EXPLAINER: February 2007 Archives

The notoriously volatile weather of March is on full display as the new month opens. Chicagoans can expect a jarring and very windy transition from Thursday’s occasionally thundery downpours to the wind-whipped snowfall expected to sweep into the area amid falling temperatures Thursday night into Friday. Any bursts of heavy rainfall have little choice but to run-off into ice-clogged rivers Thursday or stand in puddles. Area soils are frozen after a February that finished 10th coldest since 1871, averaging nearly 10° below the long term 137-year average. Frozen soil blocks percolation of moisture into the soil and the snowmelt brought on by Thursday’s milder than normal temps only complicates matters by contributing to run-off.
The atmospheric set-up becomes ripe for powerful wind gusts and falling temps Thursday night. Accumulating snow is likely to blow and drift Thursday night and Friday.

--By Tom Skilling, WGN-TV Chief Meteorologist

La Nina is on its way in the equatorial Pacific, a development which increases the odds of a wetter than normal spring here and boosts the potential for an active Atlantic hurricane season. Official confirmation of the transition to La Nina was issued by the National Ocean and Atmospheric Administration (NOAA) Tuesday. Computer climate models have predicted a rapid decline in Pacific ocean temperatures west of South America for some time. Predictions of that cooling have become even more emphatic in recent weeks signaling La Nina’s return. It was just months ago warmer than normal waters and weaker than usual easterly trade winds indicated the presence of an El Nino, which may well have contributed to our mid-winter warmth. Only one in 5 El Ninos dissipate as fast as this year’s. A slight majority of the 23 La Ninas observed since 1946 have been accompanied by wetter than normal springs in Chicago. --By Tom Skilling, WGN-TV Chief Meteorologist

The cold, snowy weather of February 2007 has extinguished a once formidable 6.4° winter temperature surplus and done so with remarkable speed. What was once one of the 9 warmest winters on record in Chicago only 6 weeks ago will go down in the books with a meager 0.1°surplus as the season closes Wednesday night—a statistical “wash.”
Not only has February been cold, it’s been snowy. The weekend’s 3.0" at Midway and 4.5" at O’Hare brings each observation site’s February snowfall to 21.1" and 20.1" respectively—nearly three times the monthly norm. Midway’s tally ranks 4th heaviest of all Februarys since 1929.
The weekend storm spared Chicago the blow it delivered in terms of snow to Wisconsin and Minnesota. Had the 1.13” of moisture delivered by the weekend system been snow here, more than a foot would have fallen. North and west suburbs recorded the largest snow totals —including 11.4" at Antioch.

--By Tom Skilling, WGN-TV Chief Meteorologist

After a morning of fog and rain, a quick burst of heavy snow that brought up to 2 inches to some areas swept into Chicago from the southwest Sunday afternoon. Cold air wrapping around the exiting storm’s low pressure center dropped temperatures that had risen to 40º in some areas back to the freezing mark.
With the upper low pressure center holding just north of the area until Tuesday, more bursts of snow are possible here as disturbances pass through, and each of these bursts could bring some quick 1-to-2 inch accumulations until the system finally departs later Tuesday.
The last week of meteorological winter looks like it will be a cold one with highs mainly in the 30s, through brief warming on Thursday could bring some low 40s along with some showers.
Another shot of cold and snow showers will follow this system for meteorological spring’s opening weekend with highs holding in the 30s.
--By Steve Kahn, WGN Weather Center Meteorologist

The Chicago area was reeling after a veritable smorgasbord of winter weather blasted the region Saturday night with every type of winter precipitation imaginable. Snow was predominate in the northern suburbs, while areas to the south vacillated between freezing rain, sleet and snow. Thunder and lightning accompanied the precipitation early Saturday evening with reports of thundersnow across a broad area from Palatine to DeKalb, and from Aurora to Joliet. The southern suburbs also received considerable freezing rain with more than a half inch of ice wreaking havoc with trees and power lines while making travel treacherous.
Saturday evening’s onslaught was but the opening round of a late winter storm that is expected to last into Monday. As colder air wraps into the system, the precipitation should change to all snow during Sunday, continuing in waves of varying intensity into Monday before ending.

--By Steve Kahn, WGN Weather Center Meteorologist

The season’s third major winter storm—the second in February—lambastes the northern half of the Chicago area, from the city north beyond the Wisconsin state line, beginning late Saturday. While rain and sleet rather than snow pepper south suburban areas, accumulating snow and sleet whipped by 35-40 m.p.h. gusts threaten overnight conditions which may degenerate to near-blizzard status, especially in open areas. Wisconsin travel is to become truly challenging. There, 12-16” accumulations are possible.
Lightning flashed across much of Iowa late Friday in heavy showers of sleet—a condition which may well be replicated across sections of the Chicago area Saturday night. Lightning has been officially recorded during snow in February only once here—on Feb. 8, 1891.
Warmth—including 70° and 80° readings beneath this storm’s southern flank—produced tornadic t-storms in Texas Friday. A touchdown was reported near McLean in the state’s Panhandle.
--By Tom Skilling, WGN-TV Chief Meteorologist

No February in Chicago has hosted two 10"+ snowstorms. That’s why a new storm responsible for winter weather advisories across 18 states including northern Illinois, is being monitored so closely. It’s possible this system could deposit that much or more snow over at least sections of the metro area, though much can change. The new storm is likely to begin unleashing precipitation on the area by Saturday afternoon as snow or sleet. Though temperatures are close enough to the rain/snow threshold, an extended snow/sleet/freezing rain mix could cut into any snowfall. The consensus of 28 computer models is that an average of 1.49" of precip may fall (water equivalent), and as much as 75% of it could fall as snow. That would make an 8-10" weekend accumulation entirely possible. The 18.1" already on the books this month at Midway Airport is 75% more than the 10.3" that falls in an entire February and qualifies as the 3rd snowiest since 1929.

--By Tom Skilling, WGN-TV Chief Meteorologist

Temperatures soared to 50° Wednesday on Chicago’s lakefront and at Gary. The warmth sent metro area temps above 40° a third consecutive day—the first time that’s happened since early January. Despite the recent string of above normal readings, this month is averaging only 13.5° making it the 6th coldest February on record here since 1871 and the coldest February in nearly three decades. The chill has had a major effect on furnace usage. Estimates of home heating based on the month’s temps to date suggest usage has soared 36% in Chicago, a harbinger of significantly higher heating bills—a trend which has been observed across the entire Midwest. The thick fog which preceded Wednesday’s warmth slashed visibilities to 1/16 of a mile just before 7am at Midway Airport and to 100 ft. in sections of northern Indiana, where a coating of frost covered trees and other cold outdoor surfaces. —By Tom Skilling, WGN-TV Chief Meteorologist

Wednesday’s predicted 50° high not only becomes the area’s mildest temperature in six weeks but also marks a stunning 60° rebound from the depth of the just completed three-week cold wave. The chilly spell hit bottom when the mercury dove to -10° the morning of Feb. 5. The huge temp rebound has sent the meltdown of the area’s once impressive snow pack into overdrive, saturating the lowest several thousand feet of the atmosphere with the moisture which fuels Wednesday morning’s haze and areas of fog. The snow cover at Midway Airport diminished from nearly 9" early Monday to only an inch by nightfall Tuesday—an 8" loss in just 36 hours!
Tuesday’s 45° at O’Hare and 47° at Midway marked the area’s mildest readings in 39 days. But the mild temps weren’t the only sign of spring’s approach. Powerful t-storms unleashed barrages of large hail—including 1.75” diameter stones at Ullin, Ill. in downstate Pulaski County.
--By Tom Skilling, WGN-TV Chief Meteorologist

Chicago’s longest sub-freezing spell in 23 years ended Monday after a 537 consecutive hour (22 day) run which started just after 1:30 a.m. Jan. 27. A 1984-85 string of 33 below freezing days was the last time the metro area had logged so many back to back sub-32° days. The degree of warming Monday was remarkable given all the snow still on the ground. That snowpack holds as much as 0.75" to 1" of water—moisture which is likely to percolate into any patches of soil which thaw in the 40° temps expected well into the coming weekend. This could mean the heavy rains predicted in a new storm this weekend may provoke localized flooding.
Powerful near-40 m.p.h. winds were able to override a great deal of the cooling effect which typically occurs over heavily snow-covered terrain. The winds blew 40° air several thousand feet aloft down to the surface. By day’s end, the snow-eating winds had slashed Chicago’s snow cover from 9" to just 5" by nightfall.
--By Tom Skilling, WGN-TV Chief Meteorologist

With daily highs consistently above freezing, gusty evaporative winds, a good chance of snow-eating rains—especially late in the week—and a melt from soil warmth below; it’s only a matter of time before the snow cover over the area disappears. The melt will be slow the first part of the week, but a major storm is expected to develop in the central Plains midweek and move northeast. Strong southerly winds importing moisture-laden air from the Gulf of Mexico are forecast to lift over a warm front and create a steady rain over northern Illinois Friday.
Heavier showers and possible thunderstorms Saturday should just about finish off the snow cover. However, the warmer temperatures will also melt ice in area rivers and create ice jams which, combined with an inch or more of rain and heavy runoff due to the melting snowpack, set the stage for potential flooding.
Meanwhile, Florida farmers continue to fight freezing nighttime temperatures.
--By Paul Dailey, WGN Weather Center Meteorologist

It will still feel bitterly cold Sunday, but by Monday, Chicago’s transition from a three-week deep freeze to a more “normal” temperature regime will be complete. The last in a series of snow-producing low pressure systems that have continually reinforced an Arctic-cold grip over northern Illinois moved east Saturday. The cold, dry high pressure air mass that followed will quickly migrate east as the long-entrenched north-south upper flow pattern aloft completes its reversal to a strong west-east stream flow.
Instead of sweeping down from the north, low pressure systems the rest of the month will move from the west to the east along and south of the U.S.-Canadian border. This will allow intrusions of warmer southerly flow. Even though the lower Great Lakes will sit at the northern end of these warm-air surges, the net effect will be closer to “normal” readings for Chicago. Lengthening days and slowly intensifying solar radiation will also aid in the warm-up.
--By Paul Dailey, WGN Weather Center Meteorologist

Chicago’s once mild winter, which boasted a 6.2-degree temperature surplus on Jan. 18, is about to head into deficit territory. A cold air blast following the Friday night/Saturday morning Alberta Clipper system should bring another couple of inches of snow to the area and complete the city’s month-long temperature slide from 9th to 72nd mildest out of 137 winters. With that job accomplished, the cold is living on borrowed time as a milder regime is expected to dominate here for meteorological winter’s remaining two weeks.
Monday promises to bring the city its first thaw in 23 days since a 34º high on Jan. 27, and temperatures reaching the lower 40s are possible by the end of next week as the warming trend gathers steam.
The warm-up should make great strides in eradicating much of the area’s deep snow cover—but at the price of extensive cloudiness and dense fog.
--By Steve Kahn, WGN Weather Center Meteorologist

Another low pressure “Alberta Clipper” system is headed this way out of the Dakotas. It should pass through Illinois tonight and early Saturday depositing a new 1 to 3-inch layer of snow over northeast Illinois. The last in a long series of almost continuous cold air surges out of Canada will follow, holding Sunday’s high temperatures in the teens with gusty northwest winds producing sub-zero wind chills once again. However a major shift in the jet stream is expected early next week with a west-east flow pattern expected to evolve over the United States, confining arctic air to central and northern Canada. A warming southerly flow will finally work it’s way back into the Midwest producing rain ahead of an approaching cold front later Monday and Tuesday. Despite very strong south winds, the extensive snow cover will hold temps in the low to mid 30s; however once rain is added to the mix, snows should melt quickly and rivers swell. --By Paul Dailey, WGN Weather Center Meteorologist

Snowfalls as heavy as this week’s are remarkably rare in Chicago. It’s only the 14th time since snow records began at Midway Airport in 1928 a snowstorm has socked the site with a foot or more of snow. The 12" measured as the final flakes fell at 1:08 p.m. Wednesday is the heaviest to fall in a February there since 12.3" fell on the 6th and 7th of the month in 1933—74 years ago.
Just west, O’Hare’s 10.3" tally was its heaviest this season and established a new Feb. 13 record. But, that total was dwarfed by the 14.6" reported at Whiting, Indiana, 12" in west suburban Batavia, 11.2" at Morton Arboretum and 11" at Arlington Heights and Oak Brook.
Snow fell over 36 consecutive hours amid gusts in 31 of them which hit 39 m.p.h. and produced 5 ft. drifts. Snow slashed visibilities under a quarter-mile for 8 hours. February’s 15.9" at Midway ranks 3rd snowiest since 1928.
--By Tom Skilling, WGN-TV Chief Meteorologist

Bursts of lake-effect snow extend to 30+ hours and a third consecutive rush hour, one of the city’s most impressive February snows. Calendar day snows in excess of 6" have occurred in February only 24 times dating back to 1885. This storm’s final snow tallies are likely to finish in the 6 to 14" range over much of the metro area. Only areas closest to the Wisconsin line are to log substantially less—3-6”.
The storm’s first flakes fell at Midway Airport beginning at 1:42 a.m. Tuesday morning and built quickly to whiteout proportions in the howling NE winds which went on to generate drifts 3 to 5 ft. high. Gusts reached 39 m.p.h. Tuesday at Midway. But, velocities approaching 50 m.p.h. at the city’s offshore Harrison/Dever Crib (3 miles out in the lake) offered a more accurate glimpse of the raging, blizzard-strength gusts which raked Chicago’s lake front. For hours at a time Tuesday afternoon, visibilities dropped to 1/4 mile or less.
-By Tom Skilling, WGN-TV Chief Meteorologist

Late winters in recent years have been so void of anything resembling a snowstorm, that Tuesday’s predicted 4-8" of wind-driven snow could enter the books as the city’s biggest February snowstorm in 7 years. Only one February snow event here since 2001 has managed to exceed 2". The last really impressive February snow hit on Feb. 18, 2000, dumping 11.1".
Powerful NE winds here Tuesday, produced by the huge spread in air pressures between a sprawling arctic high to Chicago’s north (30.86") and the intensifying winter storm center to the south, deliver the day’s snow horizontally and threaten to blow and drift snow, creating near blizzard conditions in open areas.
Snowfalls ranging from 2-4" near the Wisconsin border, 4-8" in the city and as much as 10-14" in hardest hit far south suburban areas and downstate, arrive in the 17th least snowy winter at Midway Airport since 1929.

-By Tom Skilling, WGN-TV Chief Meteorologist

The mild opening of winter 2006-07 has all but been forgotten. The persistent cold that has gripped Chicago since late January shows no sign of letting up as another round of subzero weather heads for the city later this week. However, before the cold arrives, Chicago is in store for some significant snowfall—one aspect of winter weather that has been relatively scarce so far. A complex storm system is taking aim at the Midwest and may bring a foot or more of snow to southern portions of the metropolitan area by the time the final flakes fall here on Wednesday morning.
Chicago is not alone in facing the upcoming storm. A variety of winter storm watches and warnings are posted in advance of the late-winter system for more than a dozen states from the central Plains to the middle Atlantic Coast. In addition to heavy snow, ice will be a problem on the storm’s southern flank, and parts of the Northeast may be in for a full-scale blizzard by midweek.
--By Steve Kahn, WGN Weather Center Meteorologist

The Chicago area will temporarily emerge from the deep freeze early this week with temperatures expected to flirt with the freezing mark Monday for the first time since a 34º high back on Jan. 27. However, the brief warm-up will be accompanied by snow and followed by a midweek return to arctic cold.
A potent storm system moving along the southern branch of the jet stream threatens to produce a major snow from the southern Midwest into the middle Atlantic states. While the heaviest snow is still expected to fall south of Chicago, successive computer runs have been shifting the storm northward, increasing the city’s threat for significant accumulations. In addition, a period of lake-effect snow should develop here Monday night and Tuesday as a new slug of arctic air sweeps full-fetch down Lake Michigan. This means more subzero weather before a new moderating trend begins and continues through next weekend.
---By Steve Kahn, WGN Weather Center Meteorologist

The past two weeks have been brutal here. Chicagoans have braved six consecutive subzero nights while Rockford (and presumably far west suburban) residents by Saturday morning will have shivered through a February record-tying eight consecutive subzero nighttime lows.
By late Friday, the stubborn arctic air mass which has gripped the area, producing a string of subfreezing days since Jan. 27, had slashed mild winter 2006-07’s temperature ranking by 50 slots—reducing it from 9th to 59th mildest of the past 137 years. The once impressive 6.2-degree Chicago winter surplus has all but vanished. The season is now only 1.3 degrees above normal, a surplus likely to keep slipping despite a brief moderation in the next few days.
For five short hours beginning at 11 a.m. Friday, Chicago’s wind chills moved into positive territory after 165 consecutive hours (nearly seven days) below subzero.
--By Tom Skilling, WGN-TV Chief Meteorologist

There hasn’t been a February in Chicago which has opened this cold in 112 years. The first eight days have averaged only 4.4°—a reading 20 degrees below the 137-year average of 24.4°. Only one Feb. 1-8 period since 1871 has been colder—and it occurred in 1895.
High clouds overnight have restrained the nighttime temperature decline a bit. The clear skies Thursday morning allowed far west suburban lows to plummet as low as -26° at Ogle County’s Rochelle, about 50 miles west of Chicago. Aurora Municipal Airport in west suburban Sugar Grove bottomed out at -17°.
For many across the metro area, Friday marks the 7th day of subzero temperatures—the longest such stretch in 13 years and one of the three longest of any winter season since official records began in 1871.
The bitter arctic air has unleashed unprecedented lake snows downwind of the eastern Great Lakes. Parish, N.Y., has measured 88” since Sunday.
--By Tom Skilling, WGN-TV Chief Meteorologist

The longer the now 12-day old cold spell goes on, the clearer its unusual nature becomes. By 9 a.m. Thursday, Chicagoans will have shivered through sub-zero wind chills 139 consecutive hours. It’s a streak which began at 2 p.m. this past Friday. Meantime, sub-zero thermometer readings greet many metro area residents a 5th consecutive morning Thursday and a 6th appears on its way by daybreak Friday. This places the current sub-zero stretch just shy of the second-longest February record of seven consecutive sub-0° readings back in 1979. The record of eight was recorded Feb. 11-18, 1875.
A mammoth arctic high extending from the North Pole south to the U. S. Mid-Atlantic and featuring an eyecatching central barometric pressure above 31.18” of mercury (1056 mb.) over northern Canada later Thursday is behind our big chill. The system has formed as air sinks on a vast scale beneath three converging jet streams.
--By Tom Skilling, WGN-TV Chief Meteorologist

The temperature in Chicago hovered at 0° as the first flakes of snow fluttered to earth around 8:35 a.m. Tuesday morning. Seven hours later, the hardest hit south and west suburban areas had measured up to 7" of snow, while 2.5" accumulated at Midway and 2.1" at O’Hare. Snowfall at such low temperatures is “airy” and brings with it special challenges. Street chemicals, lacking additives to lower the freezing point of the water into which the snow melts, act more slowly. The meltwater produced can freeze in short order, complicating the flow of traffic. (Note: Chicago has added calcium chloride to its street salt since the late 1970s to combat snow accumulations which occur at low temps.) Also, the volume of such snow is often two to three times that of snow which falls at warmer readings. That’s why moisture which in warmer conditions would have produced just an inch or two of snow fluffed into a half a foot to the city’s south. ---By Tom Skilling, WGN-TV Chief Meteorologist

The Chicago area appears headed for its first 1"+ snow accumulation Tuesday since the 1.6" which fell Jan. 15. Snow is to commence toward midday and may fall 6-8 hours before ending Tuesday night. A small but fast moving disturbance racing southeastward is encouraging milder air to blow north into the formidable dome of cold air which has dominated here since Friday, a process often referred to as “overrunning”. Snowfall in air as cold as Tuesday’s tends to “fluff up” more than usual. That’s why the modest 0.13" (water equivalent) predicted to fall by a suite of computer models may lead to 2-3 times the normal volume of snow. Rather than a 1" snow, Tuesday’s system could put down as much as 1-3" across the city—less to the north but as much as 4-6" totals south to Kankakee and Morris. Monday morning’s low reached -10° at O’Hare, the coldest temp since Jan. 5, 1999 when the low hit -16°. --By Tom Skilling, WGN-TV Chief Meteorologist

Chicago will slowly emerge from its first real encounter with cold in winter 2006-07 by midweek, after what could be as many as five straight days with subzero readings—something that has not happened here since Dec. 20-25, 2000, when six straight subzero days were logged.
While Chicago has been dealing with cold and wind chill, the Great Lakes snow belts have been pounded as the lake-effect snow machine has been running in high gear. More than 15 inches of snow has fallen in the Grand Rapids area over the weekend, with many vehicle accidents reported as a result of whiteout conditions.
Temperatures here will begin to moderate on Tuesday, finally reaching double digits. However, the warming trend may come with a price tag, as some snow is expected to fall here. Even though moisture is limited, a couple of inches of fluffy snow could accumulate here by Tuesday night.
--By Steve Kahn, WGN Weather Center Meteorologist

An arctic front passed through Chicago Saturday morning setting the mercury on a downhill run that could end up rewriting a Feb. 4 record low max of 0° that has been on the books since 1918. Saturday’s temps peaked during the morning in the 10-15º range then fell steadily, dropping below zero by evening. The arctic air mass, one of the coldest in more than a decade, could keep readings here in negative territory at least until Monday afternoon and possibly until midday Tuesday. The city’s last encounter with subzero highs was 11 years ago (Feb. 2 and 3, 1996) with back-to-back highs of -5º. Exacerbating the cold will be biting west winds that will send wind chills tumbling to dangerous levels as low as -35º. While the arctic blast in Chicago was accompanied by only brief flurries, total whiteout blizzard conditions were the rule in western Michigan Saturday where new snowfall totaled from 5-10 inches. --By Steve Kahn, WGN Weather Center Meteorologist

Only the most formidable arctic blasts are able to overcome daytime warming. Saturday’s arctic outbreak is to rank among them—even without the extensive cover of snow present with so many cold waves through Chicago’s weather history. The current cold season is the least snowy in 24 years at Midway Airport and the 8th least snowy there since 1928.
Saturday’s intensifying chill is likely to squeeze out what little moisture is available as fluffy snow which could cover the ground in spots. But, the big weather story of the next four days—particularly from Saturday afternoon through Monday night—is the bitter temperature/wind combo predicted. Dangerous wind chills of -30° to -35° are within reach during the period.
Friday’s 12° high was this winter’s coldest and the lowest temperature here since 8° last Feb. 8. At one point Friday, Chicago’s wind chill dipped to -12°, making the air here feel 103 degrees colder than Miami’s 91° peak heat index.
--By Tom Skilling, WGN-TV Chief Meteorologist

This winter is only the 17th of the past 137 on record here not to have produced a 0° temperature in the city up to this point in the season. Februarys, once prolific producers of 0° or lower overnight temperatures, produced only 21% as many 0° nights in the 1990s compared to the 1970s—28 versus 6. Only two have occurred in February since 2000. It’s a situation which is to change dramatically in coming days—a period in which five consecutive sub-zero nights appear a good bet. Chicago’s predicted temperatures the next 7 days would make Feb. 2-8 the city’s coldest such period on record here since 1871.
The chill of recent days is chipping away at this winter’s impressive temperature surplus. Since the first of the week, the season has slipped from 15th to 20th mildest as its average temperature has dropped 1°.
Ten states to Chicago’s west are being whipped by gusty winds which have prompted wind chill advisories.
--By Tom Skilling, WGN-TV Chief Meteorologist