April 2008 Archives

The surging temperatures and gusty winds that mark the start of May on Thursday
bring two days of lake-cooling to a precipitous end. An accompanying moisture
increase, which will give the air a decidedly more spring-like feel, primes the
atmosphere for several showers and thunderstorms Thursday and a potentially more
important outbreak of storms and possible severe weather later Friday. Computer
wind trajectories indicate Thursday’s predicted 70s were over Tennessee, Mississippi
and the Gulf Coast near New Orleans only 24 hours ago.
May is the city’s third fastest warming month, with “normal” highs jumping from 64
degrees to 75 degrees.
Wednesday’s 31 degrees was the second sub-freezing low at O’Hare. Back to back
readings below 32 degrees have occurred this late in the season here in only three
other years in the past half century.

FROM 82 DEGREES TO A BIG SNOW—IN ONLY THREE DAYS!
Western South Dakota is bracing for near blizzard conditions. It was only Tuesday
that Rapid City topped out at 82 degrees. Up to 8 inches of wind-driven snow is
predicted there Thursday/Friday—and up to a foot in the Black Hills.

Dear Tom,
When can I be assured the danger of frost and freezing
temperatures in Chicago is past for good?
Jeffrey Rayner, Chicago

Dear Jeffrey,

Light frost can form on plant leaves on a clear, calm night even when air
temperatures a few feet above the ground are as high as 38 degrees. A heavy, killing
frost usually requires a temperature of 32 or lower.

Because overnight temperatures on any given chilly spring night can, in
extreme cases, vary by 20 degrees across the Chicago area, it is difficult to pin down
an exact date. It really depends on your location.

Here are some guidelines: Near the lake, light frost (38 degrees) has never occurred
beyond May 31; heavy frost (32) never beyond May 14. Within about 2-6 miles inland,
the corresponding dates are June 4 and May 13; 7-15 miles inland, June 22 and May
29; farther inland, add seven days.

Stormy weather continues to sweep Scotland. Mark Vogan has sent us new
photographs of thunderstorms scattered across the beautiful Scottish countryside. He
tells us, “I took these shots this afternoon from our local hills overlooking our valley,
note the low-hanging dark clouds with black scud clouds which raced underneath the
slower moving main cloud base with a distinct rain shaft in the distance. Also note
the large collection of water on roadways.”

Thanks Mark for the excellent update and for the chance to see more of your
beautiful country! Stay dry!

-Tom Skilling

Photos courtesy of Mark Vogan, Glasgow, Scotland

Tuesday’s frigid early March-level 44-degree high temperature fell just 5 degrees
short of the city’s coldest April 29 high—a 39-degree reading set in 1893. It marked
a breathtaking pullback from an 82-degree high just a year earlier and marked the
second day of mid-40-degree highs, something which has happened at Midway
Airport this late in the season only seven times since observations began at the site in
1928. The day opened with a 31-degree low at O’Hare International Airport, tying a
half-century-old record for the coldest April 29 temperature. Suburban lows reached
28 degrees at Aurora and Lincolnshire and 29 degrees at Lombard, Highland Park and
Du Page Airport.
Fifteen states from Indiana to Georgia were under advisories late Tuesday for frost
or freeze conditions overnight.

THINGS LOOKING UP HERE, PLAINS TEMPERATURES SURGING
As Midwesterners shivered, temperatures were soaring in the Plains. Rapid City, S.D.,
and Billings, Mont., topped out at 82 degrees.

Dear Mr. Skilling,

How can a rainstorm or snowstorm travel thousands of miles, constantly depositing
moisture but never running out of it? Why does it not eventually lose steam and dry
up?
John H. Deppen, Portage, Mich.

Dear John,

Your questions rank high among the issues that weather forecasters contend with on
a daily basis. The precipitation-producing capability of a storm system changes
constantly—increasing, decreasing, sometimes ceasing.

The reasons are complex, but one factor stands out: Low-level winds, especially
southerly winds in advance of a low pressure system, constantly deliver "new air" to a
storm system as it moves along. If the moisture content of that new air varies, as it
usually does depending on its source region (like the Gulf of Mexico), the
precipitation capability of the storm system will also vary.

Our friend Mark Vogan, who is our weather eye in the sky in Scotland and keeps us
posted on weather developments there and across the UK, e-mails us these pictures
which offer a clear indication that spring is finally dawning across our hemisphere.
Mark sends us these shots of cumulonimbus clouds developing as he drove home
from work yesterday. He follows up with some pictures of full blown thunderstorms
which cut power at some locations. These aren’t typical, Mark tells us.

“This is a typically dissapointing atmospheric set-up here throughout much of
summer as our Scottish climate does not receive the adequate daytime heating to
really build cumulus clouds into mature cumulonimbus towers. Thunderstorms do
occur during warmer spells but as temps generally average between 60 to 75 degrees
in summer and very rarely rise to greater than 80 degrees (thanks to our small island
geography and cool surrounding waters) all results in a fairly settled summer
atmosphere with few thunderstorms.”

Thanks for updating us and for a set of interesting photos, Mark!

-Tom Skilling

Photos courtesy of Mark Vogan, Glasgow, Scotland

Our thanks to Connie Koehler for sharing these beautiful photos of Monday’s
snowfall on the Koehler farm located between Wisconsin Rapid and Neenah in central
Wisconsin. Parts of Wisconsin received as much as 5” of snow Monday from the same
system which produced wet snow in many parts of the Chicago area. Many thanks
again, Connie!

-Tom Skilling

Photos courtesy of Connie Koehler of Waupaca, Wisconsin

Fewer than a third (31%) of the years on record here since 1884-85 have produced
snow so late in the season. Monday’s snowfall featured especially large flakes—not
uncommon when temperatures are above freezing allowing falling snowflakes to stick
together. It was the second latest occurrence of snow here in the past 15 years.
Temperatures dropped sharply with altitude creating the sort of unstable atmosphere
which encourages air to rise with vigor and clouds to develop vertically, much as a
thunderstorm does. It was not surprising several flashes of lightning occurred in
parts of the metro area despite a daytime temperature of just 38 degrees —a level
more typical of late February and 25 degrees below the normal late April highs. While
snow dusted outdoor objects here, Stevens Point in central Wisconsin received 5
inches.

VIRGINIA TWISTERS INJURE HUNDREDS

The same system responsible for Chicago’s thunderstorms Friday walloped the East
Coast, spawning 10 twisters. Three of the twisters injured at least 200 in southern
Virginia.

Dear Tom,
Why are severe thunderstorm warnings are never issued for lightning?
Jim Froemke, Chicago

The National Weather Service issues a severe thunderstorm warning when it believes
a storm will produce winds of at least 58 m.p.h. and/or hail at least three-quarters
inch in diameter or larger. Lightning ground strikes are not severe thunderstorm
criteria.

Meteorologist Rusty Kapela at the Milwaukee NWS says, "Any convective cloud that
manages to generate one lightning bolt is, by definition, a thunderstorm. If lightning
were a criterion, even a weak thunderstorm such as a garden-variety thundershower
would require the issuance of a warning."

That would greatly diminish the effectiveness of the warnings. Kapela advises that
any thunderstorm should be considered severe with respect to lightning.

Tracey Surface captures the gray, damp spirit of Monday’s weather in Chicago
through shot of Montrose Harbor from her high-rise window. Thanks Tracy!

-Tom Skilling

Photo courtesy of Tracy Surface, Chicago

Friday evening’s (April 25) powerful thunderstorms produced these Sear Tower
lightning strikes photographed by Gaurav Garg of Wilmette. Gaurav asks how the
antenna withstands this and all lightning. The fact is, Gaurav, the antenna is not
being hit directly—the appearance notwithstanding. Instead, a corona of charged ions
which pools up around the antenna is interacting with a charge descending from
above to give off the light we see in these lightning strikes. Thanks for such terrific
shots!

-Tom Skilling

Photos courtesy of Gaurav Garg, Wilmette, Illinois

SEE THE VIDEO!

Melting snow and recent precipitation in Wisconsin has produced these ominously
high waters on the Chippewa Flowage. Daniel Hanson shares these photos with us
and reports he took them just two miles from his home in far upstate Winter,
Wisconsin. Thanks Daniel!

-Tom Skilling

Photos courtesy of Daniel Hanson of Winter, Wisconsin

Huge snowflakes—some the size of half a fist—have fallen over sections of the
Chicago area Monday. Pam Long in De Kalb County these terrific shots of today’s
snow with us. Thanks Pam! It’s the second latest snow to affect the Chicago area in
the past ten years! Not since 2005 have we seen snowflakes here this late in the
season.

-Tom Skilling

Photos courtesy of Pam Long, De Kalb County

Temperatures Monday afternoon will be down nearly 40 degrees from Friday's spectacular
82-degree high as a late-season chill grips the area. Monday’s high temperature is
expected to peak at a chilly 43 degrees, a level typical of early March and is just a few
degrees above the date's record low maximum of 39 established 134 years ago in 1874.
Showers should dampen the day, and with temperatures well below freezing moving in at
cloud level, snowflakes should mix in with the rain. Anxious gardeners buoyed by last
week’s warmth should be aware that the expected low temperatures Monday night and
Tuesday night will endanger newly planted vegetation. Warmer conditions will return by
midweek as the chill subsides.
SOUTHERN CALIFORNIA WILDFIRES FEED ON HOT, DRY CONDITIONS
Wildfires burned hundreds of acres Sunday in portions of Southern California as
temperatures soared and humidities dropped. Afternoon temperatures reached a
record-tying 102 degrees at Fullerton, 103 at Santa Ana and 100 at Woodland Hills with
the humidity at a desert-level 5 percent. Los Angeles International Airport peaked at a
record high of 95.
--By Steve Kahn, WGN Weather Center Meteorologist

Dear Tom,
How rare is it for Chicago to receive snow in May?
—Gladys Reynolds
Dear Gladys,
Snow during May in Chicago is not as rare as you might think. The city’s May snow
records date to 1885, and in those 123 Mays, snow has been recorded in 31 of them, a
frequency of once every four years. Of course, the vast majority of those May snows
were insignificant. But over the years the city has experienced a few noteworthy May
snows. In 1940 the city was surprised by a 2.2-inch snowfall on May 1-2 with some
northwest suburbs receiving as much as 5 inches. On May 3, 1907, 1.3 inches of snow
was logged. The city’s latest measurable May snow took place on May 11, 1966, when
0.2 inches fell. Chicago’s most recent encounter with snow in May took place three
years ago, when a trace was reported on May 2, 2005.

Despite the fact that Chicago's high temperatures topped 70 degrees for six
consecutive days last week, capped by Friday's wind-blown 82-degree warmth, the
city is facing an onslaught of chilly weather in the week ahead that is likely to feature
both snow and frost. The cool weather began its Midwest invasion on Saturday's
gusty west winds and will strengthen its grip Sunday and Monday.
Showers are expected to develop Sunday afternoon. As temperatures continue to
decline, the rain could mix with or change to wet snow Sunday night and Monday.
Recent warmth should prevent the snow from accumulating on pavement, but cold
surfaces and grassy areas may be in line for a late season coating of white. Should
measurable snow(0.1 inches or more) occur, it would mark the city's latest
measurable snow in nearly two decades, when half an inch fell May 6, 1989.

WINTER STILL PACKING A WALLOP
A massive snowstorm hit portions of Minnesota and the Dakotas on Friday night and
Saturday. Up to 19 inches of snow fell near Watertown in northeast South Dakota,
while 16 inches buried nearby Brandon, Minn. Record snowfall also fell near
Anchorage, Alaska, with 17.2 inches down since Friday.

Dear Tom,
There is a family story that says my grandmother melted snow to give my aunt her
first bath. She was born Downstate in Flora, Ill., about halfway between St. Louis and
Vincennes, Ind.., on June 12, 1936. Could this be true?
Nancy Miller, Dyer, Ind.
Dear Nancy,
We are certain it did not snow in Flora, Ill., during June 1936, but we think we
may have found the basis of your family’s story. June 1936 was a hot month in
southern Illinois, with high temperatures reaching the 90s and low 100s on many
days, though on the date of your aunt’s birth the high was only 81 degrees. Flora was
hit by several thunderstorms that month, including some that produced hail and
damaging winds. One of these storms occurred on June 22, battering the area with
hail and 0.8 inches of rain. It is possible your grandmother collected and melted the
hail to give her 10-day-old daughter a bath.

Friday delivered long-awaited 80-degree warmth to the Chicago area. Powerful south
winds extinguished lake cooling and gusted above 40 m.p.h. outside thunderstorms that
swept in waves. The mercury reached the day’s high of 82 degrees at 1:48 p.m. at O’Hare
International Airport—a reading 20 degrees above normal and the first time in 186 days
that temperatures topped 80 degrees or warmer. But that heating, in combination with the
most humid air of 2008, fueled thunderstorms. Dew points in the low and mid-60s
assured plenty of atmospheric moisture for storms that towered to 51,000 feet and sent
lightning bolts within a 200-mile radius of Chicago, charging earthward at just under
2,400 strokes every 10 minutes about 6 p.m. The storms raced across the area at
incredible speeds—moving at 60 m.p.h. much of the afternoon and evening while
bombarding some northwest and west suburbs with hailstones the size of golf balls.
Hardest hit were the Rockford area and Livingston County southwest of Chicago.
Naperville and Aurora reported hail nearly 1 inch in diameter. Storm gusts at Von Steuben
Metro Science Center in the city clocked 66 m.p.h. winds about 7:30 p.m.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
I remember a very warm late April in Chicago when I was a boy in the early 1960s. Can
you tell me what year that was?
Robert Klein
Dear Robert,
We believe the period you remember occurred during late April 1962. After two warm
days in the lower 70s in March, April opened on a cool note, with the high temperature
reaching only the lower 40s on April 1 and 2. The month remained cool for the first
three weeks. Warm weather finally moved into the area April 20, when the mercury
soared to 80 degrees and remained entrenched for the rest of the month. The
temperature climbed to a summerlike 86 degrees April 25, followed by highs of 88 and
86 the next two days as persistent southwest winds pumped very warm air into the city.
After a two-day cool-down to around 70, readings surged back to a steamy 88 degrees
on the last day of the month.

Chuck Hagen shares this remarkable shot of Friday night's lightning with us. He photographed the storm over one of the refineries in Lemont. Thanks Chuck for a terrific shot!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Chuck Hagen, Oak Lawn, Illinois

Daniel Dombrowski shares this view of a towering cumulonimbus he photographed at an altitude of 35,000 feet while flying from Las Vegas to Midway on Wednesday. It's a terrific shot. Thanks Daniel!
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Photo courtesy of Daniel E. Dombrowski, Valparaiso, Indiana

It’s been so quiet since early January in terms of severe weather, the Chicago area has
slipped into the heart of its annual tornado season with little notice. But make no
mistake, we’ve entered a time of year in which the weather can swing from tranquil to
violent quickly. Weather records prove this. Of a total of 309 twisters logged by NOAA’s
National Climatic Data Center over the 16-county region which includes and surrounds
Chicago since 1950, 73 of them—nearly a quarter of this area’s tornado touchdowns
since 1950—have spun up in April. A June tally of 75 twisters makes it the only month
more active.

WEATHER WATCHES WITH LATE DAY STORM OUTBREAK?
Some active northeast-bound thunder- storms over parts of the area early today could
be followed by a more important thunderstorm outbreak this evening and early tonight.
The hours of sunlight warmth between the two clusters of storms and a surge in
atmospheric moisture in the day’s powerful, south to southwest wind gusts to 35-40
m.p.h. at times, set the stage for a late day severe weather outbreak that may
necessitate tornado or thunderstorm watches in the area.

Dear Tom,
What is the difference between a "small tornado" and a "microburst"?
Paul Dunn, Bloomington, Ill.
Dear Paul,
A microburst is an area of strong and often damaging winds that occurs when rain-
chilled air, cooler and therefore heavier than its warmer surroundings,
surges down through a thunderstorm, then "splashes" violently outward when
it encounters the ground. By definition, a microburst affects an area less
than 2.5 miles in diameter.

Microburst winds, though limited in extent, can be strong. On June 29, 1990,
a microburst in Streamwood generated 150 m.p.h. winds that killed a person.

A tornado is a violently rotating column of air than extends from the base of a
thunderstorm down to the ground. The air within a tornado spirals upward in a
corkscrew fashion at speeds typically 100 to 300 m.p.h.

The year's warmest air yet is to send temperatures surging toward 80 degrees in all
but immediate lakeshore areas Thursday—and across most of the Chicago metro area
ahead of thunderstorms Friday. It’s a warm surge expected to send daytime readings
15 to 20 degrees above normal. Not even Wednesday's easterly winds off Lake
Michigan’s numbingly cold low 50-degree waters managed to thwart 70-degree
readings in all but shoreline locations. Midway's 73-degree high marked the seventh
reading of 2008 to top 70 degrees: O’Hare’s 74-degree maximum was its sixth.
The extreme dryness of Wednesday’s air no doubt contributed to the strong warming,
because dry air warms more quickly than moist air. At mid-afternoon, O'Hare's
relative humidity sank to an astoundingly low 17 percent—the driest in an April here
in a quarter-century!

HAIL AND TWISTERS WALLOP PLAINS
Powerhouse thunderstorms pounded seven states Wednesday. More than 200 reports
of severe weather—80 percent of them involving hail—had been filed by nightfall. Ten
tornado touchdowns were recorded. Hail up to 4.5” in diameter (softball size)
pounded Lamesa, Texas.

Dear Tom,
My job requires me to fly often. I have noticed that the "takeoff time"—the time
elapsed between when takeoff power is first applied and when the jet finally lifts off
—is greater during hot, humid weather. What is the explanation?
William Frederick

Dear William,
Air density is the issue. The wings of an aircraft generate lift that is

proportional to the density of the air through which the craft is flying, as well as its
forward speed. Reduce one and you must increase the other in order to compensate.

When attempting a takeoff in less-dense air, the pilot must bring the craft to a
greater speed to attain lift sufficient to get the craft airborne. This takes more time
on the runway.

Weather conditions that reduce air density are precisely the factors that you have
noticed: heat and humidity. Hot air is less dense than cold air and, although it seems
counter-intuitive, humid air is less dense than dry air.

Only a week ago, Chicago’s first official 70-degree temperature of the year arrived
three weeks late. In a dramatic temperature turnaround, including four subsequent
70-degree days—including Tuesday’s 74-degree high—it appears the year’s first 80-
degree day may be only two days away. If all goes as predicted, an 80-degree high
could be on the books here by Friday’s close. Weather history here reveals that
shouldn’t come as a major surprise. An 80-degree day has already occurred by this
date the last seven years. Eighty years of weather observations at Midway Airport
indicate the city typically records its first 80-degree reading on or about April 23.

With just a week to run, April—which started off incredibly chilly—has turned the
corner. A succession of mild temperatures over the last seven days (April 16-22),
which averaged 58.6 degrees, ranks 12th warmest of the last 138 years. The mild
spell has pushed April 2008’s average temperature 6 degrees warmer than a
comparable period a year ago.

HUGE HAIL HITS SOUTHERN PLAINS
Of Tuesday’s 100 reports of severe weather, 90 involved large hail. Golf ball-size
hailstones broke windows and dented cars in Billings in southwest Missouri.

Dear Tom,

Why was the moon shining blood red on the night of Sunday night?

Ken Boncela, Naperville, Ill

Dear Ken,

Many readers commented on the haunting shades of red and orange that the moon
displayed Sunday evening.

The moon does not generate any color of its own, but only reflects sunlight. Lunar
colors on Earth are a measure of our atmospheric clarity as moonlight passes through
it. Like sunlight, the atmosphere scatters the shorter wavelengths of moonlight,
leaving shades of red, orange and yellow. These colors are pronounced when the
moon is near the horizon and its light has to penetrate a greater distance of the
atmosphere. As the moon rises higher, the red/orange hues fade.

Because cloud-free, moonlit nights are often a result of high pressure, colors are
enhanced by haze or dust trapped under a high pressure’s inversion. On rare
occasions, warm colors are replaced by blue tints, a result of smoke from distant
forest fires.

Chilly east winds off Lake Michigan, which deprive shoreline residents the 70s enjoyed
by inland neighbors half the time in a typical April, were at it again Monday. While
O'Hare and Midway reached well into the 70s, temperatures struggled just to make it to
-- if not edge a bit above -- 60 degrees along Lake Shore Drive north to Highland Park
(60 degrees) and Waukegan (64 degrees). It's the sort of temperature spread that
Tuesday's stronger, more southerly winds are likely to whittle away.

The Chicago area, still playing catch-up with 70-degree temperatures, chalks up the
fifth of 2008 Tuesday -- a tally behind the long-term average of eight 70s by April 22.
The 70-degree tally at Midway Airport has been higher by this point in the season 53 of
the past 80 years (or 66 percent of them).

BRUTAL CHILL SMASHES RECORDS OUT WEST, PRODUCES RARE SUBZERO LOWS
Montanans and others across the Northwest have to be checking their calendars. The
chill of recent days has felt anything like spring.

Though readings will begin improving slowly in coming days, Monday morning's low at
Great Falls, Mont., slipped to -8 degrees, obliterating the old 1951 record of 11 by an
astounding 19 degrees.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
What is the earliest date that Chicago has ever reached 90 degrees?
—Wayne Griffin
Dear Wayne,
Chicago’s earliest hot weather occurred nearly 80 years ago, with highs of 90 degrees
on April 10-11, 1930. Just two days earlier, with high pressure over the area, the
mercury dipped to 34 degrees. As the high moved east, strengthening southwest winds
delivered a flood of warm air. The mercury jumped to 70 on April 9, then soared to the
two record early-season 90s. Since 1871, the city has reached the 90-degree hot
weather benchmark only four times in April. The other two occurrences were a high of
90 degrees on April 30, 1942, and a 91 on April 22, 1980. The 1980 high of 91 was
notable because just a week earlier, the city was hit with nearly 4 inches of snow on
April 14-15, a testament to the huge temperature fluctuations Chicago can experience
in the spring.

Everything has to work just right, but if winds flow more south than east, this could end
up being Chicago's warmest day of the year so far. The previous 2008 high of 75 degrees
was recorded at the official O’Hare Airport site just last Friday. Southeast winds off cool
(45-50 degree) Lake Michigan will keep readings along the lakefront in the 60s, but a
more southerly trajectory inland under sunny skies should allow readings to warm into
the mid 70s. On Tuesday, warm and moist southerly flow in advance of an approaching
cold front will result in widespread showers and thunderstorm development during the
day. While a little short on wind strength both at the surface and the jet-stream level
Tuesday, the trajectory of flow is such that strong storms could develop.

COLDER AIR BY NEXT WEEKEND
Temperatures are expected to hit 70 degrees again Thursday, ahead of a low-pressure
system that should bring significant rains Friday. As the low-pressure system and
associated cold front moves east Friday night, strong northwesterly flow should bring a
surge of cold Canadian air over northern Illinois Saturday and Sunday.
--By Paul Dailey, WGN Weather Center Meteorologist

Dear Tom,
Chicago’s temperatures are sometimes higher at night than during the day. How often
does this reversal of the normal temperature cycle occur?
—Thomas Rhiner
Dear Thomas,
Daily high and low temperatures are defined as the maximum and minimum that occur
during the 24-hour calendar day, local standard time. During the winter, Chicago’s
daily high occurs between 1 and 4 p.m. on 40 percent of the days. In the summer, the
percentage rises to 65 percent. On 13 percent of the days (one day in eight) the high
occurs about midnight. Frequently in winter, during a warm-up after a cold spell,
temperatures will continuously rise, with the day’s high being reached at midnight. Or
if a strong cold front passes the previous night, the day’s high will come at midnight at
the beginning of the calendar day, with temperatures falling the rest of the day.

High temperatures approach at least 70 degrees today and then reach into the middle
70s Monday and Tuesday as it looks more and more like spring 2008 has indeed
shifted into gear. An easterly breeze will probably modify readings in the immediate
vicinity of the lakefront with shoreline lake water temperatures at 50 degrees.

On Monday a cold front is forecast to move out of the Rockies into the Central Plains
and head this way. Southerly winds will stream north from the Gulf of Mexico and
Texas, bringing a quick warm-up to the Midwest as well as an increase in dew points
(a measure of moisture in the air). Ahead of the cold front, showers and
thunderstorms will move into Illinois Tuesday. Temperatures then moderate the
remainder of the workweek, but still run slightly above normal.

COOL DOWN AND POSSIBLE LAST FREEZE NEXT WEEKEND
The average date of the last spring freeze in the Chicago area generally runs from
mid- to late April, so the cold air indicated for this coming weekend could be the last
or certainly one of the last opportunities for freezing temperatures in northeast
Illinois this spring.

What a change in Chicago’s weather the past three days. Until Wednesday, area residents
couldn’t buy a 70-degree temperature. It seemed it would never get warm. But as part of
this spring’s most stunning weather reversal, Friday brought a third-consecutive day with
readings in the 70s over a majority of the Chicago area. This weekend will produce highs
over much of the area 20- to 25-degrees warmer than a week ago. The 75-degree high at
O’Hare and 76 at Midway on Friday were the warmest readings of 2008. In contrast, North
Shore communities from Highland Park to Waukegan and Kenosha shivered in 40s and
50s much of the day. But even there, chilly east winds finally broke late in the day,
allowing temperatures to surge in all but areas near the Wisconsin line. Cloudier weather
grips Chicago on Saturday—though not without some cloud breaks and passing sunshine.

3-INCH RAINS DOUSE SECTIONS OF WATERLOGGED IOWA
What’s left of downpours that slapped Belle Plaine, Iowa, on Friday with 3.25 inches while
drenching Waterloo with 2.39 and Ottumwa with 2.28, brings scattered showers and
possibly a thunderstorm here.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
When did the science of meteorology begin? Can you give an approximate year?
Fred Fredericks, Belle Plaine, Iowa
Dear Fred,
The earliest documents about weather, preserved on fragments of papyrus and clay, come
to us from ancient Egypt and Babylonia, and date from about 2500-2000 B.C. At about the
same time, ancient Chinese scholars had begun keeping descriptive weather journals by
about 2200 B.C., and during the Shang Dynasty in 1600 B.C., scholars attempted to
analyze weather in 10-day blocks. Later, in ancient Greece, Aristotle formalized the study
in his “Meteorologica” (340 B.C.). As you might suspect, the term “meteorology” comes to
us from Aristotle’s work. At the time, a “meteor” referred to hail, rain, clouds,
rainbows—basically any substance suspended in the air or that fell from the sky.

Warmth is a perishable commodity here in spring. With cold offshore Lake Michigan
surface water temperatures in the mid-30s to low-40s, a wind shift from the east is all it
takes to send air temperatures plummeting. That’s what happened on Thursday. Sunshine
had pushed temperatures well into the 70s for a second day over a wide swath of the
Chicago area as the afternoon arrived. Midway Airport hit 74 degrees, making Thursday
the site’s warmest day of 2008. Rockford and DuPage Airport were even warmer, with
highs of 76 degrees—and temperatures in far west suburban Rochelle and De Kalb soared
to 77 degrees. But the warmth wasn’t to last long, especially lakeside.

A TALE OF TWO SEASONS ACROSS AREA
A punishing temperature plunge commenced just past midday Thursday in the northern
suburbs. Shifting winds behind a cold front literally transformed spring to winter. First hit
were north lakeshore communities from Waukegan to Highland Park, where, by
mid-afternoon, temperatures had crashed to the upper-30s and low-40s—even with
south and west suburban readings in the 70s. The chilly air next targeted the city, where
Midway's temperature dive from 74 degrees to 54 degrees took just 3 hours.

Dear Tom,

Spring means more thunderstorms and that always causes controversy at outdoor
sports events like baseball and soccer. I maintain that such events should be stopped
as soon as thunder is heard, but many disagree with me. What is your opinion?

Samuel Widder

Dear Samuel,

I will defer to the experts on this one, and without exception they all say that outdoor
activities should cease immediately when thunder is heard. Thunder is a by-product of
lightning and if thunder is heard, lighting is also present.

Brian Bennett, a principal author of the NCAA's official lightning safety rules, says
thunder should prompt an orderly evacuation of the field and that the refuge of a safe
shelter should be sought. Furthermore, he recommends that outdoor activities not be
resumed until 30 minutes after the last rumble of thunder. It's unfortunate, but
lightning safety is very inconvenient.

Airborne dust borne on Wednesday’s 50 m.p.h. winds helped produce these
spectacular sunsets phoitographed so beautifully by Mike Frankowski of South Elgin.
Thanks for the great shot, Mike!

Tom Skilling

Photos courtesy Mike Frankowski, South Elgin

Chicagoans, deprived of 70-degree warmth for 178 consecutive days—35 more than
average—basked for four glorious hours Wednesday afternoon in the year’s highest
temperatures to date. It’s been 15 years since the city’s opening 70-degree
temperature of the season has arrived so late. Only six years since 1928 have
produced the first 70-degree reading any later. Midway, where the mercury first
reached 70 at 12:47 p.m., and O’Hare at 1:08 p.m., both topped out at 73 degrees.
Rockford managed the area’s highest reading of 76 degrees. Winds, clocked as high
as 50 m.p.h. at Lombard, helped transport the unseasonable warmth into the region,
raking much of the continent’s mid-section from Texas to Ontario in Canada. The
winds whisked dust aloft off bare fields, lending the skies over Chicago a slightly
orange hue.

YEAR’S STRONGEST SUNSHINE YET
The day’s uninterrupted sun was filtered through some thin, high clouds, but still
managed the strongest ultraviolet intensities of 2008. A dermatologist, Dr. Bryan
Schultz, said it would have begun producing a sunburn on unprotected skin in just 24
minutes at 1 p.m.

Dear Tom,
My parents gave me a picture that was taken on our farm in Manteno, Ill. after a mid-
April 1961 snowstorm. Do you have any record of this storm?

Janet Sorensen, Wilmington, Ill.

Dear Janet,
Your picture, which has been posted on our weather blog at www.wgntv.com, was
taken after one of the heaviest late-season snowstorms to ever hit northeast Illinois.
The storm began late April 15 and continued into the early morning hours of April
17, bringing the area 5-8 inches of heavy, wet snow. Strong winds piled the snow
into 6 foot high drifts. The Chicago area measured 6.8 inches of snow while south of
the city near Manteno, Kankakee received 5.6 inches. Like all late-season snows, this
one did not last long. Temperatures quickly rebounded into the 60s and 70s and the
snow was gone in a day or two.

In sharp contrast to this year's long-awaited warmth, Janet Sorensen sent us this picture taken on her family farm in Manteno on April 17, 1961 after one of the biggest late-season snowfalls to ever hit this area. Nearby Kankakee received 5.6 inches of snow from this storm, while the Chicago area officially recorded 6.8 inches.

Photo courtesy of Janet Sorensen

Summer-level heat reached the Plains Tuesday sending temperatures rocketing 30-
degrees above mid-April norms shattering records—some nearly 40 years old. The
unusual warmth, 50+ m.p.h. gusts and single digit relative humidities heightened
wildfire fears prompting Red Flag Warnings from Texas to the Dakotas. July-like
highs of 91-degrees at Pierre, 88-degrees at Mobridge and 85-degrees at Rapid City
—all in South Dakota— estab- lished new records.
Northern Illinois temperatures Tuesday surged to 61-degrees at Rockford and
Kankakee and 60-degrees at Aurora and Wheeling. Peak readings at Midway and
O’Hare topped out at 59-degrees, the warmest since Friday.

THIS YEAR’S WARMEST AND FIRST 70-DEGREES IN 6 MONTHS AHEAD
Chicago’s warmest temperature to date in 2008 has been just 65-degrees nearly
three and a half months ago on January 7. A high of 73-degrees Wednesday would
become the year’s warmest. Readings had already surged to 79-degrees twice by this
date a year ago.

Dear Tom,
What kind of spring did Chicago experience in 1967
prior to the Oak Lawn tornado?
Veronica Michaels

Dear Veronica,
The Oak Lawn tornado, the deadliest to ever hit the Chicago area, killed 33 people as
it raced through that southwest suburb on Friday evening, April 21, 1967. Before the
tornado, the city had been experiencing a typical spring.

March remained chilly until the middle of the month, when the last vestiges of
January’s paralyzing 23-inch “Big Snow” finally melted. March closed with several
days in the 60s and 70s. The mild weather continued through mid-April, with eight
more days in the 70s, including a 74- degree high on the day of the tornado. The
weather turned cold in the wake of the twister. Three inches of snow blanketed the
city on April 23, followed by the city’s first below freezing temperatures since March 22.

The chill’s been so relentless, many Chicagoans could be forgiven for thinking
warmth might never arrive. But it finally appears to be on the way. It will last initially
only two days—east winds and a wet storm threaten a temperature downturn late in
the week. But providing sun-filtering high and mid-level clouds don’t become too
overwhelming Wednesday, a predicted 73-degree high will mark the first time in 178
days the mercury has struggled above the benchmark 70-degree level here. Only
three times before—in 1943-44 (185 days), 1992-93 (182 days) and 1957-58 (181
days)—has more time passed between 70-degree temperatures here. This year’s tally
is more than a month past the 80-year average of 143 days between 70s recorded at
Midway Airport.

SUMMERLIKE PLAINS HEAT SIGNALS CHICAGO WARMING
Winds that howled Monday down the slopes of the Rockies and Black Hills into the
Plains were warmed as they encountered higher air pressures at lower elevations—the
so-called Chinook effect. This pushed temperatures to 82 degrees at Willison, N.D.,
Rapid City, S.D., and Billings, Mont.

-Tom Skilling

Dear Tom,

Why do the sun and moon look larger as they rise and set and are close to the
ground?

Barry Baxter, Ottawa, Ill.

Dear Barry,
Both the sun and moon seem to be larger when they are positioned near the horizon,
but it is entirely an illusion.

It's such a compelling illusion, though, that it has a name: the "moon illusion."

No single explanation sufficiently accounts for the illusion, but it probably results
from the varying ways our minds relate the size and distance of the sun and moon
when they are viewed by themselves (high in the sky) or against a backdrop of other
objects (near the horizon). The sky at the horizon seems more distant than the sky
overhead. When viewed against the "more distant" horizon sky, the sun and moon
appear larger than when seen against the "closer" overhead sky.

Pilot and regular contributor to our blog Anson Mount shares these shots of the
Chicago area he took from the air today during a flight from Bloomington to
Waukegan—including a shot of the swollen Fox River near Barrington. North
suburban areas have been hit by more the 6” of water equivalent precipitation since
March 1. For purposes of comparison, O’Hare has averaged 4.07” since observations
began there in 1959 for the March 1 through April 14 period. Great shots as always,
Anson—many thanks!!

Tom Skilling

Photos courtesy of Anson Mount, Waukegan, Illinois

Our colleague Richard Koeneman, picturde here at his home located at the 3,500 ft.
above sea level in western North Carolina’s picturesque mountains outside Asheville,
share these photos of falling Monday evening around 5:50 p.m. Chicago time.
Richard points out the snow is beginning to cover the just-blooming Forsythia bush
next to which he’s standing. It was in the 70s there only last week! Thanks for the
great shot, Richard!

Tom Skilling

Richard shares this shot with us under the deck of the house. There, a mountain
laurel is blooming in the Monday evening’s snow!

_________________________________________
LOOKING TOWARD THE SMOKIES AT 6 P.M.
By Richard Koeneman

Temperature: 34º ... The apple orchards are in full bloom in and around Asheville
and the fruit growers are worried that tonight's temperatures might wipe them out
again (a freeze last April ruined 60-90 percent of the local orchards).

About 1/2 inch of snow came down in that burst a couple hours ago. Ah, spring!
View is to the southwest.

Photo courtesy of Richard Koeneman

The warmer weather due later this week won’t arrive a moment too soon! Amanda picket
sends us these frosty morning shots taken Monday morning in northwest Indiana. She
says she is looking forward to the predicted warming and that here daisies are too.
Amanda’s cats Jenny and Tommy are pictured here in the morning chill watching a
nearby deer. Thanks for the beautiful shots, Amanda!

Tom Skilling

Photos courtesy of Amanda Pickett, northwest Indiana

The first half of Chicago's meteorological spring 2008 has been characterized by
below-normal temperatures and frequent encounters with rain and snow. Nearly 60
percent of the days since March 1 have registered temperature deficits, and numerous
episodes of precipitation have left the area's soils soggy and rivers and streams high
or in flood. The area will be treated to an extended period of mild weather in the week
ahead with a string of at least six above-normal days beginning Tuesday.

WHILE CHICAGO DRIES OUT…
With April rainfall to date already approaching 2 inches in Chicago, a dry
start to the week will be a welcome change, giving the area a chance to dry out.

…SOUTHERN CALIFORNIA BAKES
In stark contrast to Chicago's wintry weekend, longtime heat records toppled in
Southern California. Anaheim reached 102 degrees Sunday, while Los Angeles sizzled
at 96 degrees. Record heat even reached the beaches with a high of 86 logged at the
Santa Monica Pier. Other California locations that posted record highs Sunday included
99 degrees in Fullerton and 95 degrees in Long Beach.

Dear Tom,
When I was a kid, we couldn't count all the stars in the sky. Now I have to look hard to
see one. How come the change?
—J. Roberts, Batavia
Dear J. Roberts,
Triton College astronomer Dan Joyce says you can blame metropolitan lighting. Here's
Joyce's answer: "Back in 1978, I sent a 'real telescope' to 'Star Wars' creator George
Lucas, claiming that with it he could detect galaxies over 300 million lightyears away.
But it was with a caveat: I warned him that proximity to city lights would spoil the view.
"Imagine the disappointment of those of us in astronomy who seek to show off the
marvels of the cosmos, understanding that the galactic light has traversed space so
vast, only to be obscured in the last fifty-thousandth of a second as it encounters the
glare of metropolitan lighting wasted on the night sky."

Early March-like cold continues today; then northeast winds diminish, slowly turning
to the south, and temperatures begin to moderate Monday. By Tuesday winds
strengthen out of the south and significant warming begins. Wednesday Chicagoans
should experience the first 70-degree day of the season, more than two weeks
beyond the March 31 date of average first occurrence.

BRIEF DRYING AIDS SWOLLEN RIVERS
Portions of the Des Plaines, Fox, Rock, Kishwaukee and Pecatonica in northeast
Illinois are near or in flood. With no rain in the forecast until Thursday, these rivers
will be allowed to crest and begin a slow fall.

SNOWFALL’S FINAL GOODBYE?
This weekends flurries could mark the end of Chicago's snowiest snow season (60.3
inches) since the all-time snowiest winter of 1978-79 when 89.7 inches fell.

Dear Tom,
I read a book about the 1930s Dust Bowl, “The Worst Hard Time.”
It mentions a dust storm that impacted Chicago.
What exactly happened here?
—Mike Rehor

Dear Mike,

During the 1930s, Chicago along with the Plains and Midwest were in the
grasp of a combination of heat and drought known as the “Dust Bowl.” These
summers were characterized by searing heat and blowing dust, and it was
during this period that Chicago recorded many of its highest temperatures.
The dust storm of May 10-11, 1934, was remarkable. With northwest winds
gusting to more than 50 m.p.h. and relative humidity levels at a record low
13 percent, clouds of dust swept into Chicago, reducing the Visibility to
less than one mile in many areas. Officially, seven days in the 90s were
logged in May 1934 including a scorching 98 degree high on May 31.

It's been a spring like few others. Warm weather's been in remarkably short supply.
Temperatures just east of Chicago on Friday hit 70 degrees at Valparaiso and 73 degrees
at South Bend. City readings managed to spike briefly to 64 degrees at O'Hare Airport and
65 degrees at Midway Airport -- readings which tied 2008's warmest to date. It marked
only the sixth time since Jan. 1 temperatures here have topped 60 degrees -- short of the
nine 60s considered typical by now. At Midway Airport, there have been only 21 years
since 1928 with as few 60s readings at this point in the season. Friday's fleeting warmth
lasted for a few hours. Temperatures by nightfall had plummeted into the 40s -- a dive of
20 degrees in 10 hours.
BLIZZARD PARALYZES UPPER MIDWEST
A blizzard Friday crippled the Upper Midwest. Duluth, Minn., with 62 m.p.h. gusts and
whiteout conditions, ground to a standstill. Snow there stood 10 inches deep by nightfall
with up to 15 inches just to the north -- and snow was still falling. In addition, four
dozen twisters were among the week's U.S. severe weather reports this week.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune

Dear Tom,
How can animals detect weather before something happens?
Paul See, Schaumburg
Dear Paul,
Your question is representative of many that we receive concerning the ability of
animals to predict the weather. But contrary to popular belief, there is no documented
evidence that animals have that ability. Authorities from a range of disciplines agree
that animal behavior, even when it is uncharacteristic, is a response to past or current
weather, or the result of instinctive imperatives and is not based on predictive ability.
That goes for plants, too. Such conditions as an exceptionally great (or poor)
production of seeds, as with oak trees and acorns, or premature leaf coloring in the
autumn invariably result from past weather conditions or other environmental factors
and not from any predictive ability that the organism might possess.

Jan Baumgartner shares these shots of the towering cumulus clouds which swept west suburban Sugar Grove in the "mild" air which entered the area with the storm's windy "dry wedge" around 9:30 am this morning. As Jan put it in her e-mail to us:

"It was quite a dramatic scene to behold! It went from sunny skies to very dark and then sunny again in just a matter of minutes."

Thanks for the great photos, Jan and for taking the time to share them with us!

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

Photos courtesy of Jan Baumgartner, Waubonsee Community College, Sugar Grove, Illinois

The area’s second drenching of the week pauses Friday morning amid 60-degree temperatures. But both the warmth and the freedom from rain will be fleeting. Gusty thunderstorms could flare over sections of the Chicago area Friday morning as a temperature-crashing cold front sweeps the area. Showery weather’s return Friday afternoon transitions to snow showers by Saturday in a weekend likely to be the area’s coldest in three weeks.

The dry slot of the mammoth storm pounding the nation’s mid-section hovers over Chicago as Friday gets under way. This often-windy feature of large-scale storms is behind the break in steady rainfall and occurs directly beneath the strongest winds of the jet stream. It helps lend storms their comma-shaped appearance on satellite images.

FROM BLIZZARD CONDITIONS TO TWISTERS THURSDAY EVENING

The storm, which pounded 27 states overnight, had spawned 16 twisters by nightfall Thursday. One touchdown was reported around 6 p.m. in west central Illinois at Lima—close to Quincy. Blizzard conditions in Minnesota and northern Wisconsin slashed visibilities to less than one-quarter mile.

Dear Tom,

William Johnson

Dear William,

Manned, hot-air ballooning got its start on Nov. 21, 1783, when brothers Joseph and
Etienne Montgolfier launched a balloon in Paris and were airborne for 20 minutes.
Technological advances followed quickly and by the early 1800s balloon pioneers were
able to ascend high enough that the amount of oxygen in the air was dangerously thin,
giving rise to the phrase“dizzying heights.” The atmospheric content of oxygen—21
percent of dry air by volume—does not change as we go higher, but the amount of
oxygen that we can inhale diminishes because the density of air decreases with
increasing height.

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

Dear Tom,
It’s snowing and thundering here
in late March. How is this possible?

Crystal Hepner, Gary, Ind.

Dear Crystal,
Lightning does sometimes occur during
snowstorms and meteorologists have a
colloquial name for the phenomenon:
thundersnow.

It’s a rare event, occurring in the Chicago
area only a few times in a given 10-year
period. Lightning injuries have been
recorded in the area during snowstorms.
Typically during snowstorms, moist and
relatively stable air lows gently upward
over colder air; it cools as it ascends and
its moisture condenses into snow.
However, on rare occasions when a
vigorous low-pressure system is passing
across the region and it has drawn
unstable air, usually of Gulf origin, into
its wind system, the moist air will surge
into powerful rising currents that build
into bona fide thunderstorms.

Write to: ASK TOM WHY,
2501 W. Bradley Pl.,
Chicago, IL 60618
or: asktomwhy@wgntv.com

Dear readers,
In January we introduced a new weather page in the Tribune. While some readers liked the new look, others were disappointed to see the disappearance of such features as forecast maps for all seven days, expanded U.S. city forecasts, planet watch and Lake Michigan conditions.
Because of your passionate responses, we have been working on determining the best way to bring these features back. We are happy to report that, starting today, all four of the features listed above have returned. As we head into summer, we will also bring you daily pollen counts provided by Dr. Joseph Leija and sunburn times from Dr. Bryan Schultz.
We hope you like these changes. We welcome your comments as we try to provide our readers with not only the most informative weather page in the nation but one that meets all your meteorological needs.
--Tom Skilling, WGN-TV Chief Meteorologist

It's that time again! Our 28th annual Fermilab/WGN-TV Tornado and Severe Weather seminars will take place on Saturday, April 5 at noon and 6 p.m. You are invited to join us and an outstanding group of speakers at the west suburban Fermilab National Accelerator Laboratory off Kirk Road in Batavia.

Click the link below for more details on this exciting event, including the list of speakers and topics!

--By Steve Kahn, WGN Weather Center Meteorologist

Brian Smith provides us with a little background on our Fermilab Seminar that we thought you might enjoy reading:

I thought I would give you some facts on the Fermilab Seminar. This year marks the program's 28th year, 27 of those held at Ramsey Auditorium in Fermilab. Its origins date back to 1981, when I was a University of Chicago grad student and involved in Emergency Management. I wanted to have a public seminar on severe weather. Originally, Harry Volkman was going to be the media presenter , but he backed out at the last minute. I knew Tom, and asked him to be part of this seminar. He agreed. The rest is history.

The first year, 1981, was held at Geneva High School auditorium with a total of 40 in attendance. The program consisted of a tag team program of Tom and I presenting storm spotter and safety information. (You will see a picture of this program in my presentation this year).

In 1982, ESDA (Emergency Services and Disaster Agency) agencies in Geneva and Batavia wanted to sponsor the program again. This time, Rudi Dorner, then head of Emergency Services at Fermilab, asked if they could sponsor it. We agreed. The program was originally held on a Tuesday night because Tom's days off were on Monday and Tuesday. We probably had several hundred at that program. We also invited then-Chicago MIC (Meteorologist in Charge) Ray Waldman to be part of the program.

Ever since 1982, Fermilab sponsored the program. Rudi Dorner took care of the arrangements until later in the 1980s when Bill Flaherty from Fermilab took over Rudi's position.

Fermilab Visual Media Services offered their assistance around 1986. They saw us running around trying to coordinate movie films and slides and they asked if they could help. Boy, what help Fred Ullrich and his team have done over the years to assist with production in the program. They have been a great help!

The program continued to grow when we moved the program to Saturday night and Tom began advertising it on television. We also started adding more speakers, including Richard Koeneman from WSFO (Weather Service Forecast Office) Chicago and Bill Hirt from the National Severe Storms Forecast Center.

By the late 1980s we started getting overflow crowds in the auditorium (the auditorium holds 890). Overflow rooms were set up where the program was shown remotely. In the early 1990s It was then decided to have two sessions, an afternoon and evening session. Both of these sessions were well attended. Today, the afternoon session is the most popular of the two sessions. This program has sparked similar other programs to spring up across the country. We also added many different speakers that included Ted Fujita, Tom Grazulis, Ron Przybilinski, Lance Bosart, Chuck Doswell, Harold Brooks, just to name a few.

In closing, I just want to say it is great to be back again. I want to personally thank Tom, Fred Ullrich and his staff, Bill Flaherty, for all the work with this program for all of these years. I want to also thank all of the speakers in taking your time out to help spread the word on severe weather safety. I look forward to seeing you all on Saturday!

Brian Smith
NWS Omaha

Regular photo contributor Amanda Pickett shares this shot of her cat drinking in Thursday morning’s crisp sun in northwest Indiana. Great shot---thanks Amanda!!!

Tom Skilling

Photo courtesy of Amanda Pickett, northwest Indiana

Imagine her surprise when Ericka Carlson saw this cloud overhead Wednesday morning as she was out walking her dogs in northwest suburban Sleep Hollow? In sending this to us, Ericka asks “What do you make of this?? Is it a sign??? I don’t know—but it certainly makes an interesting photo! Thanks Ericka!

-Tom Skilling

Photo courtesy of Ericka Carlson, Sleepy Hollow, Illinois