May 2008 Archives

Today is the first day of meteorological summer (June-August), and it is expected to
usher in a week of generally above-normal temperatures that will probably extend well
into the following week. A west-to-east jet stream flow aloft over the United States is a
good indicator that colder Canadian air will be held well to the north. Illinois will rest on
the northern flank of warm air centered over the southern United States. Expect brief
clearing intervals between extensive periods of cloudiness and showers and
thunderstorms associated with frequent low pressure systems.

SEVERE STORMS TARGET THE MIDWEST

The National Weather Service Storm Prediction Center has indicated several outbreaks of
severe storms are possible across the Midwest this week. Chicago is included in projected
potential severe storm areas Tuesday and again later Friday.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,

Is it a myth to count the number of seconds between lightning and thunder to find the
distance of the lighting? It was not true between 2 and 3 a.m. Sunday, May 25. Thunder
followed some bolts, but other bolts had no thunder.
--Tom Litke

Dear Tom,
The “lightning rule of five” that you are referring to is this: Count the number of seconds
between flash and crash, and divide by five. That gives the distance, in miles, between you
and the closest portion of the lightning bolt. That rule of thumb is as valid as it always
has been because the physics behind the transfer of sound waves through the atmosphere
has not changed. However, practical application of the rule can be difficult. Be sure to
make a correct link between a given flash and its thunder. Also, thunder rarely carries
beyond 15 miles, but lightning is often visible far beyond that.

Wild weather hammered sections of the Chicago area in stages Friday. The day began
with a seiche along Lake Michigan. Seiches occur when lake levels gyrate rapidly in
short periods of time, and they are produced when fast-moving squall lines push
domes of water into the Michigan shoreline. The waves are reflected back to Chicago
and when this happens, produces the oscillating lake levels. Friday's seiche, which
occurred between 6 and 7 a.m., involved 26-inch variations in just minutes -- changes
amplified in spots by the shape of the shoreline.
Then, powerful winds gushed out of collapsing thunderstorms late morning and
midday. Hardest hit were sections of Lake and McHenry Counties where winds gusted
above 60 m.p.h., snapping trees and power lines and flipping a semi on Interstate
Highway 90 in McHenry County.
The day's third wave of storms bombarded the far southern suburbs near Kankakee with
huge hail the size of tennis balls. The hail fell so prolifically from 57,000-foot-tall
storms, it covered the ground. Torrential rainfall at Milford in Iroquois County -- 60
miles south of Chicago -- generated more than 6 inches in just two hours. A series of
tornado touchdowns Downstate on Friday included one in Springfield.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I am in the third grade, and our class is studying about weather. My teacher
said I should ask you if it ever got to 100 degrees in Chicago.
Zain Mohammed
Dear Zain,
Chicago's temperature has indeed risen to 100 degrees, though not very
often. Chicago weather historian Frank Wachowski reports that the
thermometer at Midway Airport has registered at least one day at or above
100 degrees in 30 of the 80 years (1928-2007) for which we have data at that
location.
And one (but only one) of those super-hot days occurred in May, and right at
this time of the year. On May 31, 1934, the Midway temperature zoomed to
102. Chicago's all-time high temperature was also recorded at Midway
Airport: a scorching 109 degrees on July 23, 1934.
Chicago's most recent 100-degree day occurred three years ago: 104 on July
24, 2005.

Carole Fortenberry e-mails to tell us hail hit Manteno in Kankakee County.
Carole tells us:

"Well, tonight, we had some hail, a ton of it. I have NEVER seen hail SO HUGE.
I hope there wasn't much damage.
I thought I would send you a link to see the hail we had..."

Link to Carole's hail video (opens in a new window)

We would indeed! Thanks for the report and the video, Carole!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Severe storm warnings and tornado watches throughout Illinois make for a busy day in the weather center. Watch Tom's Before the Forecast to find out what this weekend's weather has in store for us.

My colleague Eric Sorenson, chief meteorologist at WREX-TV in Rockford, forwards this
photo taken on that city's east side in the wake of this morning's powerful winds.
Belinda Sullivan was the photographer, and we thank both Belinda and Eric for sharing
this with us.
WeatherBug sensors clocked wind gusts to 56 m.p.h. at northwest suburban Island
Lake, Ill., while gusts of 61 m.p.h. were reported to the National Weather Service at
Gurnee and 58 m.p.h. gusts swept an area 6 miles south/southeast of Beach Park. The
winds were spawned as thunderstorms collapsed while racing across the area.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Belinda Sullivan, Rockford, Illinois

Towering thunderstorms bombarded the Plains and western Midwest on Thursday,
spawning dozens of reports of twisters in Nebraska and Kansas and unleashing
drenching rains and tennis-ball-size hail as far east as Iowa. A powerful new eastbound
spring storm was behind the latest severe weather outbreak. The system threatens the
Chicago area with its own share of weather woes Friday.

Evening Doppler radar scans in the region put the blockbuster storm's cloud tops at
60,000 feet -- nearly twice the cruising altitude of jetliners. Rainfall hit 4 inches
northwest of Des Moines at Jefferson, Iowa, and topped 3 inches at O'Neill, Neb. By late
evening, 10 states from eastern New Mexico to Iowa were under tornado, thunderstorm
and flash-flood watches.

ONLY 2 DAYS LEFT IN COOLEST METEOROLOGICAL SPRING OF LAST 6

With the clock ticking on the March through May meteorological spring season,
Chicago temperatures are more than a degree below normal and more than 4 degrees
cooler than a year ago. It's the coolest spring here in six years.

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

Dear Tom,
Chicago's temperatures jump all over the place, but what daily high
temperature occurs most often? And what about the lows?
Pam Tellock

Dear Janice,
To find the answer, we scanned the entire Midway Airport temperature data
set from Jan. 1, 1929, through Dec. 31, 2007 -- a period of 79 years
made up of 28,854 days. The results might surprise you.
As determined by the Midway data, Chicagoans experience daily high
temperatures in 80s more frequently than any other 10-degree interval, and
nighttime low temperatures most frequently in the 30s.
The most commonly occurring specific high temperature is 80 degrees
(registered on 569 days) followed by 78 degrees (533 days), and the most
frequently occurring low is 32 degrees (634 days) followed by 31 degrees
(602 days).

On today's edition of Before the Forecast, Tom gives us the latest on the warmer weather headed our way and also the severe weather risk for tomorrow. Find out the latest in today's webcast!

Mark Vogan reports temperatures are headed for 70-degrees the next two days in
Scotland and shares theis beautiful sunset shot with us taken Wednesday evening.

Thanks Scott!

-Tom Skilling

Photo courtesy of Mark Vogan, Glasgow, Scotland

High clouds help produce the halo you see here around the sun just before midday
Friday near Griffith, Indiana

Jill Nix of the Marathon Pipe Company in Griffith, Indiana tells us she and and her
co-workers observed this halo around the sun as they left for lunch around 11:35
a.m. today (Thursday). Ice crystals refract or bend incoming sunlight much as a prism
does.

This break sunlight down to its basic colors and is behind the halo formation you see
here. Had today's clouds been composed of raindrops rather than ice crystals, a
"corona" rather than a halo would have been observed. Coronas are also bright
circles but, unlike halos, the bright circle of light that makes up the corona actually
hugs the disc of the sun.

Thanks for the great picture, Jill!

-Tom Skilling

Photo courtesy of Jill Nix

Jim Marocchi was cycling Wednesday evening in Winfield, Illinois, and stopped to
shoot the beautiful evening sunset! Many thanks for sharing your photos with us,
Jim!

-Tom Skilling

Photo courtesy of Jim Marocchi

It's unlikely daytime temperatures are going to flirt again with 50 degrees -- as they
did Tuesday -- anytime soon. Chicago readings rebounded to 62 degrees Wednesday
and are predicted to surge to 73 degrees Thursday and 80 degrees Friday. The big
atmospheric changes behind the warm-up show no sign of abating in the coming two
weeks -- a period in which nearly all daily average temperatures are likely to finish near
or warmer than normal. It's a welcome change which more nearly parallels the warmth
observed here a year ago when the high reach 88 degrees.

The three month "meteorological summer" season begins as June arrives Sunday --
and not a moment too soon. Three of four days this month have been cooler than
normal.

Storm development is accompanying the warm-up to Chicago's west. In New Mexico,
baseball-size hail (2.75 inches in diameter) bombarded Conchas beneath
54,000-foot-tall thunderstorms.

SUNNY WEDNESDAY ARRIVES ON HEELS OF 6 CLOUDIER THAN NORMAL MONTHS

Wednesday hosted 100 percent of its possible sunshine -- only the second time this
month skies have been completely clear. Sunshine has fallen short of historic norms
each of the past six months.

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

Dear Tom,
The recent big temperature drop prompts me to ask what our all-time largest 24-hour
temperature drop might be.

Tim Bonham, Chicago

Dear Tim,
Huge temperature fluctuations are among the defining characteristics of Chicago's
vigorous climate. From Monday into Tuesday area residents experienced a 24-hour
temperature collapse from the low 80s to the low 40s. The city's largest-ever
temperature decline dwarfs that 40-degree tumble, however. At 4 p.m. on Nov. 11,
1911, Chicago's temperature peaked at 74 degrees, a record high for the date. Then,
readings plunged as arctic air surged in. By 12:30 p.m. on the 12th -- 20 1/2 hours
later -- the temperature was 13 degrees.

From one afternoon to the next, Chicago's temperature had crashed 61 degrees, a
tumble that still stands as the city's largest 24-hour temperature change.

Is this cold weather coming to an end for good? Find out what Tom has to say about the this week's possibly warmer weather in this edition of Before the Forecast.

If Tuesday's jarring temperature pullback seemed harsh even by often finicky May
temperature standards, weather records confirm your suspicion. Not only was the day's
50-degree high the coolest to occur this late in a season since measurements at O'Hare
International Airport began nearly half a century ago (since 1959), the 31-degree
plunge between Monday and Tuesday was one for the books too. A one day high
temperature drop of that magnitude has occurred at O'Hare in May only two times
before. The month is a whopping 7.8-degrees behind the same period a year ago and
ranks 35th of the past 138 Mays placing it among the 25 percent coolest on record here
since 1871. Only eight Mays in the last 50 years have been cooler.

DOWNSTATE FARMERS FORCED TO REPLANT IN SWAMPED FIELDS

Unwelcome rain fell in Downstate Illinois on Tuesday where many farmers have
struggled to plant the year's corn crop and face replanting due to flooded fields.
Goreville and Creal Springs -- both near Marion -- recorded 1.97 inches. The region
has seen a foot more rain this spring than a year ago.

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

Dear Tom,
On May 26 on the news the weather report mentioned a "pneumonia front"
coming through the Chicago area. What is a pneumonia front?

Michelle Kramer, Elmhurst, Ill.

Dear Michelle,
It's not a technical meteorological term and it has nothing to do with
pneumonia, but a "pneumonia front" refers to a strong
northeast-to-southwest-moving cold front occurring on the western shore of
Lake Michigan in the spring or summer.

It is accompanied by the sudden onset of gusty northeast winds and a sharp
temperature drop at the lake shore, with readings sometimes plummeting from
the 70s into the 40s in less than an hour. Temperature changes are less
abrupt farther inland.

The term was first used by the Milwaukee Weather Bureau Office in the 1960s
and was probably coined by then Meteorologist-in-Charge Rheinhart Harms (who
is also credited with "panhandle hook" and "Alberta clipper").

Meteorologist Mike Tannura, who interned with us years ago when studying
at Iowa State, shares these spectacular tornado shots from Cedar Falls,
Iowa with us. Mike tells us:

"They were sent by a friend of a friend and I thought you would find
them interesting -- I think this guy is essentially in the non-condensation
area of the tornado! Pretty wild..."

Wild indeed, Mike! MANY THANKS!

-Tom Skilling

Mike Tannura

Photo courtesy: Mike Tannura

Everyone seems to be talking about today's nearly historical temperature drop. Find out what Tom has to say about it in today's webcast of "Before the Forecast."

Storm chaser Kevin Walters watched in horror as this storm descended on
Parkersburg, Iowa late Sunday afternoon. The storm, as much as a mile wide and
categorized in a post storm survey by National Weather Service personnel an EF5 by
National Weather Service, decimated a huge swath of the Iowa community not far
from Waterloo, killing seven during its horrible rampage. Kevin snapped this shot of
the storm and shares this account of his storm encounter with us:

“This is the tornado that hit Parkersburg. It is very had to see because of poor
contrast. The tornado is behind the farm buildings. I saw three separate tornadoes.
At one point I had debris falling from the sky as I drove in driving rain and hail. I
caught glimpses of the wedge as it was wrapped in rain. Storm motions were
amazing, it looked like the entire updraft base was on the ground. I tried to get
ahead of the tornado so I could drop south to get better contrast but downed power
poles caused me to detour twice. I could not catch up after debris covered the road
near Hazelton. This storm too a very similar path as a violent tornado in 2000, both
missed Waterloo by a couple of miles to the north.”

Thanks for sharing this with us, Kevin. Our hearts go out to the residents of
Parkerburg and to family member who lost loved ones.

Tom Skilling

Photo courtesy: Kevin Walters

The photos our storm chasers have sent us of this past week’s tornado-generating
storms have been nothing short of stunning. This latest set from photographer David
Mayhew, taken last Friday in Kansas, are so spectacular, they almost transport us to
the scene just by looking at them. David provides the following backround for each
shot:

“The 2 on Friday were in Dighton Kansas. The 1st shows a funnel spinning up over a
barn. The 2nd shows a condensation funnel that other chasers reported as touching
down.

COD2008Sun034 shows a tornado that touched down briefly (probably 15 secs) from
this high contrast rapidly rotating wall cloud also seen in 049 and 054 at Rush
Center, KS. 067 shows a dustnado spinning up to the rear of the wall cloud. A little
east from Rush Center (about 8 miles east).”

Photos courtesy of David Mayhew Photography, Chicago

Many thanks, David, for sharing these with us! They are incredible!

Tom Skilling

The chill has returned. Gone are Monday's well-timed 80s which, in combination with
generous sunshine and southwest winds, pushed the warmth out past the Lake Michigan
shore, where temperatures hit 83 degrees in Lincoln Park. The sunshine and warmth
provided ideal conditions for Memorial Day barbecuing.
Midway Airport's 84-degree high was the city's warmest thus far in 2008 and only the
third 80-degree-plus high of the year. Over the past half century, just four years have had
fewer 80s by this date. The warmest area highs included 85 degrees at southwest
suburban New Lenox and 84 at both Wheaton and Orland Park.
Sinking air in the center of the continent beneath two merging jet streams is behind the
development of a sprawling high pressure responsible for Tuesday's strong northeast
winds, and is likely to keep cool temperatures in place through midweek.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
In late May 1947, Wisconsin was hit by a snowstorm. What was the weather
like in Chicago?
Bruce Tatge, Janesville, Wis.
Dear Bruce,
It seems incredible, but an unprecedented late-spring snowstorm did strike
portions of the Midwest from northern Iowa to eastern Upper Michigan with as
much as 10 inches of snow on May 28-29, 1947. Hardest-hit Wisconsin areas
were in the southwest portion of the state where 10 inches of snow fell just
south of La Crosse. The weight of the heavy snow caused severe damage to
power and telephone lines and the already-leafed-out vegetation. The
responsible storm center passed south of Chicago, bringing the city a cold
rain and some thunderstorms, highs in the 50s and strong winds. The storm
produced high swells and high waves on Lake Michigan from Kenosha to
Milwaukee, damaging waterfront property. Chicago did set a record low of 38
degrees on May 29, 1947, but that was eclipsed by a 37 degree low in 1984.

Today is just the third day of the year that topped 80 degrees, but there is cooler weather ahead. Find out all of the details in this special Memorial Day edition of Tom Skilling's Before the Forecast.

Storm chaser Chad Cowan was busy Sunday in Kansas where he encountered this
tornado near Hays in the western part of the state. Please check out the video he
relayed to us and which you can view by clicking the link below. Chad provides us the
following rundown of what you will see in the approximately 14 minutes of video:

1) ~0:30 mark, the dramatic double wall cloud structure with one almost
reaching the ground
2) ~5:00, the MASSIVE wall cloud almost on the ground with a small town going by in
the foreground, sirens blasting and then a left turn into the storm puts the whole thing
in view
3) ~9:00, the 3rd supercell takes on a 'mothership' appearance, very ominous and very
close
4) ~11:00, 80 m.p.h.-plus RFD blast almost knocks me off my feet, mesonet crew
scrambles into car

Here's the link (video will open in a new window): http://www.vimeo.com/1067800

Those of you who joined us at the Fermilab this past April had a chance to meet Chad
Cowan. Chad was one of our speakers and is an active storm chaser who was in Kansas
the day of the devastating Greensburg tornado there last May. That EF-5 twister all but
obliterated Greensburg, a community which is involved in a major effort to rebuild in
the wake of that devastating storm. Chad also introduced us to the Storms of 2007
video at the seminar, ALL proceeds of which are being turned over the Red Cross and
Greensburg to aid in the rebuilding process. Thanks Chad for sharing this with us!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of Paul Hadfield

Prolific lightning generated by the thunderstorms which swept across the area
overnight was also photographed by Paul Hadfield. The storms lambasted a corridor
from Texas north to Minnesota, Wisconsin and Michigan, producing the largest
single-day outbreak of severe weather across the U.S. of the 2008 season. Tragically,
the outbreak turned deadly to Chicago's west. It's reported that seven perished in the
Iowa storms and one in Minnesota. The Storm Prediction Center logged an eye-catching
527 severe weather reports Sunday, among them 46 preliminary reports of tornado
touchdowns. Our thanks to Paul Hadfield for these shots!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Mike Frankowski captured this stunning cloud-to-ground stroke in overnight
thunderstorms as they swept the Chicago area. This particular shot was taken by Mike
in the South Elgin area. Top WeatherBug rainfalls included: 1.38" at Sugar Grove, 1.23"
Darien, 1.20" Glenview, 1.17" Glencoe, 1.16" Wilmette, 1.15" Northbrook, 1.09" De Kalb,
0.99" Aurora, 0.95" Naperville, 0.92" Island Lake, 0.91" Oswego, 0.90" Highland Park
and 0.88" South Elgin--just to list a few. Many thanks to Mike for sharing this photo
with us!

Another note: Veteran observer Frank Wachowski reports Chicago's Memorial Day
(Monday) temperature hit 80 degrees just before 1 p.m. at Midway Airport, making
today only the third 80-degree reading of 2008 at the site. Thanks Frank!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Jim Bayne shares this shot of Sunday's Bike the Drive. The weather was
beautiful and we thank Jim for this photo!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

A potent weather system that will be moving through the Chicago area Monday blasted
areas to the west with numerous tornadoes and large hail late Sunday.
Several twisters swarmed northeast Iowa, north and east of Waterloo, damaging homes in
the area. At least one person was killed when a twister leveled at least 50 homes in Hugo,
Minn., just northeast of Minneapolis. Hail as large as baseballs accompanied the tornadic
storms.
The storm system, feeding on warm, humid air sweeping north into the Mississippi Valley,
produced nearly 400 severe weather reports through 9:15 p.m. Sunday, including at least
35 twisters.
SEVERE T-STORM THREAT MONDAY
Tornado watches were posted for northwest Illinois Sunday evening, and the remnants of
these storms will pass through northeast Illinois early this morning. More storms should
develop in today's warmth and humidity and could become severe, especially south and
east of the city.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
How often do we reach 90 degrees or higher on Memorial Day?
Nick Recchia, River Grove
Dear Nick,
With its late-May occurrence, Memorial Day is celebrated before Chicagoas
weather usually turns hot. Prior to 1971 it was observed on May 30 and since
then on the last Monday in May. Since 1871 the official Chicago temperature
has reached the 90-degree mark on Memorial Day in only eight years, most
recently in 2006 when it climbed to 91 degrees on May 29. The high
temperature on the holiday has never been higher than 93 degrees, a reading
recorded twice, first in 1942 and again in 1953. In reality, many Memorial
Days in Chicago are quite chilly, putting a damper on holiday picnics and
outdoor celebrations. The high temperature has failed to reach 60 degrees on
22 Memorial Days including two very chilly holidays (42 degrees in 1889 and
46 degrees in 1894) when the mercury failed to get out of the 40s.

There has been a dearth of 80-degree days in Chicago this year, with only two on the
books as compared to 13 by this time last year. However, all that is about to change as
gusty southerly winds send temperatures soaring into the lower 80s across the
metropolitan area Sunday -- just in time for the Memorial Day holiday.

After a week dominated by chilly northeast winds and sub-60 degree highs, the city is
about to enjoy a warm period well suited for outdoor activities. A storm system slowly
approaching from the Plains will feed the warmth along with increasing humidity,
setting the stage for gusty, possibly severe thunderstorms on Memorial Day, though a
few storms could arrive as early as Sunday evening.

Highs should top out around 80 degrees again on Memorial Day, though readings will
drop in the afternoon after the rain arrives.

BRIEF MIDWEEK COOLDOWN, THEN ANOTHER WARM WEEKEND

Cooler weather will settle in midweek with readings in the 60s as northeast winds
return. However, temperatures will rebound by next weekend as southerly winds bring
another round of temperatures in the 80s and the possibility of showers and
thunderstorms.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,

Dear Tom,
Earlier this month, video clips were shown of Mark Grace's "hit-for-the-cycle" game on
May 9, 1993. The ivy was bare then, but this year on about the same date the ivy was
quite full. Was it a much cooler spring 15 years ago?

Art Schlicht, Sugar Grove

Dear Art,

There may be other factors in play that influence the emergence of the Wrigley Field ivy,
but based solely on temperature, it appears that a cool April may have been the culprit.
April 1993 was quite cool in Chicago with the mercury topping 70 only twice. In
contrast, this April produced eight days of 70 degrees or higher, including a warm
82-degree high on the 25th. It finally did warm up in early May 1993 with seven days
topping the 70 mark including a summerlike high of 87 degrees on May 9, the day
Grace hit for the cycle--and I’m sure the ivy fully emerged by mid or late May.

Gargantuan thunderstorms -- some 66,000 feet tall -- unleashed swarms of tornadoes
on the western Plains for a second consecutive evening Friday. By nightfall, NOAA's
Storm Prediction Center had tallied nearly three dozen reports of touchdowns. At one
point, a large tornado was reported by storm chasers on the ground just 9 miles
southwest of Greensburg, Kan. -- a community demolished by a twister last May.
Northbound hot air -- which sent readings in Texas soaring to 107 degrees at Laredo,
102 at McAllen, and 100 at Midland and Austin -- energized the storm outbreak, and is
to send Midwest temperatures surging Sunday. If thunderstorms remain north and west
of Chicago on Sunday, the year's highest temperature is within reach -- and the warmth
is to extend into Memorial Day, though powerful thunderstorms may erupt in the
afternoon and evening.
MAY'S CHILLY REPUTATION GROWS
Friday marked the 9th time this month Chicago failed to reach 60 degrees. The
57-degree high was the coolest for a May 23 in 21 years and was in stark contrast to
the 89-degree high a year earlier. The month is now about 8 degrees below a year ago.
Only four Mays since 1980 have been cooler.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Is there any meteorological explanation for all the violent weather
occurring around the world -- cyclones, earthquakes, tornadoes, etc.?
Barbara Hampton, Chicago
Dear Barbara,
Worldwide, increases in reported severe weather occurrences result from far
larger populations in weather-vulnerable areas and better communication of
the events rather than a greater frequency of severe weather.
Consider the U.S. Gulf Coast. Prior to the 1950s, it was sparsely populated,
and landfalling hurricanes often struck between population centers.
Also, note that some phenomena (such as volcanoes, earthquakes and tsunamis)
are geological events, not meteorological. Their occurrence is independent
of the atmosphere and the weather. The U.S. Geological Survey says the
frequency of huge earthquakes (magnitude 7.0 or greater) has remained fairly
constant.

Tom Skilling introduces us to the whole Weather Center crew! In this edition of Before the Forecast, you'll meet Cindy from CLTV, Steve from the early Sunday paper Bull Dog, Bill the all-purpose weather producer, Nelson the Tribune weather page artist, and John the intern. Also, find out what the holiday weekend weather will look like and whether we'll be having beach-friendly weather.

Members of the Paul Sirvatka's College of Du Page tornado chase team are sure to be busy again Friday in the Plains. Another day of severe weather is predicted -- and the storms are to continue erupting through the Memorial Day weekend. Joining the College of Du Page chase is photographer David Mayhew, who's shared his remarkable shots of lightning and other weather phenomena with us over the years. David took the amazing photos we share with you here on Thursday (May 22) in the western Plains as severe weather erupted. Hail approaching grapefruit size fell from some of the gargantuan 51,000-foot-tall thunderstorms which swept the area. Preliminary reports filed with NOAA's Storm Prediction Center include four dozen reports of twisters, including the one which ravaged northern Colorado's Windsor, killing one person and injuring dozens. Many thanks to David for relaying these images to us -- they are stunning!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photos courtesy of David Mayhew of Chicago

By Sunday, when south winds bring 80s to the Chicago area, the chilly easterly winds
predicted to produce the month's ninth high below 60 degrees Friday will be a memory.
Only five other Mays over the last half century (since 1958) have produced as many or
more days this cool.
When it comes to early season warm weather, easterly winds are truly the bane of May
here, blowing 50 percent of the time off Lake Michigan's chilly waters. There's been
only one 80-degree high this month back on May 6. Only 11 years since 1928 in the
city have had so few 80s.
Dramatic changes loom here. From early Saturday's isolated mid 30s in the coolest
outlying locations -- temperatures low enough to produce a bit of patchy frost toward
the Fox Valley and areas far west -- warming begins in Saturday's nearly unlimited
sunshine. And by Sunday, powerful south winds and surging humidities should push
temperatures well into the 80s.

PLAINS HIT BY DEADLY SEVERE WEATHER; MORE ON THE WAY THERE
The western Plains were punished by waves of powerhouse thunderstorms responsible
for at least three dozen reports of twisters. At least one turned deadly at Windsor, Colo.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
Has Chicago ever had exactly the same high and low temperatures on
consecutive days, or even three days in a row?
Ed Kozak, Burbank, Ill.
Dear Ed,
Chicago's weather is in flux almost all the time. Occasionally, though, when
weather systems are hardly moving, with a little luck the city can register
identical high and low temperatures on two consecutive days.
A computer scan of 137 years of Chicago temperatures (1871-2007, a period
encompassing 50,038 days) reveals that 287 pairs of days logged identical
highs and lows -- an average of two such occurrences per year; most recently
Aug. 26-27, 2007, with highs/lows of 79/60 degrees.
Three days in a row? Exceedingly rare: only four events; Aug. 11-13, 1879
(82/65); Aug. 26-28, 1882 (74/70); Sept. 5-7, 1910 (81/68); and Nov. 22-24,
1920 (42/37). It has never occurred four days in a row.

It's a dramatic weather day: baseball size hail, supersize thunderstorm and severe weather throughout the western states. Tom also gives some "rock solid" numbers for Memorial Day. Find out all of the details inside Tom Skilling's Before the Forecast.

Chicago's beaches open Friday but cool temperatures riding northeast winds will
hardly have area residents dashing for chilly lake waters. Lake Michigan is 1 degree
cooler than a year ago and at its chilliest levels in four years. But huge changes are
under way that have air masses across North America on the move. Powerful winds--
clocked as high 105 m.p.h. at the 4,900-foot level of Yucca Mountain and 63 m.p.h.
at White Sands, N.M., sent record triple-digit heat in the Southwest packing
Wednesday, whipping visibility-reducing dust into the air. Visibilities near El Paso
dropped to near zero in blowing dust while 50 to 60 m.p.h. gusts at San Simon, Ariz.
made it impossible to see much more than 100 feet.

SUNDAY'S HIGH TEMPERATURES HEADED WELL INTO THE 80s

A sharp temperature rebound, driven by 30 m.p.h. southerly winds and
compressional warming produced as air sinks and compresses beneath the nose
(leading edge) of a powerful jet stream set the stage for a stunning turnaround
Sunday. Readings surge to 85 degrees—the warmest of 2008 and the highest here
since 87 degrees Oct. 8.

Dear Tom,

I am tired of Chicago's temperature extremes and would like to move someplace
where readings remain relatively stable and on the cooler side. Any suggestions?
--John Mannos, Chicago

Dear John,

We don’t want to lose you. But to answer your question, the Pacific Coast of
California and Oregon will come closest to satisfying your desire for a relatively stable
and cool temperature environment. Bathed by moderately cool air that prevailing
westerly winds carry in from the Ocean, the coastal zones of those states rarely
experience extreme temperatures.

Daily normal high/low temperatures on the San Diego coast, for example, range from
61/48 degrees in January to 72/58 in August. Coastal northern California and coastal
Oregon run a few degrees cooler.

On rare occasions, summer heat waves of a few days duration can send temperatures
into the 90s, even along the coast.

In today's installment of Tom Skilling's Before the Forecast, he gives you a sneak peek of the forecast for Memorial Day weekend and shows off his temperature chart.

It's always great hearing from Mark Vogan, who follows our weather blog from Scotland
and is good about keeping in touch with reports on the weather across the Atlantic in
the UK. Mark and his wife Karen traveled 200 miles south to Manchester, England
Tuesday and share these photos they took on the way. Mark tells us:

"We actually went down to'Old Trafford' home of Manchester United Football Club. It
was a long but fantastic day away and the weather, though cool, was beautiful and
sunny. We couldn't have asked for better and wanted to share these pictures with you,
Tom."

Many thanks Mark! It is always great hearing from you!

-Tom Skilling

Photos courtesy of Mark Vogan, Glasgow, Scotland

Our thanks to Alex Janito for sharing this photo of Tuesday's evening's sunset in Oswego, Illinois!

-Tom Skilling

Photo courtesy of Alex Janito, Oswego, Illinois

The International Space Station rises in the southwest then passes overhead Wednesday
night between 9:40 and 9:47 pm

Thanks to e-mailer BobK who alerts us to Wednesday night’s pass of the International
Space Station between 9:40 and 9:47 pm. Here’s additional information Bob has been
kind enough to forward to us:

Weather permitting, the best viewing of the International Space Station flying
overhead in quite a while will be this Wed May 21 at 9:40pm. The space station will fly
directly overhead between 9:40pm and 9:47pm, making it a very long and bright event.
(Of course, it will still be just a very bright moving “star” in the sky).

Here is a map of its path (Note: This is designed to be printed out and held overhead, so
that the compass directions are correct) It will rise in the south-west around 9:40pm,
pass overhead at approximately 9:44pm, and finally set in the north-east around 9:47
p.m.

Temperatures appear headed for the 80s Sunday and Monday—a dramatic turnaround
from May’s stubbornly chilly opening three weeks The month is nearly 2-degrees below
normal and 7 degrees behind the same period a year ago. To date, it ranks among the
eight chilliest Mays here since 1980. Lake Michigan’s average surface temperature, as
estimated by National Oceanic and Atmospheric Administration satellites, has crept 10
degrees higher in the past two months—yet only averages 41 degrees. A predicted
windshift to the northeast later Wednesday night is to tap the cool air which sits above
the lake surface and keep it coming ashore through week’s end. This will limit shoreline
highs to late March levels of low 50s even as inland areas flirt with the low and mid 60s.

Record-breaking heat in the Southwest is to come to an unceremonious end in the
next two days as unseasonably cool air dives into the region. Temperatures are to
plunge 30 degrees.

IT’S BEEN WARMER BY NOW 90% OF TIME

Chicago highest temperature so far this year has been just 82 degrees, back in April; 72
of the past 80 years—90 percent of them—have recorded warmer readings by this date.

Dear Tom,
Which wind direction brings Chicago its highest temperatures in the summer?
Paul Sarewich, Chicago

Dear Paul,

Southwest winds (southwest-to-northeast-blowing winds) bring Chicago its highest
temperatures.

The southern Great Plains--the area from Kansas across Oklahoma into central Texas--
routinely experiences the nation's highest non-desert temperatures in the summer.
Chicago sits to the northeast of that area, and so it takes southwesterly winds to
transport hot air from that region to the city. But Chicago's highest summer
temperatures can occur only when southwest winds overcome the cooling effect of Lake
Michigan. That usually happens when high pressure is centered over the Southeastern
U.S. and a stationary or slowly-moving cold front stretches from the Dakotas to Lake
Superior.

Tom's trying out a new web-exclusive segment that we're calling Tom Skilling's Before the Forecast. Here, he'll tell you what's happening behind-the-scenes in the WGN Weather Center as he and his team prepare the forecasts every day.

Monday marked the second day temperatures failed to escape the 50s at Midway
Airport--something that has only happened this late in the season an average of one
year in five at the Southwest Side site since 1928. O'Hare's 60-degree high was a
little better. The month's opening 19 days ranks among the coolest 40 percent on
record with 13 of them posting deficits. The remainder of the work week is to remain
unseasonably cool as northwest winds keep resupplying the area with bursts of chilly
air off a stubborn pool of cool air draped across much of eastern Canada. A blocking
pattern in the arctic has locked that air mass in place for more than a month. But
potentially well-timed changes loom over the upcoming Memorial Day holiday
weekend. Eastbound warm air could push temperatures close to this year's highest
level to date by Memorial Day.

BLISTERING HEAT ON THE MOVE OUT WEST; DEATH VALLEY SIZZLES AT 120 DEGREES, PHOENIX AT 110 DEGREES

Even by Southwest desert standards, Monday's searing heat was one for the books.
Death Valley, Calif., sizzled at 120 degrees while residents of Phoenix were treated to
the year's first high of 110 degrees. Las Vegas wasn't far behind with a peak reading
of 108 degrees.

Dear Tom,
While sailing on Lake Michigan, the sun is both overhead and reflecting off the water
on a sunny day. Does the addition of the reflecting sun change the exposure time for
getting a sunburn on water versus on land?

Gerald Migely, Chicago

Dear Gerald,
"The higher incidence of skin cancers in sailors and farmers was one of the first
clinical clues that ultraviolet (UV) radiation is a carcinogen." Said Dr. Bryan Schultz, an
Oak dermatologist. "Most of the risk for sailors is in the long exposure times, but the
percent of UV reflected is also a factor."

Water reflects only about five percent of light when the sun is high, but the shiny
surface of a boat may approach 80 percent. "This does increase one's UV dose
significantly," Schultz said. UV reflection increases as the sun drops below 45º, but
those rays, filtered through more atmosphere, are much weaker.

Our friend David Lindgren, who farms in De Kalb County and regularly reports to us
on the weather and crop conditions out that way, reports welcome drier weather most
of this past weekend finally allowed our northern Illinois farmers to get into their
fields and plant a lot of corn and soybeans. David was among them Friday and
Saturday then took time out for a drive on Sunday during which he took the beautiful
shots we share with you here. He and his wife Colleen were in northwest Illinois and
northeast Iowa in Mississippi River country. Their trip took them from the southern
branch of the Chicago Galena Stage Coach Trail onto Route 30 to the Mississippi
River into Iowa. David and Colleen spotted the White Pelicans pictured above and a
spectacular panoramic shot from the Mississippi Palisades State Park. Thanks David
and Collen!

Tom Skilling

Picture courtesy of David Lindgren of De Kalb County, Illinois

My friend, colleague and longtime Alaska resident Tom MacPhail, now working with
the National Weather Service in the Washington, D.C. area, returned to the Great Land
for a conference this past week and was good enough to send us these panoramic
views taken this past weekend of snow covered Mt. Alyeska in Girdwood. The
mountain is located 40 miles southeast of Anchorage. Tom reports spring in south-
central Alaska has been a cool one, much like here in Chicago, and that the
emergence of spring vegetation, which will take place with increasing speed in the
weeks ahead, is running behind. Little wonder Mt. Alyeska is still so stunningly snow
covered! The top of the mountain was buried under nearly 900” of snow this season.
Thanks for the wonderful photos, Tom!

Tom Skilling

Photos courtesy of Tom MacPhail in Girdwood, Alaska

Professional photographer David Mayhew, who’s always stunning photos have graced
the pages of this blog many time over the years, has sent us this photo taken over
the weekend of a halo around the sun. David is currently out in the field with Paul
Sirvatka’s College of DuPage storm chase team and hopes in the coming week to
photograph any storm activity the group encounters. Keep us posted, Daivd, and
thanks for another stunning photograph!

Tom Skilling


Photo courtesy of DavidMayhewPhotography, Chicago

With upper-air jet stream winds stuck in a northwest flow, cooler Canadian-source
high pressure will be the dominant factor in Chicago's weather in the days ahead. Rain
may be plentiful Downstate, but Chicago and the northern third of Illinois should miss
most of the action. Light showers are expected Monday night and Tuesday, and a band
of rain is likely to skim by mainly to the south of the Chicago area later Thursday. By
Saturday, southerly winds should usher in a warming trend and an increasing chance of
significant rains that could persist well into the first part of next week.
AS WEST COAST HEAT MOVES INTO PLAINS, SEVERE WEATHER THREATENS
Sunday was the fourth consecutive day of record highs in California. An excessive heat
watch was posted for Southern California, southern Nevada and western Arizona, where
100-degree highs were commonplace. Phoenix recorded its first 100-degree high of
2008 on Sunday. This West Coast heat is expected to end by Tuesday as an upper-level
low-pressure circulation moves into the Southwest. Subsequently, warm moist
southerly flow directly out of the Gulf of Mexico will set the stage for heavy rains and
severe weather in the Plains later this week.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
I have observed high-altitude jets dispensing heavy, non-dissipating trails behind them,
unusual in that they expand across the entire sky, turning a once-blue sky into a
complete cover of milky white. Tom, these are not condensation trails.
--Jeff Blondell
Dear Jeff,
Ah, but they are. Water vapor is one of the gaseous products of combustion and, when
added to the air in the exhaust of jet engines, condenses into visible clouds of ice
crystals--the wispy, cirruslike clouds that we see as condensation trails (contrails)
behind high-flying jets. Temperatures and humidity at flight altitude determine whether
contrails form and how long they last. In dry air, contrails will not form, or they will be
small and evaporate in a few seconds. In moist air, they persist for hours, often
"seeding" their own further growth.

With strong low pressure to the northeast of Lake Huron and cold high pressure
sinking south out of Canada into Minnesota, north to northwest flow brings
unseasonably cool air into northern Illinois today. Very cold air aloft makes the air
mass unstable, with only a small amount of solar heating possibly triggering widely
scattered brief showers this afternoon. The most unstable conditions that produced
some 31 severe weather reports in Minnesota, Wisconsin and Michigan Saturday is
positioned farther north and east today.

BLOCKING PATTERN ALOFT CHANGES LATER THIS WEEK

The strong high pressure ridge that has brought record warmth to the west coast —
dozens of record highs were set from California to Washington Saturday—and the
large low pressure trough that has guided a cool northerly flow aloft over the Great
Lakes and Midwest will modify as it slowly drifts east in the coming days. By Thursday
a strong low pressure center is forecast to develop over the Southwest and the upper
Great Lakes low will be centered over the northeast U.S. This should bring significant
cooling to the west coast and allow a warm-up in Chicago by the end of the
workweek.

Dear Tom,

What might be the relationship between clouds and fog? Is low-lying fog actually a
cloud?

—Leon J. Hoffman, Chicago

Dear Leon,
Physically, clouds and fog are identical. Both are visible aggregates of water droplets
(or ice crystals) so small that they are nearly suspended in the air. Clouds differ from
fog only in that, by definition, fog is either at the ground or within several feet of it,
whereas the bases of clouds are aloft. It’s a convenient shorthand to say that cloud
and fog droplets are “suspended” in the air, but that is technically incorrect:
Thedroplets do fall. The fall rate is so slow—generally only 1 foot per minute, or less
—that, for all practical purposes, clouds and fog appear to be suspended. A final
distinction: Meteorologists also consider a visible concentration of smoke or dust
aloft to be a cloud.

Spectacular weather including a second consecutive 70-degree day greet Chicagoans Saturday. Critical steering winds aloft, responsible for guiding weather systems, are blowing from the northwest. This sends cooler air into the area above ground, a development that should make the area increasingly vulnerable to cloud formation, especially in the warmer hours of the day, and most noticeably Sunday. Several of the puffy cumulus clouds expected to decorate Saturday skies may build tall enough to generate a few spotty showers in the afternoon. But cooling aloft fosters even more cloud development Sunday and shower coverage may be more extensive. Temperatures topped out at 107 degrees Friday in Anaheim and Modesto, Calif. The northwest flow ensures the record-breaking triple-digit heat that grips much of the West Coast won't head this way anytime soon. But big changes loom in the current pattern that has lingered for more than a month, delivering cool temperatures and frequent rain. The new pattern signals warmer, more humid air next week and 2008's warmest temperatures to date.
RAINFALL FORECASTS NOT ENCOURAGING
A return to heavier rainfall is predicted over the next two weeks. As much as 2 to 4 inches may be on the way.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
My son, age 7, has become deathly fearful of thunderstorms. Short of professional help, can you offer any suggestions?
James Smith, Madison, Wis.
Dear James,
The high winds, beating rain, lightning and crashing thunder of violent storms prove humbling to all of us, but they can be especially frightening to children. Here are a few tips that will allow you to confront and ease children's storm fears: Communicate with them—don't deny their fears. Let them know it is normal to feel afraid and explain that the storm will end. Remain calm and cool. Children take behavioral cues from parents and react accordingly. Shelter family pets during a storm so children will know they are safe. Assure children that lost or damaged toys, articles of clothing, etc., can be replaced; explain that it is more important that the family is safe.

A dome of incredibly hot early season air scalded California on Thursday. The heat,
which produced readings 25 to 30 degrees above normal at many locations, smashed
records from California to Oregon. Perennially mild Seattle is predicted to turn
downright steamy Friday with highs surging into record territory, topping out near 90
degrees. It's looking increasingly likely the air mass could bring Chicago and the
nation’s Heartland it's first surge of summer-level warmth later next week.
Temperatures Thursday soared to a record-breaking 99 degrees at Oakland and
Sacramento, 103 degrees at Redding and 104 degrees at Red Bluff. The heat,
expected to blaze into the weekend there, will send the risk of wildfires soaring.
In Chicago, lakeshore residents shivered in Thursday's east winds. Temperatures at
the University of Chicago only reached 49 degrees and O’Hare's 57 degrees was 13
degrees below normal and far below the 80 degrees on the date a year ago.

MORE HEAVY RAIN DOWNSTATE

Downstate farmers, anxious to get into their fields and far behind in planting this
year's crops, were dealt another blow by heavy rain Thursday which reached 1.75
inches at Christopher—just northeast of Carbondale.

Dear Tom,

Years ago, I remember hearing seiche (pronounced saysh) warnings mentioned for
Chicago's lakefront. Could you please explain that phenomenon?

Royse Cramton, Oak Park, Ill.

Dear Royse,

In the Great Lakes Region, any sudden rise in the water level in a harbor or on the
shore of one of the Great Lakes is known as a seiche. In extreme cases, the rise,
occurring within a minute or less, can be several feet. Such dramatic events obviously
present great danger to people at the lakeshore.

The Chicago seiche situation is unique. In rare cases, an air-pressure jump in
advance of southeastward-moving thunderstorms can push a low surge of water
from Chicago across Lake Michigan. Upon striking the Michigan/Indiana shore, the
surge reflects back to, and focuses upon, Chicago's lakeshore,initiating a sudden,
temporary rise in the lake level.

Californians are being warned to monitor the elderly and conserve electricity in the
coming days as temperatures soar to 100 degrees. Sections of the San Francisco area
are likely to reach or exceed 90 degrees while the state’s inland valleys bear the
brunt of the heat with sizzling highs up to 105 degrees. Desert-like relative
humidities threaten to support wildfires.

The heat isn't limited to California. Readings 20 degrees above normal may set new
records from Los Angeles north to Seattle. In Portland, Ore.—where mid 60s are
typical this time of year—unusual 90s are predicted each of the next two days.
Mid May arrives in Chicago with the month's temperatures running within a half
degree of normal—but a noteworthy 6.5 degrees cooler than a year ago. The month's
3.09 inches of rain is twice normal and nearly as much as a full May’s rainfall (3.38
inches). A year-to-year comparison is even more dramatic. Rainfall in the opening 15
days this month is 24 times the 0.13 inches recorded by this date a year ago.

ONLY TWO 80s HERE SO FAR—UNUSUAL COMPARED TO THE PAST 80 YEARS

With no 80s expected here until the week after next, the two 80s on the books stand
out. Only 14 of the past 80 years (since 1928) have recorded so few 80s by mid-May.

Dear Tom,
Why do we name hurricanes and typhoons but not tornadoes?
Stan, 11 and Ted, 9, Jatczak, La Grange Park

Dear Stan and Ted,
Tropical cyclones are named to enable better communication between meteorologists
and the public. Frequently multiple storms are active and naming the storms reduces
confusion and helps the public keep the storms straight.

In 1950, previously anonymous Atlantic Basin tropical cyclones were named using the
phonetic alphabet (Able, Baker, Charlie, etc.). From 1953 until 1978 only women’s
names were used, but starting in 1979 lists of alternating women’s and men’s names
were developed, a system still in use today.

It also makes sense to name tropical cyclones because they can roam the oceans for
days or weeks, while most tornadoes last for just a few minutes.

However, significant tornadoes or major tornado outbreaks are named after the fact,
like the Oak Lawn tornado or the Palm Sunday tornadoes.

A big THANK YOU to those of you who took the time to e-mail us shots of Tuesday
evening's gusty showers and thunderstorms--and the rainbows which followed. Low
angle sunlight interacting with these storms provides a great environment for rainbows
and we've been treated to more than our fair share in recent weeks. Please check out
these photos from folks all over the Chicago metro area! We love receiving your
weather photos! Many thanks to all who took the time to send them along!

-Tom Skilling

Photos courtesy of Taylor Spooner, Aurora, Illinois

Francis and Paula Regelbrugge of west suburban Sugar Grove share this shot of Tuesday
evening’s rainbow there. Thanks Francis and Paula!

Photo coutesy of Francis and Paula Regelbrugge, Sugar Grove, Illinois

Regina Janito sends us this shot taken by her eight year old son Alex in Oswego, Illinois. Thanks Regina and Alex! A great shot!

Photo courtesy of Regina and Alex Janito, Oswego, Illinois

Hanover Park residents were treated to this rainbow in the wake of Tuesday evening’s thunderstorms. Robin Biggs photographed it and shares it with us. Thanks Robin!!

Photo courtesy of Robin Biggs, Hanover Park, Illinois

Mike Toohill of Bloomington, who keeps us well informed on downstate crop
development during the growing season, shares this photo of the small hail which hit
the Bloomington area late Tuesday. Hail wasn’t limited to the Bloomington area. Nickel
to quarter sized hail was reported in a number of Tuesday evening’s thunderstorms
across northwest and north central which towered to 43,000 ft. high at times and
produced more than cloud to ground lightning strokes within approximately a 200
miles radius of Chicago in the 10 minute period 6 and 8 p.m. The storms unleashed
wind 50+ m.p.h. wind gusts at Carpenterville, Hoffman Estates and South Elgin as they
swept through between 6 and 8 pm Tuesday evening.

-Tom Skilling

Photos courtesy of Mike Toohill, Bloomington, Illinois

Temperatures returned to the 70s Tuesday for the first time in a week. Readings of
74 degrees at Rockford, Wheeling and Chicago's Midway Airport topped the day's
high temperature list. It marked the 14th time in 2008 that the mercury has topped
70 degrees and set the stage for late afternoon thunderstorm development. By
evening, nickel- and quarter-size hail had been reported from the Mississippi River
east to Dixon. Hailstones 1 inch in diameter showered down on Ogle County's
Oregon around 5:25 p.m., prompting a severe thunderstorm warning. By that time,
lightning was flashing earthward from the base of 43,000-foot-tall cumulonimbus
clouds (thunderheads) within a 200 mile radius of Chicago at nearly 400 times a
minute.

Powerful winds gushed out of the leading edge of the eastbound storms, reaching 52
m.p.h. at suburban Long Grove, Mundelein and Carpentersville early Tuesday
evening.

ONLY FOUR MAYS IN THE LAST HALF CENTURY WERE WETTER HERE

May's rainfall at O'Hare International Airport reached 2.99 inches prior to Tuesday's
storms, making it the 17th wettest opening for the month here since 1871. Only four
Mays in the past half century have opened wetter.

Dear Tom,

I'm old fashioned and I like to hang my wash outside to dry, but I only do this during
the summer. Would clothes still dry even in colder winter temperatures? Would it be
worth trying?
-Marlene Forst

Dear Marlene,

A sunny day is conducive to hanging your wash out anytime, but you will be
disappointed during the colder months.

Drying (evaporation) rates are a function of the air's ability to hold moisture, and this
is determined by temperature. Cold air has a very small capacity to hold moisture,
and a full day on the line on a cold day might still result in damp or frozen clothes.

Sunshine itself has a minor effect, raising the temperature of the clothes and adjacent
air molecules a few degrees.

Indirectly, though, sunny skies usually indicate a dry air mass and, hence, increased
evaporation.

Monday’s chill in Chicago was an annoyance to those waiting for a sign that spring’s
warmth was close to taking over. But it beat the wind-driven rains that lambasted the
country’s Mid-Atlantic —from North Carolina to New York City. Wind gusts reached
near hurricane force along Maryland’s coast, gusting to 69 m.p.h. at Ocean City. At
nearby Washington, D.C., 3.82 inches of rain fell, marking the city’s second deluge this
month. It pushed May’s precipitation tally to 7.69 inches—five and a half times normal.
A rainfall of 7 inches was recorded at North Beach, Md.

Chicago’s 56-degree high tied May’s coolest reading—but the lakeshore area bore the
brunt of the chill. Highs reached just 44 degrees in Highland Park and in Wrigleyville,
and 46 degrees at Wilmette and Glencoe.

TUESDAY’S HIGH TEMPERATURE IN CHICAGO REBOUNDS TO THE 70s

Highs surge 18 degrees Tuesday to 74 degrees—a reading likely to be the warmest of
the coming seven days. The overall pattern continues to be cool over the next two weeks.

Dear Tom,
Are tornado warnings ever issued for funnel clouds?
-Patricia Nesbit

Dear Patricia,
A meteorologist would not hesitate to issue a tornado warning based on a
funnel cloud if the report appeared to be reliable and could be associated with a
Doppler radar that shows a rotation in the clouds in the area.
A funnel cloud becomes a tornado when it hits the ground. During periods of severe
weather, it could only be a matter of seconds before a funnel reaches the ground and
starts causing damage.

Storm spotters and weather professionals often use the redundant phrase “tornado on
the ground” to convey a sense of urgency and danger to the public about an
approaching twister. The redundancy makes it clear that the storm is an actual tornado
and poses an immediate threat.

It was nasty Sunday in Chicago as heavy rainfall lashed the city, blown about by
northeast winds gusting to nearly 50 m.p.h. The greatest rain totals occurred from
the city westward, with Midway Airport recording 1.93 inches and Aurora measuring
2.05 inches. The rain let up by early afternoon, but strong northeast winds kept an
unseasonable chill in the air throughout the day. The sky is expected to clear
Monday, and with the return of sunshine, temperatures should climb into the lower
60s inland—though lake-chilled winds will keep shore areas in the 50s. It should be
even warmer Tuesday as south winds send the mercury into the lower 70s for the
first time in nearly a week.

A STEAMY MOTHER'S DAY IN FLORIDA

In contrast to Chicago's rainy chill, record heat gripped the Sunshine State. Record
highs were established in many areas, ranging from 93 at Pensacola to 96 at Miami
and Ft. Lauderdale.

TWISTERS STRIKE EASTERN CAROLINAS

Severe weather continued Sunday evening with tornado damage and injuries reported
in eastern North Carolina near Elizabeth City and Morehead City and in South Carolina
near Charleston.

--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
What is the date of Chicago's latest freeze?
--Shirley Bell
Dear Shirley,
Chicago's latest freeze occurred 16 years ago when the mercury fell to 32 degrees at
O'Hare International Airport on May 25, 1992. The previous morning was also chilly with
a frosty low of 34 degrees, and back-to-back minimums of 33 followed May 27-28.
Just six years ago, the city experienced its second-latest freeze when the thermometer
registered 31 degrees May 21, 2002. These freezes stand out because they are a full
week later than the previous latest freeze set May 14, 1895, with a low of 32. The two
latest freezes were established at O'Hare's more rural environment, which fosters
somewhat lower minimum temperatures than the city's earlier official thermometer
sites, which were near the lake until 1942 and then at Midway Airport through 1979.

Chilly, wind-driven rain is expected to pummel the Chicago area Sunday, forcing
Mother’s Day celebrations indoors.

More than an inch of rain is likely to fall in many locations in heavy downpours before
the rains diminish to light showers in the afternoon. High temperatures will struggle
to reach the lower 50s, and as strong northeast winds gust in excess of 40 m.p.h. in
the afternoon, readings should drop back into the 40s, making 2008 the coolest
Mother’s Day here since a 50-degree high back on May 12, 2002.

DEADLY TORNADOES SWARM SOUTHWEST MISSOURI

Numerous tornadoes struck southwest Missouri late Saturday. Early reports indicate
three were killed, with many injured and extensive damage. Towns hit included
Neosho, Newtonia and Seneca.

Dear Tom,
What is the difference between a hurricane, a cyclone and a typhoon?
—Jessica Vega

Dear Jessica,

There is no difference. Unfortunately, meteorological jargon and popular usage
variously apply different or overlapping meanings to those three words. In
meteorological parlance, a cyclone is a lowpressure system. Hurricanes and typhoons,
too, are low-pressure systems, but they are a specific kind of cyclone—tropical
cyclones (logically, cyclones that form in the world’s tropical and subtropical zones).
Hurricanes (in the Atlantic Ocean), typhoons (western Pacific Ocean) and cyclones
(Indian Ocean and Australia) are different names for the same type of storm. In
popular usage in the United States, “cyclone” is applied loosely to tornadoes,
waterspouts, dust storms, hurricanes and even to any strong wind.

Saturday's sunny open isn't to last. Clouds marking the approach of a windy Mother's Day
storm expected to soak the area Sunday arrive as the day proceeds, but not before
Chicago temperatures reach the 60s away from the lakeshore. However, cooling east
winds are expected to restrict shoreline highs to the 50s.
LATE SHOWING OF BACK-TO-BACK 50s
The chill that has gripped the area since Thursday is more than a bit unusual by historic
standards. The 59- and 58-degree highs here Thursday and Friday are the first
back-to-back 50s to occur on a May 8 and 9 here in a quarter century. In addition, 80
years of weather records dating back to 1928 at Midway Airport indicate that fewer than a
third of mid-May highs fail to crack the 60-degree mark.
IT WAS WARM THIS TIME A YEAR AGO
By contrast, Chicago was in the midst of early-season warmth at this time last year.
Saturday's predicted 63 degrees falls 21 degrees short of the 84-degree high a year ago.
Interestingly, last year's first 90-degree day was to occur in only a week's time on May 14.
May 2007 ended up with 13 days of 80 degrees or higher.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
A lot of Chicago's moisture comes from the saltwater Gulf of Mexico, so why isn't our
rain salty?
Bob Johnson, Oak Park
Dear Bob,
Since the beginning of time, the saltwater oceans have been the reservoir of about 97
percent of this planet's water supply. The water is constantly being recycled,
evaporating into the atmosphere and returning to Earth as rain or snow in an ongoing
hydrologic cycle. Sea water is indeed salty, with about 35,000 parts of salt per million
parts of water. However, the salt in sea water is only dissolved in it and not chemically
bonded, so it is left behind when the water evaporates, like when a pot of saltwater is
boiled dry on a stove. That is the reason sea air is salty when the ocean's spray
evaporates, and also why precipitation falls as fresh water. When salty ocean water
surges inland as in a hurricane storm surge, it can kill vegetation.

Runaway Runoff

Pavement, buildings and other waterproof surfaces cover a large portion of the land in urban areas like metropolitan Chicago. That means rain water cannot soak into the ground. Instead, it gushes into storm drains that discharge directly to local rivers and streams.

About 55 percent of rainwater that falls on a city runs off (and in intensely urbanized locations such as the Loop, runoff approaches 100 percent); only 15 percent of rainfall sinks in to recharge groundwater supplies. The remaining 30 percent evaporates back into the atmosphere.

For comparison, only 10 percent of rain that falls on natural ground cover (forests, wetlands or other natural areas) runs off, and about 50 percent soaks into the ground.

As rainwater runs over city surfaces, it picks up pollutants encountered along the way -- soil, oil and grease from cars, pesticides and fertilizers, pet waste and much more. Not only do such pollutants harm fish and wildlife, they also degrade drinking water supplies and often require that recreational waterways be closed.

What can you do?
If you plan to replace a walkway, driveway or patio in your yard this spring, consider using water-permeable surfaces such as wood decks, spaced bricks or concrete lattice instead of solid concrete or asphalt. These surfaces allow water to soak through to the ground, thereby reducing runoff from your property and helping to replenish groundwater supplies.

Temperatures on Chicago's North Shore failed to break out of the 40s Thursday. Such
readings are more typical of late March than May. Wilmette topped out at just 48
degrees while Highland Park struggled to 49 degrees and Glencoe only made it to 50
degrees. Chicago's official 59-degree high at O'Hare International Airport was 8
degrees below normal and a far cry from an 82-degree high only a year earlier. It
marked the chilliest May 8 high here since the 51-degree high for the date 24 years
ago in 1984.

The cool weather continues Friday beneath increasing clouds and ahead of an
approaching disturbance that could spark a shower in spots late Friday.

LATEST SOAKER HITS DOWNSTATE

Unwelcome rains drenched the southern Midwest on Thursday. As much as 1.59
inches fell at Freeburg while 1.54 inches was measured at Flora—both east of St.
Louis in Downstate Illinois. The same storm spawned half a dozen twisters across
Tennessee, Alabama and Mississippi. Meantime, still another storm entering the
western Plains produced 68,000-foot-tall thunderstorms responsible for 70 m.p.h.
gusts at Lewis in southwest Kansas.

Dear Tom,

The Myanmar cyclone disaster is horrific. What could account for such a catastrophe?
Steve Bartik

Dear Steve,
The disaster in Myanmar, formerly known as Burma, is staggering. The official death
toll, now at more the 20,000, could climb to 100,000 as a worst-case possibility, said
Shari Villarosa, the U.S. chargé d’affaires in Yangon.

On the evening of May 2, Cyclone Nargis moved from west to east along Myanmar's
southern coast. It brought sustained winds of 125 m.p.h. and a 12-foot storm surge
that swept across the flat, low-lying and densely populated delta of the Irrawaddy
River.

The river branches into several large channels that drain south into the Indian Ocean.
Unfortunately, the north/south orientation of those channels allowed the cyclone's
onshore winds to push storm surge many miles inland.

Two separate waves of heavy rain drenched the Chicago area Wednesday—the latter
embedded within an eye-catching, southbound shelf cloud. The ominous roll-
shaped, wind-tossed bank of clouds developed as winds shifted northeast tapping
chilly air to the north and sending temperatures into a 20-degree dive in less than
three hours. This month’s opening seven days had produced 2.04 inches of rain even
before Wednesday’s downpours arrived—the 11th wettest May opening of the last
138 years.

Area rain totals by day’s end were impressive and included: 1.34 inches in Wilmette,
1.17 inches in Palatine, 1.08 inches at Chicago’s Whitney Young High School and 1.05
inches at Mt. Prospect. In the city, 0.76 of an inch fell O’Hare International Airport
and 0.57 of an inch at Midway Airport. The “normal” full May rainfall tally is 3.38
inches.

SECOND STORM TARGETS AREAS
DOWNSTATE WITH A THURSDAY DELUGE
An unusually active pattern is taking shape—one likely to send a series of storms
across the Midwest over the coming two weeks. A powerful system, responsible for
Thursday’s gusty, cool northeast winds in Chicago wallops areas downstate with
downpours.

Dear Tom,
Please define the "growing season." When does it start and end?
Gregg Dubin, Huntley, Ill.

Dear Gregg,

No single definition of "growing season" is satisfactory for all situations.

Generally speaking, the growing season is the period of the year during which air
temperatures remain continuously high enough for the growth of cultivated plants.

A commonly accepted standard is the number of days between the average dates of
the last spring and first fall occurrences of a temperature of 32 degrees. By that
measure, the growing season varies from 191 days (April 17 to Oct. 24) along
Chicago's lakefront to 162 days (May 1 to Oct. 9) in outlying suburban locations.

Ideally, the growing season should be defined biologically rather than
meteorologically because plant species vary greatly in their tolerance to cold
temperatures.

Our friend Tracey Surface captured Wednesday’s evening’s stunning frontal passage.
The gush of cooler air riding strong northeast winds behind the front produced this
eye-catching “shelf” cloud—a rolling bank of clouds which formed as crashing
temperatures sent readings plunging to the dew point—the temperature of
condensation.

Radar scans put cloud tops as high 25,000 to 30,000 ft—yet amazingly, our lightning
detection system indicated NO lightning. However, 0.75” of an inch fell in under a
half an hour according to our colleague Steve Kahn in Arlington Heights and
motorists were forced to the side of the road because of the downpours which hit
Carpentersville.  Thanks Tracey for another set of spectacular shots.

Photo courtesy: Tracey Surface

May, already wetter than normal—1.28 inches versus 0.67 of an inch—delivers its
latest thundery soaking in waves Wednesday. Warm, more humid air arrives as south
winds increased overnight and 35+ m.p.h. gusts keep the moisture needed to fuel
some potentially energetic downpours coming. While rainfall totals of a half inch or
more will be widespread, locations visited by the heaviest showers and
thunderstorms could get an inch or more.

The system behind Chicago’s Wednesday storms walloped the Plains and western
Midwest with thunderstorms late Tuesday believed to have produced three tornado
touchdowns in Winona County in southeast Minnesota —west of LaCrosse, Wis. In
Texas, 4.5-inch diameter hail (softball size) pummeled Olton while 4.25-inch
diameter hail knocked out windows near Grand Falls. Upon arriving home, a fire
official in Rose, Neb., witnessed a barrage of tennis-ball size hail that covered the
ground to a depth of 8 to 10 inches.

A 30-DEGREE TWO-DAY TEMPERATURE DIVE AHEAD—THE EQUIVALENT OF A LATE
JUNE TO LATE MARCH TEMP SHIFT
Unseasonably chilly air follows the rains. A blocking pattern aloft in Canada means
Thursday’s near 30-degree temp pullback won’t be the last in the next two weeks.

Dear Tom,
Weather-knowledgeable friends say large hail always comes before a tornado, but I
wonder about that. Is it true?
Peter Micham, southwest suburbs of Chicago
Dear Peter,
It is not true. Only the wind fields within and in the area several miles around a severe
thunderstorm provide reliable clues as to the storm's tornado-producing capabilities.
Unfortunately, those telltale signs are rarely apparent to an observer. Only Doppler
radars can detect them.

Severe storms forecaster Roger Edwards of the National Weather Service's Storm
Prediction Center in Norman, Okla., says: "Does hail always come before a tornado?
Rain? Lightning? Utter silence? High winds? Not necessarily for any of those. Hail can
indicate the presence of an unusually dangerous thunderstorm, but it is not a reliable
predictor of tornado threat."

Temperatures surge to within striking distance of 80 degrees the next two days—
potentially the warmest readings here since the 82-degree high on April 25. An 80-
degree high Tuesday would make it the second warmest day of 2008. Crisscrossing
winds through the atmosphere—southwest at ground level and west/northwest only
two miles aloft—combined with faster than normal temperature declines with height
signal the possibility of several thunderstorms erupting this afternoon, especially in
northern sections of the area and out over the lake. The cool winds flowing out of
these isolated storms could surge ashore late today and set up a situation where
storms would build south near the lake—but that’s not yet a certainty. What appears
more likely is the eruption of more numerous storms with the arrival of more humid
air overnight.

DESPITE PREDICTED TEMPERATURE CRASH, 72% OF MAYS THAT START OUT WARM
WIND UP ABOVE NORMAL

The temperatures in May’s first week can offer clues on how the remainder of the
month may fare. When the month’s opening seven days average at least a degree
above normal, May has finished above normal 72 percent of time.

ATW GRAPHIC HEADER LINK:

Dear Tom,

I've noticed that sounds carry better at night than during the day. Could you provide
an explanation?

Louise, Park Forest

Dear Louise,

Sounds do carry better and farther at night. Because it tends to be quieter then,
individual sounds are easier to distinguish. By far the most important factor, however,
is a difference in the temperature structure of the lower few hundred feet of the
atmosphere between day and night.

Sound travels through cold, dense air more slowly than through warmer, less dense
air. When air temperatures change on the path along which sound waves are
traveling, the waves always bend toward the colder air.

By day, it's warmer near the ground and colder above; sound bends up and away from
the ground (and you). At night, it's colder near the ground and warmer above; sound
waves bend down.

Rebuilding efforts continue a year the devastating EF5 twister (indicating winds greater
than 200 mph) which roared at 9:45 p.m. last May 4 (2007) out of the darkness of the
southwest Kansas night leveling Greensburg, Kansas. This photo, taken in the wake of
the storm, drives home the destructive power of that twister. It was the first “5”
classification twister on the Fujita scale to rake any part of the United States since the
devastating Moore, Oklahoma of May, 1999. Evan Ammeson forwarded this photo to
us—it was taken by National Weather Service-Dodge City, Kansas Warning Coordination
Meteorologist (WCM) Jeff Hutton. Evan notes the fire hydrant visible near the center of
this photo which was clearly ripped out of the ground by the force of that frightful
twister and is laying amid all the debris and the leafless trees left in the wake of that
storm.

Check out our webcast of this year’s Fermilab seminar available here on the
WGN-TV website for the fascinating presentation on this horrifying storm presented by
Larry Ruthie of the NWS-Dodge City office who joined us at the early April seminars.
Also, check out storm chaser Chad Cowin’s presentation and the segment her shared
with our Fermilab audience from the stunning Storms of 2007 tape put together by a
group of this country’s best known storm chasers. All proceeds from the sale of that
incredibly well produced tape have been and continue to be donated to the city of
Greensburg and to the Red Cross there to help in the rebuilding of the tornado ravaged
community. Our thanks to Evan Ammeson for calling Jeff Hutton’s photo to our
attention!

Tom Skilling
WGN-TV Chief Meteorologist

Tom Gausselin shares these spectacular double rainbow shots taken Friday night as
powerful storms exited the area. Tom snapped these at Silver Lake Golf Club in Orland
Park. These are amazing. Thanks Tom!

-Tom Skilling

Photos courtesy of Tom Gausselin, Orland Parkvalle

Between Friday night’s storms, Shana Goetz photographed this stunning double rainbow
in southwest suburban Mokena, Illinois. Thanks for sharing this with us Shana—a
stunning shot!

Photo courtesy of Shana, Goetz, Mokena, Illinois

--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
On a visit to the Black Hills of South Dakota, my family and I noticed outdoor neon signs
had screens over them for protection from hail. Is hail that frequent there?
--James Walker, Madison, Wis.
Dear James,
It is. Large hail is massively damaging. It flattens crops, shatters windows, dents cars and
kills birds and small mammals. Chicago experiences an average of two days per year with
hail. Most of it is small and causes no damage. But the frequency of hail, and especially
the frequency of large, damaging hail, increases steadily westward from Chicago. Hail is a
costly problem in the Great Plains, especially across Wyoming and Colorado. Cheyenne,
Wyo., with nine hail days annually, is the "hail capital" of the nation. The Black Hills, 200
miles northeast of Cheyenne, logs six hail days per year.

Saturday's weather in Chicago was more reminiscent of late March, with gusty northwest winds, cloudy skies, scattered showers and high temperatures barely making it into the 50s. Sunday marks the start of a rapid turnaround with sunny skies, southwest winds and temperatures some 10 to 15 degrees higher. Warming peaks in the mid-70s Tuesday. Showers and thunderstorms, featuring downpours and heavy rains, precede the arrival of a cold front later Tuesday night. This storm system signals a change in the upper air pattern featuring a strong west-to-east jet stream flow directly overhead.

STORMS TRACK THROUGH THE MIDWEST
The rain-free period forecast from Sunday into Tuesday may be the longest seen in northeast Illinois for some time. Beginning Wednesday, low pressure systems will move frequently out of the central Plains through the Midwest and Ohio Valley. Computer models indicate that for the next couple weeks in Chicago, periods of cloudiness and showers will linger longer than the infrequent intervals of clearing skies. Starting Wednesday, a cool easterly air flow off Lake Michigan will probably persist well into the weekend. Rains should hit Thursday and then again over the weekend.

Dear Tom,
What U.S. city has the most sunny days in a calendar year?
—Paul Pincawis, Elgin.

Dear Paul,
Few weather and sky phenomena lift our spirits more than a bright, sunny day,
especially after a cold, cloudy and snowy winter such as the one we have just put
behind us. Unfortunately, sunny days are often at a premium in Chicago and across
the Great Lakes region, and the area’s residents will not be surprised to learn that
they dwell in one of the nation’s cloudier areas; only New England and the Pacific
Northwest are cloudier. On average, Chicago logs 84 sunny days per year, well ahead
of cloudy cities like Seattle or Burlington, Vt., (58 days at both cities), but trailing far
behind cities in the nation’s desert Southwest. Yuma, Ariz., heads the list with 242
sunny days per year, followed by Phoenix (211) and Las Vegas (210).

Oak Lawn’s Chuck Hagen photographed this rainbow Friday evening near I-57 in Peotone. Great shot Chuck!


Photo courtesy of Chuck Hagen, Oak Lawn

Our friend Anson Mount shares a spectacular shot with us—this
one of this rainbow visible from Algonquin around 6:55 pm Friday
evening.

Thanks Anson!

-Tom Skilling

Photo courtesy of Anson Mount, Algonquin, Illinois

Many of you were good enough to send us photos of the rainbows which resulted as
Friday evening’s setting sun interacted with rain falling from departing
thunderstorms. Tracey Surface shares this shot with us taken from her condo and
looking out at Montrose Harbor. Thanks Tracey!

-Tom Skilling

Photos courtesy of Tracey Surface, Chicago

Many of you were good enough to send us photos of the rainbows which resulted as
Friday evening’s setting sun interacted with rain falling from departing
thunderstorms. Tracey Surface shares this shot with us taken from her condo and
looking out at Montrose Harbor. Thanks Tracey!

-Tom Skilling

Photos courtesy of Tracey Surface, Chicago

Gusty thunderstorms raked the Chicago area in waves Friday, peppering some
locations with pea-size hail while unleashing downpours so heavy in other
areas that motorists were forced to the side of the road. The 1.28 inches measured
at O'Hare Airporat broke the record of 1.26 inches set in 1979 and included 0.43
inches that fell in just 7 minutes.
An evening cloudburst that hit west suburban Elgin just before 7 p.m. swamped the
city with 1.50 inches in only 15 minutes. Other heavy rain totals included
1.32 inches in Glenview, 1.20 inches in Lombard and 1.14 inches in Northbrook.
Powerful south winds topped 40 m.p.h. in and out of Friday's thunderstorms, and
evening storm gusts were estimated at 50 m.p.h. in sections of Rockford while
WeatherBug wind sensors clocked gusts of 59 m.p.h. at Marshall High School in
Chicago and 56 m.p.h. gusts at Lansing Municipal Airport in southern Cook
County. Storm winds toppled a 2-foot diameter tree in Kankakee.

RAINBOWS CLOSE A STORMY DAY
Friday's stormy weather closed with rainbows visible in many areas as the
setting sun interacted with thunderstorm rains.
--Tom Skilling, WGN-TV Chief Meteorologist

Dear Tom,
I love hot weather. When does Chicago usually record its first 90-degree day? When
was our last 100-degree day?
--Don Grelecki
Dear Don,
Chicago climate records peg the average date of the city’s first 90-degree day
around May 29 based on 80 years of data from Midway Airport. The earliest 90-
degree day ever recorded here occurred back-to- back on April 10-11, 1930.
In 1875, there were no 90s at all, the only year the city failed to reach that
benchmark, according to other records.
Last year Chicago recorded its first 90-degree day on May 14 and in 2006
it occurred on May 28.
Days with highs in the 100s here are not as common. Our last 100-degree
day was July 24, 2005, when the thermometer officially peaked at 102
degrees. Recent highs in the 100s occurred in 1999 and in 1995, when a deadly
heat wave caused more than 750 fatalities.

An immense spring storm 2,200 miles across—easily the season’s biggest to date—is
driving the weather literally from one corner of the U.S. to another. The potent
system threatens a second Friday with severe weather in the Chicago area—including
rotating supercell thunderstorms and possible tornadoes if warming isn’t terribly
inhibited by regular thundery downpours.

A 100-degree north/south U.S. temperatures differential is driving the latest
atmospheric behemoth, which by nightfall Thursday had unleashed crippling snows
on sections of the Plains and Rockies—areas in the 80s only days earlier--while
promoting explosive thunderstorm growth in the Plains. Among the 10 twisters
reported across the Plains by nightfall was a multiple vortex twister—one in which
mini-tornadoes rotate within a larger funnel similar to the one which devastated
Plainfield in August, 1990. That tornado was one of two on the ground
simultaneously near Ralston, Oklahoma. The storms sprung to life as incredibly dry
air featuring desert-like single digit dewpoints, roared at 50 m.p.h. out of the Texas
Panhandle into humid air over the Sooner State.

Dear Tom,
A friend in Iraq has told me that, besides a lot of heat and dust, they had a lightning
storm—no rain, no thunder—just lightning. How can you have lightning and no
thunder?

Mary Abuja, San Diego

Dear Mary,

Thunder is always a by-product of lightning, but sometimes we are too far away to
hear it.

A lightning spark can heat the air through which it passes to 54,000 degrees
practically instantaneously. Such extreme heating causes air to expand explosively,
followed immediately by cooling and rapid contraction. That physical process sets up
sound waves that blast outward, and we hear them as thunder.

However, thunder dampens quickly as it spreads and it rarely carries more than 15
miles from its source, whereas lightning bolts are often visible at distances beyond
50 miles if intervening clouds are not present.