EXPLAINER: April 2007 Archives

Cool winds off Lake Michigan Monday took a big bite out of the 80° temperatures which proved such a welcome treat here this past weekend. But, record breaking early season heat wasn’t far away. Nearly four dozen weather observation sites from Nebraska across Iowa and downstate Illinois—15 in Illinois alone—recorded 90° highs.
The July-level readings established new records at a number of locations. Though Chicago’s lakefront managed only a 58° high and O’Hare checked in at 67°, Pontiac—just 90 miles to the southwest recorded 90° and downstate Danville laid claim to the state’s highest temperature of 93°. Records were set Monday at Moline (89°), Springfield (88°) and Paducah (88°.) Among the warmest readings downstate were the 90° highs at Champaign, Macomb, Mount Vernon, and 91° at St. Louis.
April closed just over a degree below normal making it the first sub-normal April since 2000.

--By Tom Skilling, WGN-TV Chief Meteorologist

Overnight a cold front moved into Chicago from the north, preceded by widely scattered showers and even a few thunderstorms. Remnant showers will drift east away from the area this morning as the front becomes stationary, oriented northwest-to-southeast along a line from Rockford to Gary. Cloudy conditions and cool easterly winds will keep readings in the 50s along the lake and 60s just inland north of the front, while sunny skies and warm southwest winds will push readings well into the 80s south of the front.
Later this afternoon, the front will begin to move back north as a warm front with showers and storms redeveloping ahead of it to the north. South winds and 60° readings will cover the area tonight. Cool high pressure will take over later Tuesday and then slowly moderate as it drifts east the remainder of the week.
Dust storms in Arizona and rare wildfires in southern Georgia and northern Florida hit drier portions of the nation Sunday.
--By Paul Dailey, WGN Weather Center Meteorologist

Strong southwesterly flow will push temperatures into the 80s over most of northeastern Illinois today. Monday could see a cold front move into southern Lake Michigan bringing a cooling NE wind and a chance of showers into the north side of Chicago to the Wisconsin border. However the remainder of the metro area to the south and west should again experience the SW winds and mid-80s temperatures. As the jet stream pattern changes from an west-east flow along the U S—Canadian border to a strong northwest-southeast flow over the western Great Lakes, low pressure will move out of the northern plains through Wisconsin into Lower Michigan Tuesday. Showers and thunderstorms should accompany the associated cold front with sharply colder temperatures on the heels of following northeast winds. Wednesday will be the coldest day this week with slowly moderating temperatures into next weekend.
--By Paul Dailey, WGN Weather Center Meteorologist

It’s been a long week for area sunshine enthusiasts. Chicagoans have been subjected to four cloudy days, 2-4” of rain and the metro area’s first tornado touchdown of the season—albeit a small one—in the Plainfield/Bolingbrook area around 3 p.m. Thursday afternoon. April’s logged just 42% of its possible sun. That’s a tally which is 11% below normal, enough to make it the cloudiest April since 1995. With all the clouds, it’s little wonder 63% of days this month have been cooler than normal. Daytime highs so far this month have averaged 10 degrees below the same period a year ago.
The sun returns Saturday, but a southeast-bound upper air disturbance and daytime heating could tap the 0.75” of evaporated moisture in the atmosphere to ignite spotty afternoon thunderstorms.
Temperatures stage a 20-degree rebound this afternoon into the lower 70s. What’s more, the low 80s predicted Sunday are likely to make this the second consecutive weekend to post 80°-plus highs.
--By Tom Skilling, WGN-TV Chief Meteorologist

Residents of Plainfield and nearby Bolingbrook, 35 miles southwest of Chicago’s Loop, suffered a scare Thursday afternoon as the fourth twister to affect that area over the past 23 years touched down at 2:59 p.m. But unlike the devastating tornado which struck with deadly consequences on Aug. 28, 1990, Thursday’s twister lasted just minutes and produced winds a fraction as strong. A National Weather Service storm survey team headed by meteorologist Jim Allsopp determined the twister was so weak it registered “EF0” on the new Enhanced Fujita storm intensity scale—the lowest possible ranking. Winds in such a tornado would only have reached 65-85 m.p.h..
The storm, which ripped a section of roof off the Lakewood Nursing Home in central Plainfield upon touchdown, managed to flip several cars. Lawn furniture was tossed through the air, but there were no reported injuries.
--By Tom Skilling, WGN-TV Chief Meteorologist

Tornadoes touched down briefly across five counties of central Illinois between 2 and 5 p.m. Wednesday. The touchdowns occurred southeast of Springfield. Preliminary reports through late Wednesday evening indicated limited damage and no apparent injuries. But, the twisters served as a reminder that April is the region’s most active tornado month. Thundery downpours threaten Thursday morning’s rush hour. But, daytime heating to Chicago’s south, cold air aloft and diverging jet stream winds threaten to support new thunderstorm development later Thursday. The environment in which these storms may erupt could support rotation—a harbinger of severe weather including tornadoes. Weather watches may become necessary over parts of the area. Wednesday’s downpours, the heaviest in 5 months, totaled 3.01” at Romeoville, 3.00” at nearby Joliet, 1.88” at Oak Brook and 1.61” at Midway Airport. ---By Tom Skilling, WGN-TV Chief Meteorologist

A wide swath of the Chicago area appears headed for a 2”+ rain in coming days, the heaviest to fall in a single storm here since 2.19” hit O’Hare five months ago on Nov. 29-30. The deluge brings to an end 11 days without measurable precipitation at the city’s official O’Hare rain gauge—the longest such period in April over 137 years of weather observations. The potent spring storm had unleashed nearly two dozen twisters Tuesday across four states—from Colorado and Texas north to Oklahoma and Kansas. The system’s downpours were so heavy across Nebraska Tuesday, the city of Kearney was swamped by 4.91”, and a number of daily precipitation records perished. The storm’s cold back side generated 22” of snow at the 8,700 ft. level near Rosita, Colo.
Chicago’s downpours will come and go Wednesday and Thursday but may be most concentrated Wednesday morning/early afternoon and again Wednesday night into Thursday.
--By Tom Skilling, WGN-TV Chief Meteorologist

Chicagoans enjoyed instant summer on Sunday as gusty south winds sent temperatures soaring into the lower 80s under bright sunshine. Readings approached or topped the 80º mark across the entire metropolitan area —including the lakefront where Northerly Island reached 81º.
Sunday’s warmth will be fleeting, however, as gathering storm clouds to the west herald the arrival of a cold front that will send temperatures tumbling, setting the stage for a blustery, cool and wet week dominated by brisk east winds. With ample moisture to feed the series of low pressure centers expected to traverse the Midwest the next several days, substantial amounts of rain could fall here this week, changing the dry nature of an April that to date has totaled only a little more than half of its normal rainfall.
Severe thunderstorms brought hail and gusty winds to southwest Iowa Sunday afternoon with quarter-size hail at Shenandoah and wind gusts to 58 m.p.h. at Atlantic.
--By Steve Kahn, WGN Weather Center Meteorologist

It will only be a one-day stand, but all factors point to Chicago recording it’s first 80º day of 2007 Sunday as gusty southwest winds push the mercury into summer-level territory for the first time since last Oct. 3 when the mercury peaked at 82º. Dermatologist Dr. Bryan Schultz warns that despite it being only April, the sun’s intensity is sufficient to produce significant sunburn, and sunscreen needs to be applied just as it would be during the summer.
Sunday’s warmth will help fuel thunderstorms that should arrive here Sunday night as a cold front approaches. The same system triggered severe thunderstorms Saturday from Minnesota to eastern Colorado and the Texas Panhandle with more than fifty reports of hail and at least five tornadoes through early evening.
The rest of the week here should trend cooler and wetter as several weather systems pass through the Midwest.
--By Steve Kahn, WGN Weather Center Meteorologist

A swarm of deadly tornadoes ripped across the Chicago area 40 years ago on Friday afternoon April 21, 1967 ravaging Belvidere and Oak Lawn. A fast-moving squall line unleashed the twisters—an outbreak which remains to this day this area’s deadliest. The storms resulted in 58 fatalities. The Oak Lawn twister continued across the Dan Ryan Expressway at the height of the evening rush hour, knocking a semi off an overpass, before proceeding out over Lake Michigan.
More recently, another tornado leveled half of downtown Utica, Ill., including 100 homes—on April 20, 2004. Eight perished when the 100-year-old building housing the Milestone Tavern collapsed during the storm. April has produced more Chicago-area twisters than any other month.
Saturday’s unlimited sunshine—the 2nd consecutive 100% sunny day—was only the third of the past two months. Temperatures surge into the 70s—then approach 80° Sunday.
--By Tom Skilling, WGN-TV Chief Meteorologist

The warmest weekend since last fall is predicted for Chicago—one which may include the first 80° temperature of the year Sunday. Over the past decade, the first 80° reading of the season has occurred on or about April 19. That would put Sunday’s 80° about on schedule. The last time a weekend was as warm as the one ahead was 7 months ago on Sept. 16-17 and the last time a daytime high hit 80° here was Oct. 3—over a half year ago.
Despite the vigorous atmospheric warm-up, Lake Michigan’s surface water temperature is at its coolest level for this date in 4 years—a by-product of April’s chilly weather.
While the atmosphere has entered a warming mode here, the snow is flying in Montana and a chill is settling over much of the West. At Box Elder, Mont. snowfall Thursday measured 16”. Snows reached 13” at Moss Peak and 6” at Lewiston—both in Big Sky Country.
--By Tom Skilling, WGN-TV Chief Meteorologist

The chilly winds which greet Chicagoans Thursday are doing what April winds have done over the years nearly half (42%) the time here—blowing from the east. March, April and May mark the heart of Chicago’s so-called lake wind season—a period in which “cooler by the lake” is a refrain all too often included in area forecasts.
These east winds come off chilly Lake Michigan. The lake’s waters warm frustratingly slowly. That’s because water exhibits a property engineers refer to as thermal inertia—the tendency of a substance to pretty well maintain a given temperature for a protracted period even as warming occurs around it.
Wednesday’s high marked the 10th time in April daytime temps have failed to break above 50°. That had happened only two times during the same period a year ago. Though chilly here, temps soared to the west—reaching 74° at Williston and 71° at Bismarck, both in North Dakota.
--By Tom Skilling, WGN-TV Chief Meteorologist

Temperatures surged into the 70s over much of the metro area Tuesday. The warm-up ended the 13 consecutive days of temperature deficits responsible for this April’s ranking as the chilliest in 28 years. Readings hit 70° at O’Hare and 72° at Midway—but it was the 75° high at Romeoville, Gary and Kankakee which topped Tuesday’s charts. Almost cruelly, the flirtation with spring didn’t last long. A back door cold front, draped across the Lake Michigan shoreline through the morning, began rushing inland as daytime heating reduced air pressures encouraging chilly, dense lake air to rush inland. Initially light winds turned into temperature crashing 30 m.p.h. gusts once the front began to move and the area’s sixth day this year above 70° was soon history. O’Hare’s temp dropped from 70° at 1 p.m. Tuesday to 52° only an hour later. But, the largest pullback occurred at Gary where temps plunged 27° from 75° at 2 p.m. to 48° by 7 p.m.
--By Tom Skilling, WGN-TV Chief Meteorologist

Tuesday’s brief temperature surge is to end suddenly this afternoon. A back door cold front—one which “backs” into the Chicago area off Lake Michigan rather than approaching from the west—threatens a precipitous temperature drop and the arrival of gusty NE winds, not unlike the plunge two weeks ago when temperatures crashed as much as 22° in a single hour—ultimately to fall from 70° back to the 40s. Fronts like today’s pick up speed as they sail down the lake. That happens because sunshine heats the ground away from the lake which in turn transfers some heat to the air just above it which becomes buoyant and rises. Air pressures drop when this happens and the colder, denser air which hugs Lake Michigan’s chilly surface begins rushing inland with increasing speed. The process is a fixture of spring here and notorious for producing sharp temperature pullbacks. --By Tom Skilling, WGN-TV Chief Meteorologist

The sun came out Sunday, pushing highs into the upper 50s over much of the Chicago area for the first time in a couple weeks.
However, the eastern third of the nation remained under the influence of the monster nor’easter hammering the East Coast. High wind warnings were out Sunday for the entire eastern seaboard from Florida to Maine. Flood and winter storm warnings were widespread from West Virginia throughout New England. Tornado, hail and damaging winds were reported in Florida and the Carolinas. Flooding occurred over eastern Pennsylvania and New Jersey, where over 4 inches of rain had fallen—and more was on the way. Heavy snows exceeding 10 inches were reported in Vermont and inland New York with the coldest air and strongest part of the storm poised to hit Monday.
Later this week, the nor’easter will retreat into the northern Atlantic, and warm south winds will flow into northeast Illinois.
--By Paul Dailey, WGN Weather Center Meteorologist

Most of the eastern third of the nation is blanketed by clouds generated by a strengthening low pressure system that will move off the Maryland-Delaware coast and further intensify over water as it tracks northeast hugging the coastline today. Flood Watches as well as Winter Storm Watches and Warnings for heavy snow are in effect over New England. Coastal flooding not seen for 15 years will result from strong east to NE winds gusting over 50 m.p.h. pounding the eastern seaboard with a surf that is already under high astronomical tides associated with the new moon. Inland along the coastline heavy rains of 2 to 5 inches will create additional flooding of rivers and streams from south of Washington, D.C. through eastern Pennsylvania and New York all the way north to eastern Maine. Heavy snow will fall in the colder air further inland with a band of a up to a foot or more forecast from northern Pennsylvania through central New York to western Maine.
--By Paul Dailey, WGN Weather Center Meteorologist

Forecasters are warning Mid-Atlantic and Northeast U.S. coastal residents that a major late-season nor’easter is on the way later this weekend. The coastal flooding it threatens to unleash from New Jersey north to Maine Sunday into Monday could be the worst since a December storm lashed the region in 1992. The storm, which buried sections of eastern Colorado and western Kansas under up to 18” of snow, is behind Saturday’s cloudy skies in Chicago and waves of violent thunderstorms that swept Texas and Oklahoma late Friday—tea-cup-sized hailstones hammered the Dallas/Fort Worth area.
As the storm makes contact with the Atlantic Sunday, explosive intensification begins as evidenced by crashing central pressures. Readings may sink to 982 mb (29.00” of mercury)—equivalent to some hurricanes. Winds rushing into the storm will surge to 60-70 m.p.h. on the Northeast coast Sunday and Monday generating 15-18 foot seas.
--By Tom Skilling, WGN-TV Chief Meteorologist

Friday’s sunshine-driven temperature “surge” to a predicted high of 50° doesn’t begin to approach the 80° warmth Chicagoans enjoyed a year ago. The city was in the midst of a spell of unseasonable warmth which included five consecutive highs well above 70° from April 10-14.
April 2007’s temperatures couldn’t be more different. Not only are the opening 12 days of the month running 10° below the same period a year ago, Thursday’s 38° high—a February level reading—marked the fourth time this month daytime readings have failed to reach 40°. Only five Aprils since the city’s O’Hare observation site opened in 1959 have produced as many or more sub-40° April highs. In fact, the past 7 Aprils combined only managed five days that cool. Less than two days since the Midwest found itself in the grip of a major spring storm, another dangerous system is moving into the Plains.
--By Tom Skilling, WGN-TV Chief Meteorologist

Snow on a par with Wednesday’s 3.0” accumulation at O’Hare is exceedingly rare in April. In fact, snowfall of 0.1” or more--what’s referred to as measurable SNOW by meteorologists—has occurred only 66 times beyond April 11 in 123 years of official snow records since winter of 1884-85. That means less than 2% of the metro area’s measurable snows have occurred this late in the season. While Wednesday’s 3” total was not an especially large amount, it marked only the sixth time a late season accumulation of that magnitude has occurred.
Warmth did eventually change rain to snow Wednesday, but not before as much as 4-6” covered Chicago’s northern suburbs amid howling easterly winds which downed powerlines and some trees. Mundelein in Lake County was hit by 5.6”—the area’s heaviest. But Wisconsin was hit even harder. Milwaukee’s 7” total broke a record for April 11 and nearby Brookfield, Wisc. was buried beneath 8.0”.
--By Tom Skilling, WGN-TV Chief Meteorologist

Chicago is to be spared the bulk of a wind-whipped, heavy, wet snowfall expected to bury sections of Wisconsin under as much as a foot of snow Wednesday. A shift to snow will take place in the city, but only briefly as colder NW winds take hold late Wednesday night. The unseasonably cold April storm crossing the Midwest has prompted winter storm advisories across 11 states.
Chicago is to be drenched by well over an inch of cold rain riding powerful 35 m.p.h. NE wind gusts Wednesday. But, temperature profiles indicate the first 7,500 feet of the atmosphere above Chicago is to remain at or above freezing—hardly an environment which supports sustained snowfall. Some of that 32°+ “warmth” is a product of easterly winds in contact with Lake Michigan’s 42° waters. Some pockets of sub-freezing air may still occur which could support a few passing spells of mixed wet snow or ice pellets (sleet).
--By Tom Skilling, WGN-TV Chief Meteorologist

For a seventh day, Chicagoans must deal with the chilly temperatures brought on by a sprawling air mass which has been draped across the eastern two thirds of the U.S. Though the chill’s intensity is slowly beginning to ebb, the 32.2° average temp here the past 6 days makes it the coldest April 4-9 period of the past 25 years and the 4th coldest such period of the 137 years since 1871. Cubs fans experienced the chill first hand at the team’s home opener. With flurries in the area, temperatures peaked at just 41° making it the coldest opener of the past 3 years. And, in a truly rare meteorological twist, temps since April 4 have been 7.5° colder than January’s opening week!
The chill has established a host of new late season cold weather benchmarks nationwide. Jacksonville, Florida’s 31° Sunday morning low marked the latest freeze on the books there. Meantime, the 6-day snow tally at Painesdale, in Michigan’s U.P., climbed to 64.5” Monday.
--By Tom Skilling, WGN-TV Chief Meteorologist

Forecasts leading up to Monday afternoon’s Cubs home opener at Wrigley Field have consistently been calling for chilly weather with the temperature hovering around 40º, but it now appears that some snow flurries could occur during the game, courtesy of a weak weather disturbance rotating through the region.
The late-season cold snap that has been gripping Chicago along with much of the eastern two-thirds of the nation is showing some subtle signs of moderation here, just before the arrival of a midweek storm system. As a result, the latest trends of numerous computer models point to the Chicago area receiving mainly rain from the storm, though areas not too far to the north and west could get hit with a spring snowstorm. With colder air returning in the storm’s wake, precipitation could change to snow before ending here Wednesday night.
--By Steve Kahn, WGN Weather Center Meteorologist

It won’t be as cold as Saturday’s record-tying 32º low maximum but if Easter’s forecast high of 38º verifies, Chicago will record its coldest Easter since the 33º high on March 26, 1978. Temperatures will rebound a bit Monday, but it should still be a very chilly Cubs home opener with highs only reaching the lower 40s.
Chicago’s chill will linger through much of the upcoming week as an approaching storm system takes aim on the Midwest. The storm will likely bring a significant late-season snowfall to areas to our north and west and current computer forecasts of the rain/snow dividing line place it perilously close to the city.
Chicago is not alone in the April cold snap. Record lows and record low maximums tumbled Saturday across the South and Southeast and frost/freeze advisories are posted all the way from Texas to north Florida threatening disaster for crops well advanced by last week’s 80º+ weather.
--By Steve Kahn, WGN Weather Center Meteorologist

Friday’s 36° high—a reading equal to the normal high on Feb. 18 and 18 degrees below current normal highs in the mid 50s—was Chicago’s coldest April 6th temperature in 25 years. On only five occasions have temperatures for the date been colder in 137 years of weather records. A wintry overcast and blustery northwest winds are likely to further reduce area highs Saturday, challenging the 71-year-old record low maximum temperature of 32°.
The outbreak of unseasonable cold is so expansive, 21 states south to Alabama and Georgia have been placed under freeze advisories, which extend into Saturday night. Low temperatures as far south as north Florida are to drop near freezing.
In stark contrast, warmer than normal readings broke records over western North America from Oregon and Washington north to Alaska. Seattle topped out at 79° while King Salmon, Alaska, hit 58°—some of the earliest 50°-plus warmth on record there.
--By Tom Skilling, WGN-TV Chief Meteorologist

April’s comparatively strong sunlight takes a bit of the edge off the February level chill Friday. Peak temperatures, which usually reach the mid 50s this time of year, are to register double-digit deficits for a third consecutive day. The chill as well as wind velocities are likely to strengthen a bit Friday night and Saturday. Moisture off the Atlantic rotating southwestward around a huge storm, slowed to a veritable standstill by atmospheric blocking in northern Canada, sweeps back into Chicago triggering snow flurries and some better organized snow showers beginning tonight. This assures less sunlight and puts the 71-year old Saturday record for the coldest April 7th on the books (32° set in 1936) within reach.
As Chicagoans shiver, residents of Michigan’s Upper Peninsula are shoveling. A record breaking April storm deposited up to 38” of snow. Marquette, Michigan’s 33.6” by late Thursday was the most ever for the month and more is predicted off Lake Superior.
--By Tom Skilling, WGN-TV Chief Meteorologist

There's never been anything quite like it in April across sections of Michigan's Upper Peninsula. The late season snowstorm/blizzard which began hammering the region late Tuesday morning has buried the area around Houghton, Michigan under as much as 28-38" of snow. That's the word from meteorologist John Dee who writes:

"Was a pretty mild winter, with the highlights being a big storm in early March (20"+) and now this April monster. Since it started Tuesday at 11 a.m. I have picked up 28" of snow with 22" on the ground. The Coop Observer in Painesdale (now the official reporting station for Houghton County) reporting 38" with 32" on the ground. Before this storm started the ground was bare, which in itself is a rarity for April up here. This is the largest single storm for Houghton for the month of April and we have also set a record for the month of April with these totals. It is still snowing and looks to do so through Saturday, so the record book will continue to be ammended. We have also received more snow from this storm than we did the entire month of December this year. I guess you could say this has been an "upside down" winter!"

Thanks, John, for the update!

-Tom Skilling, WGN-TV Chief Meteorologist

Photo Courtesy: John Dee

Cold weather is hardly a novelty here in April. But, the 35° plunge in high temperatures from Tuesday’s 70° to Wednesday’s 35° is the biggest of the past three decades to hit the Chicago area in April. It ranks among the five most impressive “day to next” April high temperature retreats to occur since weather records began here in 1871.
The cold air’s invasion of the Upper Midwest helped ignite a blizzard which paralyzed sections of northern Minnesota, far northern Wisconsin and Michigan’s Upper Peninsula late Tuesday and Wednesday, producing record snowfall. By late Wednesday, 21.7” had accumulated at Marquette, Mich.—the city’s third biggest April snow tally since official records began there in 1960. Rockland, in Michigan’s U.P., reported 25” by nightfall-and snow was still falling. The 12.7” total at Duluth, Minn. was that city’s heaviest April snow since 1870.
--By Tom Skilling, WGN-TV Chief Meteorologist

The most impressive early April cold surge in literally years hits especially hard Wednesday. The 33° plunge since Tuesday’s 70° high will be hard for many Chicagoans to take in stride. That’s because of the number of warm 70° days which have preceded it. Tuesday’s 70° was the year’s fifth. It’s been 61 years since that many (or more) 70° readings have been logged this early in the year—a benchmark last exceeded in 1946 when six 70s had occurred by now.
A 30° or greater day to next April plunge in high temperatures isn’t a frequent occurrence here. Such a pullback hasn’t occurred here since April 3-4, 1996 when daytime highs retreated from 70° to 37°—ironically, a decline identical to the one underway.
Powerful winds sweeping around the backside of a powerful spring storm deliver Wednesday’s chill. Gusts are to reach 35 m.p.h. at times.
--By Tom Skilling, WGN-TV Chief Meteorologist

Potentially dangerous thunderstorms threaten for the second time in three days. Milder, more humid air in the “warm sector” of a powerful early spring storm has rushed into Chicago on SW winds overnight in the wake of a warm frontal passage. Of concern to forecasters is the rapid descent of temperatures with height, converging winds along an incoming cold front and diverging winds aloft—an indication air is rising on a broad scale. This atmospheric combo encourages thunderstorm growth. Shifting wind direction with height causes such storms to rotate—much as the t-storm cell responsible for Saturday night’s devastating Carol Stream microburst did before sending a powerful blast of air through the west suburban community.
The unseasonable chill which plunges over most of the Lower 48 east of the Rockies in coming days threatens Chicago with its coldest early April outbreak since 1996.
--By Tom Skilling, WGN-TV Chief Meteorologist