EXPLAINER: 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.

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.

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.

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

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.

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

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.

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.

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.

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

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

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

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.

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.

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.

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

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.

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.

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

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

--By Steve Kahn, WGN Weather Center Meteorologist