


Bill Snyder--WGN weather producer

All photos by Anson Mount

Geographer Dr. George Kimble, in his book, “Our American Weather,” wrote: “Of all
the months of the year, none has been so widely sung, or greatly loved, as June—and
with reason. Almost everywhere, it is a wholesome month.”
That generalization might be true, but many Americans will challenge Kimble’s
optimistic assessment today. Just in the Midwest, the first nine days of June have
brought record rains (and record flooding), several tornadoes to southern Wisconsin
and northern Illinois and repeated waves of severe thunderstorms with damaging
winds.

RECORD JUNE RAINS

Lyons, Ohio, (32 miles west of Toledo) reported thunderstorm wind gusts measured
at 117 m.p.h. on Monday. An incredible 9.20 inches of rain swamped Milwaukee in
the June 1-9 period, fully 893 percent above normal and enough to make June 2008
the third-wettest June on record there, even with no additional rain during the
remainder of the month. Chicago, bypassed by the region’s heaviest rains, has
nonetheless registered impressive June totals. Midway Airport observer Frank
Wachowski reports June 1-9 rainfall of 3.97 inches, the second greatest total for that
period (only behind 6.29 inches in 1993).

Dear Tom,
My wife and I were married on June 10, 1967 during terrible thunderstorms. City
viaducts were flooded and the church lost power. What exactly happened that
afternoon?

Thanks, Mary Jane and Pat Clifford, Chicago

Dear Mary Jane and Pat,

Your wedding took place during one of the most intense rain events in Chicago weather
history. A record 5.20-inch deluge swamped the Loop in just a two-hour period that
afternoon, and the aftermath was widespread major flooding. Water flowed six inches
deep through Loop streets; many basements flooded. The total precipitation from the
storm was 6.09 inches downtown. O'Hare International and Midway Airports registered
about 3 inches. High water closed city expressways and thousands lost power. In
addition to the heavy rainfall, tornadoes tore the roofs off houses in Romeoville and
caused damage at the Galt Airport in McHenry County. The storms were responsible for
two deaths in the Chicago area.

Thanks to Amy Mckinney of Plainfield for this great tornado shot.

Photo by Amy Mckinney

Dan Heath of Dyer, Indiana sent along this great shot of the twister visible from this subdivision.

Photo by Dan Heath of Dyer Indiana

Steve Kahn WGN Weather Center Meteorologist

David Mayhew, a regular contributor to this blog, has provided some stunning photographs of the twisters that struck this area on Saturday evening June 7.

All photos by David Mayhew

Steve Kahn WGN Weather Center Meteorologist

As if Saturday's severe thunderstorms and tornadoes weren't enough, the Chicago area
was expected to take another pounding Sunday night with waves of powerful storms
sweeping through. And it's not over yet -- but the end is in sight. The atmosphere
remains primed for yet another round of severe weather Monday, especially in the
afternoon, but cooler, less humid and more stable conditions finally promise quiet
weather by Tuesday. Until then, the possibility of flooding will add to our weather woes.
Recent heavy rains have left area rivers bankfull (or overflowing), and additional rain will
exacerbate the high-water situation. The Chicago area remains under a flash flood watch.
SATURDAY'S LOCAL TORNADOES
The National Weather Service confirmed the occurrence of six tornadoes in southwestern
metropolitan Chicago between 4 and 7:30 p.m. Saturday: two in northeast Livingston
County, three in southwest and central Will County, and the large, long-track tornado that
cut a 60-mile path from Odell (Livingston County) to Lansing (southern Cook County).
Further information can be found at the National Weather Service-Chicago Web site
at www.crh.noaa.gov/lot.
--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
Can you provide proof that it snowed in the Chicago area on the 4th of July
in the early 1970s? I remember watching fireworks at Deerfield High School
and it snowed. My mom remembers it, too.
Cheryl Fayne
Dear Cheryl,
The proof that you are looking for does not exist because snow, even a few
wet snowflakes, has never been observed in the Chicago area on July 4, or on
any day in July or August.
That fact is borne out by unofficial weather records assembled from several
observation sites in northeast Illinois during the period 1830-1870 and from
Chicago's official weather data from 1871 to the present. Those records
constitute a period of 178 years of absolutely snow-free Julys and Augusts!
July 4th, 1972, was downright chilly (high/low temperatures of 66/49
degrees), but dry: no precipitation at all. Sometimes our memories play
tricks on us.

SHELF CLOUD IN NORTHERN INDIANA ALONG I-65 SATURDAY

Photos by Shelby Pealer

These stunning photos of a shelf cloud were taken Saturday along Interstate-65 in northern Indiana. A shelf cloud is a low-level wedge-shaped cloud attached to the convective storm's cloud base. It forms at the leading edge of a thunderstorm along the gust front. Many thanks to Shelby and Anne Pealer of Naperville for sending us these outstanding shots.

Steve Kahn WGN Weather Center Meteorologist

SATURDAY NIGHT STORM DAMAGE NEAR RICHTON PARK

All photos by Barbara Gomoll

Saturday evening's tornado did major damage to George and Barbara Gomoll's yard near Richton Park. The storm struck there just before 6:25 p.m. Fortunately no one was hurt and there was no damage to their house or cars. At least 50 trees on the property were damaged including several that were completely uprooted.

Steve Kahn WGN Weather Center Meteorologist

WEEKEND SEVERE WEATHER-ROUND TWO SUNDAY AFTERNOON'S STORMS

All photos by Carolyn Szepanski

The Chicago area was raked by another round of violent weather Sunday afternoon as waves of severe thunderstorms moved across the region. The photos below were taken by Carolyn
Szepanski in Whiting, Indiana. Carolyn estimates that winds topped 80 m.p.h. and visiblity dropped to less than 100 yards in the torrential downpours. As the storm passed across Lake Michigan it formed a brief waterspout and there also appeared to be a brief tornado touchdown at the BP refinery.

Steve Kahn WGN Weather Center Meteorologist

THE LAST STAGES OF SATURDAY'S TORNADO

Photo by Steve H.

The picture was taken just before 7 p.m. Saturday evening June 7 in Lansing , Illinois near the intersection of I-80 and Burnham Avenue by Steve H. At this point the tornado was in its dissipating stage. Steve reported that the funnel's rotation was quite apparent and the storm was moving to the east at about 25-30 m.p.h. The area lost power when the storm hit and it was finally restored about 8:30 a.m. this Sunday morning.

Steve Kahn WGN Weather Center Meteorologist

During a period of nearly two and one half hours at least six tornadoes struck in areas south of Chicago. The first twister was first sighted near Odell in northeast Livingston County just after 4:30 p.m. and the last one was seen in Lansing in far southern Cook County shortly before 7 p.m. The tornadoes were widely photographed and here are some of the first pictures that we have received at the WGN Weather Center. Our thanks to Ken, Barb and Bob Garst and Ron Smierciak for sending us these dramatic pictures.

Steve Kahn WGN Weather Center Meteorologist

TORNADO NEAR MONEE

Photo by Bob Garst

TORNADO IN LANSING

Photo by Ron Smierciak

Photo by Ron Smierciak

Photo by Ron Smierciak

After tornadoes hit Saturday afternoon and evening, another round of thunderstorms,
some possibly severe, appears on tap today. Strong southerly winds wrapping around the
backside of high pressure centered over the southeastern U.S. continues to pump very
warm, humid air north into the Midwest and Great Lakes. Thunderstorms could pop up
almost anytime, but the peak heating afternoon and early evening hours appear most
likely. The National Weather Service Storm Prediction Center has projected a wide area
from the southern Plains to the western Great Lakes, including northeast Illinois and
northwest Indiana, for a chance of severe storms today.

RELIEF IN HEAT AND HUMIDITY IN SIGHT

A cold front is expected to move through the metro area Monday, preceded by showers
and thunderstorms, followed by a cooling less humid northwest flow. Hot, humid air is
forecast to briefly return midweek, peaking Thursday before the arrival of another cooling
cold front Friday. A cooler, less humid air mass should then hold through next weekend.

--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
I have been keeping records of the pollen count for many years, and the pollen level has
been increasing. What weather factors are causing this?

--William Sanders, Chicago

Dear William,

It's not the weather but rather higher levels of carbon dioxide in the atmosphere that
have markedly increased plant growth rates, including ragweed (the source of pollen
that triggers hay fever). Since 1900, atmospheric carbon dioxide has increased 30
percent, from 294 parts per million (ppm) to 380 ppm now. In response, ragweed has
doubled its pollen production since 1900. Dr. Paul Epstein of Harvard University's Center
for Health and the Global Environment says, "This carbon dioxide stimulation of plants
has a side effect for public health. The hyper-production of pollen can cause hay fever,
conjunctivitis and can exacerbate asthma."

Many areas of northeast Illinois were storm-free Friday. Where the storms did hit,
significant wind damage occurred. Thunderstorms moved at 55 m.p.h., and this
movement, combined with wind gusts out of the storms, resulted in localized 75 to 80
m.p.h. winds. Power lines and trees were downed, and a grain bin tipped over in
Lindenwood at Davis Junction in Ogle County. Extensive wind damage also occurred in the
Marengo area in McHenry County. Tornadoes were reported around 2:30 p.m. in Poplar
Grove and Capron in Boone County.
SOUTHERLY FLOW CONTINUES
Warm southerly flow and high humidity will continue over northern Illinois this weekend.
With temperatures forecast to approach or even exceed 90 degrees both Saturday and
Sunday, this weekend could be the city's warmest since last July 7-8.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
I have heard you say, "Afternoon highs ran 17 degrees below normal." Those
temperature swings are normal for the Chicago region. The correct comment is
that "Afternoon highs ran 17 degrees below average."
Charles Rosenfelder, Glen Ellyn
Audrey Roen, Oak Park
Dear Charles and Audrey,
Meteorologists (and others in the atmospheric sciences) define "average" and
"normal" in ways that are somewhat different from standard usage, and that
is an unfortunate source of confusion.
In the atmospheric sciences, an average (such as an average temperature) is
just what you think it is -- the sum of all the values in a set divided by
the number of values.
A normal is different. It is a the specific average over a standard 30-year
period, currently 1971-2000. For example, a normal temperature is the
average temperature over the 30-year period from 1971 through 2000.

The Midwest becomes the focus today for all the atmospheric ingredients necessary to
produce a major outbreak of severe weather: warm air and moisture streaming into the
region from the Gulf of Mexico, ample sunshine providing additional heating, a cold front
approaching from the west and a powerful jet stream surging overhead. The Storm
Prediction Center places Chicago in a 45-percent risk area today(45 percent chance of
severe weather in any given circle 50 miles in diameter.)

CHICAGO'S HOT WEATHER SEASON

A temperature of 90 degrees is the benchmark definition of a hot day. By that standard,
Chicago's "hot season" extends from April 10 (the date of the city's earliest-occurring
90-degree day) to Oct. 6 (the latest occur- rence. The city logs an annual average of 24
days at or above 90 degrees, and the average first occur- rence is on May 29.

--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
What technology was available to meteorologists that helped them prepare
weather forecasts for the D-Day invasion on June 6, 1944?

Brian O'Carroll, Glenview, Ill.

Dear Brian,
World War II meteorologists did not have the tools that are so important to
today's forecasters -- computer models, satellite information, Doppler radar
data and remote weather observations. They relied instead on available
surface and upper-air observations to draw their weather maps, and they used
meteorological expertise to forecast the movement, development and
dissipation of the weather systems.

WW II forecasters correlated current weather systems with analogous past
situations and often based their forecasts on the outcome of those past
events. Using such techniques, Allied forecasters accurately predicted a short
period of clearing skies that allowed the successful invasion of the
Normandy beaches.

On Wednesday, Lake Michigan demonstrated yet again its ability to alter Chicago's
weather. While temperatures climbed into the 80s in the southern suburbs, lakeside
residents in northern sections donned jackets and sweaters to ward off the fog and
chill of afternoon readings only in the 50s. But that's a fading memory 24 hours later.
Borne in on brisk southerly winds, heat and humidity spread to all sections of the
Chicago area today. Such sharp temperature contrasts, aided by the energy from
strengthening winds aloft, fueled thunderstorms —many of them severe—Wednesday
afternoon and evening. A tornado touched down seven miles south of Flanagan (91
miles south of Chicago) near Pontiac in Livingston County at about 8 p.m. Wednesday
and another occurred near Rensselaer, Ind., at 7:30 p.m. Severe storms were ongoing as
of 9 p.m.

GULF-COAST LEVEL DEW POINTS ARRIVE

Humid air of Gulf origin arrives in the city Thursday in the wake of morning
thunderstorms. Dew-point temperatures, a preferred measure of atmospheric moisture,
become uncomfortable for most people when they surpass 65 degrees. Computer
forecasts indicate the level will be attained this afternoon.

--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Mr. Skilling,
You once ran a piece about the number of daylight hours being the same
everywhere on Earth. Could you please repeat that information?

John Windgrove

Dear John,
The number of daylight hours in a 365-day year is always 4,380 and it
doesn't matter where you might call home. Arctic polar bears experience the
same number of hours of daylight annually as African elephants and Antarctic
penguins. Cloudiness aside, the sun shines for an equal amount of time on
every square inch of the Earth's surface.

The complication is that, because the Earth's axis of rotation is tilted
23.45 degrees from the plane described by its revolution around the sun, the
daily hours of light, planet-wide, are distributed unequally through the
year. At the poles, daylight comes in six-month blocks; at the Equator it is
always within a few minutes of 12 hours a day.

Following a spring characterized by persistently cloudy skies and sub-normal
temperatures, Chicago's weather regime is embarking upon a dramatic change. Warm
—even hot—air that has maintained a multi-day presence across the southern U.S. is
expanding north. In response, Chicago's temperatures climb toward the upper 70s
Wednesday, then jump toward 90 degrees Thursday. The transition will be turbulent,
with a parade of vigorous disturbances across the area in upcoming days, each
accompaned by strong thunderstorms.

CENTRAL ILLINOIS WALLOPED BY HEAVY RAINS TUESDAY

Waves of t-storms roared across central Illinois on Tuesday, bringing additional rain to
an area already drenched from a week of excessive rainfall. Doppler precipitation
estimates indicated localized 8-inch amounts even before Tuesday's onslaught. And
it’s not over yet—periods of thunderstorms continue Wednesday.

--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
While driving across Nebraska in May and watching distant thunderstorms, the
lightning bolts streaking through the sky were immense. Just how long can
lightning bolts be?

Dominik Majerski

Dear Dominik,
The Vaisala Group, headquartered in Vantaa, Finland, has been conducting
extensive lightning studies in the United States. Lightning researcher Ron
Holle of Vaisala says the company has developed a very high resolution
three-dimensional lightning detection system that is in operation in the Dallas-Ft.
Worth area. The network continuously measures the emissions of lightning flashes in
the very high frequency range.

"It has measured quite a few flashes over 100 miles long,” Holle said. “Our current
record length (as of 2006) is 120 miles from a flash. I don't think we would have
expected this, but there they are!"

Monday's 86-degree reading (the city's highest temperature thus far this season and
the warmest in nearly eight months) yields to cooler air today, but heat returns
Thursday -- and persists. Chicago's temperatures have climbed to 80 degrees or higher
on only four days this year (17 days by this time last year), but forecasts on five of the
next seven days contain readings above 80 degrees. Higher humidities, too, will
accompany the arrival of this season's first multi-day stretch of summer warmth. It's
also likely to be a turbulent period. Computer models indicate a powerful 70-90 m.p.h.
jet stream shoots from Missouri into central Illinois today, and that will enhance
thunderstorm development. Other disturbances sweep across the area Thursday and
Friday and again on Monday, and thunderstorms will accompany each of these events.

SEVERE THUNDERSTORM POTENTIAL

Chicago sits within a 30-percent-chance area Tuesday. That means there is a 30
percent chance that a severe storm will occur within 25 miles of any given point.

--By Richard Koeneman, WGN Weather Center Meteorologist

Dear Tom,
On a recent trip to Playa Del Carmen, Mexico, I noticed a perfect rainbow
around the sun when it was almost directly overhead. What was this
phenomenon?
Bob Arnold, Mokena, Ill.

Dear Bob,
What you saw was a solar halo, a fairly common occurrence produced when
sunlight passes through a thin veil of cirrus clouds (clouds that are
composed of ice crystals).
The colors of such halos are often dim, but they can be vivid when the
atmosphere is exceptionally clean. A full spectrum of colors is visible in
those instances, with the colors ranging from red to blue. Most halos form in a
22-degree ring around the sun, and fainter versions, usually whitish, also occur around
the moon.

In weather folklore, halos are said to foretell precipitation because a veil
of cirrus is often the precursor to approaching storms.

Originating in the central Plains, storms will track through the Midwest this week. After
a sunny start to the workweek Monday, warm, moist southerly flow riding over a warm
front to the south will spread showers and thunderstorms into northern Illinois on
Monday night. The storms will continue Tuesday with occasional downpours. By the
time the rain diminishes, totals well in excess of an inch may be widespread over the
Chicago area. Northeast Illinois should experience a brief break in the clouds early
Wednesday, only to have another warm front produce showers and thunderstorms later
in the afternoon and at night.

JULY-LEVEL HEAT LATE THIS WEEK
As the warm front moves well north of the Illinois-Wisconsin line, strong southerly
winds are expected to usher in midsummer-like temperatures and humidity Thursday
and Friday. Depending on cloud cover, some high temperatures -- especially to the
south -- could approach or even touch 90 degrees.
Another band of showers and thunderstorms could hit Friday night into Saturday.
Rainfall totals for the week ahead could easily reach 2 to 3 inches at many locations
across northeast Illinois, southern Wisconsin and northwest Indiana.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
Why does the weather change?
Dorrease Williams
Dear Dorrease,
The unequal application of heat energy to the Earth's atmosphere drives
weather changes, and almost all the energy that fuels the weather comes
ultimately from heat energy contained in sunlight.
Because the Earth is a sphere whose polar axis is approximately
perpendicular to the sun's rays, its equatorial regions receive much more
heat from sunlight than do its polar regions. Therefore, the Earth's
equatorial regions are warm and the polar regions are cold.
It's crucial to the explanation to realize that warm air is less dense,
relative to cold air. Air density differences established by temperature
contrasts drive global wind patterns that attempt to equalize atmospheric
density differences and reduce temperature contrasts. The ongoing interplay
of warm and cool air masses causes what we refer to as "the weather."