December 2007 Archives

The subject of global warming, bubbling in the meteorological community (and elsewhere in academia) for several years, has burst controversially into the public consciousness. It’s our prediction that it will be an increasingly controversial topic in 2008 and beyond.
The Earth’s climate is changing. All evidence is that it has always done so and always will do so, but a new factor in the “change equation” is man’s role in future climatic shifts.
We have been proceeding headlong and, until now, blindly into a future of “climatic uncertainty” in the sense that there exists an unknown ratio between the benefits and costs of climate change. Decision makers need to weigh and compare the risks/costs of premature or unnecessary actions against the risks of failing to take actions that subsequently prove to be warranted. The issues are complex, but we are finally beginning to address them.

--By Richard Koeneman, WGN Weather Center Meteorologist

Air of Arctic origin swirls into Chicago Monday night and Tuesday, and the resultant temperature crash sends the city's readings from the lower 30s today to near zero, at least in the suburbs, 24 to 36 hours later.
Strong winds and light snow, too, will accompany the temperature dive. Snow flurries and periods of somewhat more sustained light snow are likely to linger through Tuesday, but this is only a nuisance snow event. Two-day accumulations of less than two inches are indicated. Of greater significance: 20-30 m.p.h. northwest winds and subzero wind-chill temperatures on Tuesday.
Elsewhere, beneficial rains spread across the drought-stricken Southeast on Sunday, putting down 1 to 2 inches of desperately needed rain. However, thunderstorm winds damaged eight homes in Liberty, Ga., Sunday afternoon.
--By Richard Koeneman, WGN Weather Center Meteorologist

In a typical December, Chicagoans can expect 9 inches of snow. That's the long-term average based on 79 years (1928-2006) of snowfall data as registered at Midway Airport. This month, however, has been among the city's snowier Decembers.
The month-to-date snow total of 18.5 inches ranks this month as the city's 10th snowiest, and the possibility of some light snow late tonight and on Monday will add a bit more to the month's final tally. This month's snow total, while more than twice the climatological expectation, poses no threat to Chicago’s all-time December snowfall record.
Think back seven years to December 2000. Forty-one inches of snow blanketed the city that month and, coupled with exceptionally low temperatures, the snow did not melt away between storms. It was a commuters' nightmare.
--By Richard Koeneman, WGN Weather Center Meteorologist

As Friday's snow-producing low pressure system moves northeast, clouds associated with the low will persist well to the west, keeping Chicago under a cloud cover today.
Assuming that clouds spread quickly back into northeast Illinois ahead of low pressure approaching from the northwest, cloudy skies will likely close out this December -- normally the cloudiest month of the year.
Because temperatures warmed into the mid 30s, yesterday's snow was wet and heavy. Snow melting upon impact and packing kept snow depths in the 2- to 3-inch range within Chicago's city limits.
This month's snowfall at Midway Airport has now reached 18.5 inches -- making this the second snowiest December of the past 28 years there. Farther to the north and west, snow totals gradually increased, reaching 6 inches along the Illinois-Wisconsin border. In the Milwaukee area, 7.5 to 8 inches were recorded.
--By Paul Dailey, WGN Weather Center Meteorologist

7.5 HOUR SNOW EVENT ENDS
The snow has ended across the Chicago area after bringing most of the city a 2-4" snowfall in just a little under 8 hours. The snow began around 8 a.m. this morning and had ended by about 3:30 p.m. Many locations in the southern portions of the metropolitan area experienced a rain/snow mix or a period of rain at the tail end of the storm. Heavier amounts of snow in the 3-5" range fell northwest of the city towards Rockford.

Some area snowfall totals
Mundelein 4.3"
Arlington Heights 2.9"
Midway Airport 2.4"
Downers Grove 2.4"
Oak Brook 2.4"
O'Hare 2.2" (official city total)

SNOW TO END THIS AFTERNOON AFTER 2-LOCALLY 6 INCH TOTALS

The snow arrived right on schedule this morning, beginning across the area around 8 a.m. Just before 1 p.m. a little over two inches had accumulated at Arlington Heights while Frank Wachowski, the Midway observer reported 1.9". The storm is moving out of the area at a fairly rapid pace and it appears that the snow will be ending during the afternoon. The storm's fast departure will limit total snow accumulations putting final amounts in the 2-5" range. The snow has been a bit heavier to the north and west where 3- 4 inches have already accumulated in the Rockford area and a few locations far northwest of the city may wind up with 6 inches.

By Chicago’s standards, today’s snowstorm is hardly a blockbuster, but it’s surely enough to please the children and simultaneously chill the hearts of area automobile commuters. Snow is likely to begin about mid-morning, thereby sparing the early morning commute, but three to seven inches of snow will blanket the area by mid afternoon and that promises a messy evening rush hour.
Falling with temperatures near freezing, the snow will have a rather high water content and constitute what is colloquially known as “wet snow.” Snow shovelers take note.
This storm system has had a history of moderate snow production. As of Thursday evening, areas east of Denver reported seven to eight inches.
Looking ahead, genuinely cold air is poised to descend on the city on New Year’s Day, bringing official sub-zero temperatures for the first time since February.
--By Richard Koeneman, WGN Weather Center Meteorologist

Vigorous weather, initially as snow and then as sharply lower temperatures, will be factors of concern to Chicagoans in the near future. The passage of a strong low pressure system across the Midwest suggests we can expect several inches of snow on Friday followed by sub-zero temperatures on New Year’s day.
The federal Bureau of Transportation Statistics (BTS) has released surprising statistics concerning the causes of passenger slowdowns in U.S. airports—including such factors as flight delays, cancelled flights, air traffic congestion and weather. BTS statistics challenge the popular notion that adverse weather is the main cause of commercial flight problems.
Surprisingly, airline issues (such as staffing shortages and mechanical problems) were, in total, greater contributors to passenger slowdowns than bad weather.
--By Richard Koeneman, WGN Weather Center Meteorologist

Sunshine, relatively mild temperatures and light winds on Christmas Day offered a welcome demonstration that interludes of decent weather, at least on a relative basis, do occur here in December. While noting that December is our cloudiest month, Chicago weather historian Frank Wachowski reports that the sun detector at the Midway Airport weather observation station has logged only 3,492 minutes of sunshine this month (through Dec. 25) versus a normal of 13,825 minutes for that period.
Santa Ana winds, an ever-recurring problem for southern California, roared through the Los Angeles area during the Christmas holiday. Los Angeles County's Whitaker Peak registered sustained winds of 55 m.p.h. with gusts to 102 m.p.h. on Christmas Eve. Nearby Malibu was buffeted by gusts to 78 m.p.h. early Christmas morning.
--By Richard Koeneman, WGN Weather Center Meteorologist

Not since 1994, when Chicago’s Dec. 25 temperature jumped to 52º, has a Christmas been milder than this afternoon’s expected high of 40º. Sunshine, too, finally returns to the city after nearly a week of cloudy days.
The sunny interlude will be brief, however, because the weather pattern remains active and another storm system, putting snow across the Rocky Mountains today, sweeps into the Midwest on Wednesday. Snow associated with that weather disturbance arrives here Wednesday night, accumulating an inch or less before heading rapidly off to the east by early Thursday.
Computer models indicate a more vigorous disturbance arrives on Friday with the potential to deliver a few inches of snow. Temperatures, though, will be critical, and a rain/snow mix is not out of the question.
--By Richard Koeneman, WGN Weather Center Meteorologist

Clouds, light snow and gusty west winds remain today, but the low pressure system that gave Chicago its lowest pressure in 20 years is moving rapidly northeast away from the western Great Lakes. A band of heavy snow lies to the west and northwest along the Mississippi River. Portions of the city proper as well as northern Indiana, lower Michigan and western Ohio are cleaning up and recovering from damage inflicted by fast-moving severe thunderstorms early Sunday. Winds in excess of 60 m.p.h. downed trees and power lines in many locations. The National Weather Service collected at least 57 severe storm reports on Sunday.
A wind gust of 88 m.p.h. was recorded Sunday at the Harrison Street Crib off the Chicago shore in Lake Michigan. The official 63 m.p.h. gust recorded at O'Hare Airport was the second highest ever at Chicago in December.
A calmer week lies ahead with clearing skies tonight leading into a sunny Christmas Day.
--By Paul Dailey, WGN Weather Center Meteorologist

By the time most Chicagoans arise, temperatures will be in the 20s and falling with snow caught up and blowing horizontally by 30-40 m.p.h. west winds. Low pressure will have passed over NE Illinois overnight with its associated cold front sweeping through the metro area between 3 and 5 a.m. Prior to the cold frontal passage, despite steady rain, south winds pushed temperatures to their highest Saturday levels just before midnight. Sunday's highs, probably near 50 degrees, will be recorded shortly after midnight. By noon Sunday, readings will most likely sink below 20 degrees -- an approximately 30-degree drop in less than 12 hours. While heaviest snow will occur well to the northwest in Wisconsin, at least 1 to 2 inch accumulations will occur here, most likely in far west and north portions of the area. Outdoor activities and travel will be hazardous while wind chills are expected to fall into single digits before noon and below zero later this afternoon and tonight.
--By Paul Dailey, WGN Weather Center Meteorologist

Were the ground completely free of snow, much of the Chicago area would be headed for 50 degrees Saturday. Mild weather's staging a temporary comeback: Not since a 45 degree high nearly three weeks ago on Dec. 2 has weather approaching Saturday's "warmth" been observed here. A winter storm, expected to intensify Saturday night on its trek from Texas to Wisconsin, sets the stage for the surging temperatures as the system's front-side SE winds pump Chicago's readings into the 40s.
The intensification predicted overnight supports strengthening winds and even several embedded thunderstorms. A potent cold front swings across the area between 3-6 a.m. Sunday, the point at which rain transitions to snow. The passage of a powerful upper storm Sunday -- which by all appearances is being inadequately handled by computer models -- could bring accumulating snow for a time. The addition of falling temperatures and howling west winds could make for a challenging day.
--By Tom Skilling, WGN-TV Chief Meteorologist

Chicago’s suddenly milder temperatures and decidedly stronger southeast winds Friday can’t hide the fact the clock is ticking toward winter’s official (astronomically determined) open. Winter Solstice takes place just after midnight at 12:08 a.m. Saturday morning—the point at which the sun’s most direct rays fall as far south on the planet as at any time of the year. Winter begins with the year’s shortest day in the northern hemisphere. Sunlight is just one-fifth the strength of June sun in Chicago, with just over 9.1 hours of daylight. The good news is days here begin to lengthen gradually and more than 5 hours of daylight will be added by the time summer begins in June.
A rare December Air Pollution Action Day has been declared by the Illinois EPA Friday. Air quality slipped to unhealthful levels at a number of Chicago area sites Thursday.
--By Tom Skilling, WGN-TV Chief Meteorologist

Hoar frost—the product of dense fog across our western suburbs in recent days—is behind these stunning scenes in DeKalb County as photographed by David Lindgren and forwarded to us. David, who farms there on the University of Illinois Research Farm, has shared spectacular weather shots with us on a number of occasions in the past and shares weather observational data with us. These shots rank among our favorites from David! Visibilities dropped below ¼ mile in that region last evening producing the picturesque coating of ice and ice crystals you see here. Thanks for sharing these with us David!

Tom Skilling

Here, in additional to the stunning frost vistas, David Lindgren tells us we’re looking at the original barn on the University of Illinois Research farm in DeKalb County.

Photos courtesy of David Lindgren, DeKalb County

Dense fog has slashed visibilities to fractions of a mile west and south of the city since late Wednesday. The tiny, supercooled (sub-freezing but still in liquid form) droplets which comprise the fog can freeze on contact with colder outdoor surfaces and care is urged while walking or driving west and south of the city where icy patches have developed overnight. The fog is trapped by a layer of warm air and resides within a shallow layer of cold, dense air not much more than a thousand feet deep. Melting snow is behind the haze and fog of recent days and nights. This atmospheric set-up, which meteorologists refer to as a temperature inversion because the normal decline of temperature with height has been inverted, is having another effect beside the haze and fog build-up. Air quality, as measured by Illinois EPA, neared the unhealthful range in Chicago Wednesday and actually moved into the unhealthful range in the Quad Cities.
--By Tom Skilling, WGN-TV Chief Meteorologist

Starting between 6 and 7 a.m. last Thursday morning and ending at noon yesterday, Chicagoans experienced 126 consecutive hours with below freezing temperatures. This caps off a cold start to December that has seen temperatures average 4 to 5° below normal over a good portion of central and northern Illinois. A warm-up has started that should peak with highs in the 40s Friday and Saturday and even nighttime lows Thursday and Friday staying above freezing. These warmer readings along with light rain or drizzle Friday and Saturday could see much of the snow cover over NE Illinois vanish. However, low pressure moving out of the southern plains is forecast to track through northern Illinois Saturday. This could produce new snow accumulations later Saturday night. An arctic high pressure air mass will surge into the Midwest Sunday with Chicago’s afternoon temps probably falling into the teens.
-By Paul Dailey, WGN Weather Center Meteorologist

There's not been this much snow on the ground in the city since last February. The 8" cover of snow at Midway Airport Monday marks only the third time a Dec. 17 since 1928 has featured snow as deep.

A shallow layer of cold air a little over 500 feet deep hugs the area snowpack as Tuesday dawns. This has forced gusty southerly winds several hundred feet off the ground and allowed some areas of fog to form. It has also set up an interesting situation in which the tops of some of Chicago's tallest skyscrapers are in "warmer" air than at street level. With daytime heating, the strong winds will mix down to the surface and boost temps above 32º for the first time in a week.
A note on this past weekend’s snow of 10.1" at Midway Airport: Snows of such magnitude are infrequent. Of 1692 measurable snows on record at the site since 1928, only 34, just 2% of them, have reached or exceeded 10.1".

Jim Bayne sends us this great photo of the Sears Tower poking above
Monday morning's stratus and the day's inversion layer. Thanks Jim!

Photo courtesy of Jim Bayne

The same storm system that brought up to a foot of snow to portions of the Chicago area this weekend buried areas from northern Indiana and Michigan to New England with up to 15" of snow. Some of the heaviest totals included 15" at Walden, Vt., and Saranac Lake, N.Y., and 14" at Bronson, Mich., and Columbia City, Ind. (just northwest of Fort Wayne). Severe weather erupted on the storm's southern flank Saturday night, producing a swarm of tornadoes in southern Georgia that resulted in one fatality.
Warmer air will try to make inroads into Chicago this week, but the cold snow-covered ground here will not only retard the warm-up but also create a lot of low clouds and fog.
This week will start out on the cold and quiet side, but two storms are expected to affect this area -- one by midweek and the other next Saturday, raising the specter of more wintry precipitation for the fourth weekend in a row at Chicago.
--By Steve Kahn, WGN Weather Center Meteorologist

DECEMBER'S SECOND MAJOR SNOWSTORM PACKS A WALLOP

The weekend snowstorm is almost history. Skies have cleared from the Chicago area west while the last vestiges of lake-effect snow are exiting Porter County in northwest Indiana. The early stages of the storm arrived in waves beginning pre-dawn Saturday. The storm really got it's snow-act together Saturday evening as the low pressure system began to intensify as it moved up the Ohio Valley from western Kentucky to central Ohio.

At Midway, weather observer Frank Wachowski reported that snow fell at the rate of one inch per hour for eight consecutive hours beginning Saturday evening between 7-8 p.m. until 3 a.m. Sunday. The snow then began to taper off and ended there around 7 a.m. Frank's snowfall totaled 10.1 inches. This storm, the area's second major snow system this month, produced more snow than 3-8" totals the December 4-5 storm did.

At Arlington Heights snowfall was about 5 inches. The new snow lies atop an ice-crusted 4 inch
residual snowpack making the total snow depth here around 9 inches.

While the Chicago area is digging out, this storm is now spreading its arsenal of heavy snow and ice to the northeast where areas from the lower Great Lakes to New England are expecting more than a foot of snow. South of the heavy snow, the precipitation will transition to ice and then to rain.
Steve Kahn WGN Weather Center Meteorologist

As the weekend storm exits the Chicago area Sunday morning, heavy snow totals will be left in its wake. Tallies are likely to range from 5-9” northwest of the city to a foot or more in northwest Indiana.
The first half of December has been a rough one for Chicago, with frequent bouts of freezing precipitation repeatedly glazing the area. A major snowstorm on Dec. 4-5 brought up to 8” of snow to northern portions of the metropolitan area.
Not only has this December been snowy and icy, it has also been cold, averaging nearly 5º below normal. So far, there has been only one day this month with a high in the 40s, and the city recorded its earliest 0º reading in three decades on Dec. 6. More cold weather is on tap for tonight. As skies clear, the fresh snow cover will act as a cold-weather factory allowing readings to plunge into the single-digits with the coldest interior spots headed to near or even below zero.

--By Tom Skilling, WGN-TV Chief Meteorologist

2:35 p.m. Saturday Weather Update: Storm's snows overspreading into the area; increasing winds/blowing and drifting of heavy snow accumulations on the way

Weather conditions are deteriorating as the season's second major snowstorm begins affecting the Chicago area as of this 2:35 p.m. Saturday update. Visibilities in falling snow have plunged to 1/4 mile at some locations across our southern suburbs and are likely to vary between 1/4 and 3/4 mile over much of the metro area in the periods of heaviest snowfall, especially tonight into the first hours of Sunday morning. Rapid storm intensification continues to be predicted overnight by computer models as the storm center swings north into Indiana and northwest Ohio, putting us beneath the system's potent snow and wind-producing western flank. It's a track, given the anticipated added injection of lake moisture, which favors significant snow accumulations in the period between now and the opening hours of Sunday. Some overnight hours could see 1-2" fall per hour in the hardest-hit locations, though you shouldn't be surprised to see variations in snow intensities as the heavier snowfall arrives in waves. It continues to appear that snow amounts will vary across the area in the fashion laid out in our current forecast -- with far northwest suburban areas toward Rockford, Dixon and DeKalb likely to see something close to the 1-3" storm totals we've outlined (some spots there could be in line for 3-4" inches), the Fox Valley generally getting in on 5-7" while south suburban and some lakeside locations bear the brunt of this system with isolated accumulations as high as 10-12" not out of the question.

LAKE MOISTURE COULD ENHANCE SNOWFALL TOTALS
The wild card on final snow amounts, as is usually the case with storms like this, will be the degree of lake moisture which gets into this system. It's a factor expected to become a more and more important issue overnight as initially easterly winds early Saturday night back northeast then north into Sunday morning, increasing exposure to the lake surface and added moisture. Sunday's opening hours may well have snow still falling fairly heavily near Lake Michigan and in Indiana while lighter snows and flurries linger farther west before tapering off with ensuing clearing and falling temperatures (low 20s are likely by day's end). Snow amounts will trend lower the farther west and northwest of the city one travels -- especially in far western locations (i.e. west of the Fox Valley).

STRONG WINDS ALSO EXPECTED
Increasingly powerful winds are predicted to accompany the barometric pressure declines within the intensifying winter storm -- especially overnight and into Sunday -- raising the specter of blowing and drifting snow. Gusts of 20+ m.p.h. as the afternoon proceeds increase to 30+ m.p.h. at times by later Saturday night and Sunday morning. As always, open areas and roads which run perpendicular to the prevailing wind direction are likely to be subject to the most significant drifting.

All atmospheric evidence up to now continues to support our prediction of 4-8" in the city proper and its immediate suburbs with 8-10" totals likely in Chicago's southern suburbs and even some sections of Cook and Lake counties close to Lake Michigan into northern Indiana. The system itself is contributing 4-8" of these totals, and current expectations suggest 2-4" of lake snow in the storm's final 6-8 hours could be added to the tallies in counties adjacent to Lake Michigan in northeast Illinois as well as northern Indiana. That may lead to some localized 12" totals in Indiana in the hardest-hit locations.

SOME TECHNICAL FACTORS UNDERPINNING OUR CURRENT FORECAST
Temperatures at 38,000 feet are forecast by computer models to warm 12-degrees C Saturday night. Studies and experience has shown snowfall in inches at ground level usually averages about half that high-altitude temperature increase -- and that amount excludes much of the lake moisture which gets into the system. The Chicago area is also fast shifting into a region of varying upper air wind speeds -- what's known in the business as a zone of "speed shear" beneath the nose of an incoming jet stream wind speed maximum. This is an area in which air is lifted an cooled on a broad scale and explains the presence of the snow now sweeping into the area. So does evidence of warming which is on the increase at 5,000 feet -- indicating the system is entraining warmth and moisture necessary for snow production.

Raw computer model water-equivalent precipitation totals for this event have been pegged at between 0.40" and 0.80" by our most reliable computer models -- heaviest across Chicago's far southern suburbs, lightest far northwest and west. Figuring a 12 to 1 snow/water ratio -- the ultimate ratio will also be critical to how much fall ends up accumulating -- these water equivalent amounts would yield widespread 5-10" snowfalls. Days of monitoring as this system has approached have seen these computer precipitation numbers catch up with other snowfall forecast techniques employed as we generate expected snowfall totals. Consistency is a powerful indicator that this storm appears at present to be unfolding as indicated.

Of course, all these indications are one thing -- what nature ends up doing with them can be another. An unexpected jog in the track this storm follows, variations in snow/water ratios, and the accuracy of our models in predicting the atmosphere's evolution during this system can all affect the final results, and we will continue to monitor this system closely.

Hope this provides an indication of where we appear to be with this system, and that any travel should be done with extreme care until clouds break and the sun emerges from the diminishing overcast Sunday afternoon. When all things are considered, the storm is likely to reach its height in the overnight hours and, in areas near Lake Michigan eastward into Indiana, possibly keep the snow going at a good clip into the opening hours of Sunday -- even into Sunday afternoon in the north-central Indiana and Michigan snow belts.

--By Tom Skilling, WGN-TV Chief Meteorologist

Northern Indiana and Chicago's southern suburbs appear likely to become ground zero for the heaviest snows of this area's third consecutive weekend storm. The system, responsible for 8" of snow near Dodge City, Kan., and as much as 9" in eastern Colorado Friday, is in its developmental stages and could bring the city proper as much as 4-8" of snow. Totals are likely to drop off markedly the farther north and west one travels from the city.
Patches of light snow arrive Saturday morning and grow steadier by Saturday afternoon. But, Saturday night into early Sunday is expected to play host to the storm's most wintry combination of accumulating snow. Winds gust to 20 m.p.h. this afternoon and to 30 m.p.h.-plus Saturday night -- a situation which suggests blowing snow may become a problem in open areas. More snow may fall on some of these areas Saturday and Saturday night in this storm alone than the 8.7" which is considered the December norm.
--By Tom Skilling, WGN-TV Chief Meteorologist

Before 8.4" of wind-driven snow walloped Boston Thursday -- a record for Dec. 13 -- only 1.5" had fallen so far this season. But Boston's snowfall paled in comparison to other New England totals -- including 13" reported at Burrillville, R.I., and Whitman, Mass., and the 9.5" at Binghamton, N.Y. Thursday's storm may be only the opening salvo in a far more active pattern predicted across the region in coming weeks. A mammoth new coastal storm this weekend could bury interior New England under an even heavier layer of snow while blasting the huge coastal cities of the Mid-Atlantic and Northeast with heavy rain.
Chicagoans, who have suffered through December's opening 13 days with only 14 percent of the area's possible sunshine (39 percent is normal), are treated to precipitation-free weather Friday for only the second time this month. The day's predicted 28-degree high could end up the 3rd chilliest of the new cold season.
--By Tom Skilling, WGN-TV Chief Meteorologist

Travel east the next four days will be severely impacted by two low pressure systems forecast to move east up the Ohio Valley into New England, each producing significant winter weather. The forecast track of the storms appears to be just far enough south to give Chicago clouds and snowfall associated with the northern fringe of each storm, although Lake Michigan-aided snow enhancement in NE Illinois and NW Indiana could occur with Saturday’s storm.
Some areas of the Northeast are targeted for a double-barrel hit with heavy snow later today and then again Saturday and early Sunday. Portions of Pennsylvania, New York, Massachusetts, Connecticut, Rhode island, New Hampshire and Vermont appear set to absorb two 5 to 10”+ heavy snow events. Flooding could occur in Kentucky, West Virginia and southern Pennsylvania today with Ice storms also a threat in the latter two states.
--By Paul Dailey, WGN Weather Center Meteorologist

Cold air’s grip on the area has tightened. While small pockets of warm air at cloud level make it possible a little freezing drizzle could linger with Wednesday’s sporadic flurries, a repeat of Tuesday’s widespread 0.25” ice accumulations across most west and northwest suburban areas is unlikely. Tuesday’s 0.67” of precipitation (water equivalent) at O’Hare made it one of the city’s two heaviest precipitation events since the 1”+ deluge back on Aug. 23. With just 13% of it possible sunshine, December’s opening 11 days have been the cloudiest here since 1997.
As icy as it was over sections of the metro area Tuesday, areas west and north were hardest hit. By late Tuesday, 60,000 Iowa households were in the dark as a result of the icestorm there. Snow blanketed much of southern Wisconsin. Accumulations reached 7” at Cottage Grove just east of Madison while to the west of Milwaukee, Oconomowoc was hit by 5.9”.

-By Tom Skilling, WGN-TV Chief Meteorologist

Here’s Lorado Taft’s statue beneath a layer of ice at Lowden State Park. The statue picture here was photographed from Route 2 in Oregon, Illinois which is southwest of Rockford by Woody Mott. Our thanks to Woody and to Chief Meteorologist Eric Sorensen of Rockford’s WREX-TV Channel 13 for calling this photo to my attention. Eric reports that things are beginning to become icy again in the Rockford area now that 5pm temperatures there have dropped to 32 degrees.

Tom Skilling

Photo courtesy of Woody Mott of Oregon, Illinois

Our friend Anson Mount was good enough to send these shots taken around 8 a.m. Tuesday morning of ice in the Algonquin area. Many thanks, Anson!!

Tom Skilling

Temperatures inched above freezing for a time Tuesday—slowing if not halting altogether—the ice build-up in much of the Chicago metro area. Jeremy and Sarah share these shots of the ice Tuesday morning across the Lake in the Hills area. A wind shift to the northwest is introducing colder air, not only at the surface but at cloud level. It’s a development which is to allow rain to turn to “freezing rain”—a state in which it begins to turn to ice upon contact with a number of outdoor surfaces. As the cooling continues, mixed ice pellets or even some flakes of snow can’t be ruled out Tuesday night, though precipitation rates should be easing late tonight.

Thanks to Jeremy and Sarah for the great photos!

Tom Skilling

Serious ice accumulations, not unlike those which cut power to 410,000 Plains residents and snapped tree limbs across sections of 12 states Sunday and Monday, threaten sections of the Chicago area Tuesday. The region west and NW of the city—including the Fox Valley, DeKalb, McHenry and Boone counties and areas west toward Rockford and into southern Wisconsin appear at greatest risk for the heaviest ice build-ups. While temps gradually ease above freezing in Chicago and areas south, halting ice formation and the melting which has already occurred, readings may be hard pressed to break above freezing to the west.

Tuesday marks the fourth consecutive day this area has played hot to freezing rain or drizzle. An analysis of Chicago weather records dating back to 1924 by my colleagues Frank Wachowski and Steve Kahn reveals it’s something which hasn’t happened before.

--By Tom Skilling, WGN-TV Chief Meteorologist

More spectacular shots from ice storm-ravaged Oklahoma

Another of our former weather office interns Troy Christensen---who continues his meteorology studies at the University of Oklahoma---sends us these amazing photos of the horrific ice storm which has crippled sections of Oklahoma Sunday and Monday. Troy tells us:

" I just got my power back a couple of minutes ago, and I wanted to send you guys some pictures from the ice storm down here in Norman. According to the local electric company, more houses were without power today than at any time in history. Last night, it sounded like fireworks all over the place from snapping tree limbs and branches. We got about an inch or an inch and a half of ice."

Many thanks, Troy!

Tom Skilling

Photos by Troy Christensen

Former WGN intern Marty Eisses currently in Okahoma sent along this fantastic picture of the Oklahoma City landscape during the current ice storm which began there on Saturday night.

Marty tells us that.. Freezing rain began Saturday night. As of Sunday, 1030 p.m. there is about 1/4-3/16 of an inch on the cars and tree branches. I can see many blue flashes lighting up the sky as transformers are blowing. The National Weather Service there is forecasting about 0.3-0.8 of an inch of ice thru Tuesday

Photo by Marty Eisses

Brent Gilles, who interned with us a year ago and now works in Norman, Oklahoma, forwards us these amazing pictures of the icestorm which has decimated sections of that state. Brent reports his power out and says he can’t leave his apartment complex because downed trees have blocked his exit. Stay safe Brent—and many thanks for the update!

Tom Skilling

A persistent upper-level jet stream pattern flowing from the Southwest to northern New England has allowed a series of low pressure systems to develop in the southern Rockies and Texas Panhandle and move northeast through the Ohio Valley to the East Coast. This pattern is expected to continue into midweek, with two more low pressure surges forecast to impact northern Illinois Tuesday and Thursday. Water-equivalent precipitation with the late Monday night/Tuesday storm could be as much as a half to one inch, so surface temperatures now forecast to warm slightly above freezing will be crucial as to whether northeast Illinois will receive rain or freezing rain.
The following storm looks like it will lean more to the cold side with a rain/wet snow combination beginning later Wednesday. The upper-air pattern will then shift northwest-southeast over Chicago, and a cold Canadian air mass will be steered into the western Great Lakes late in the week.
--By Paul Dailey, WGN Weather Center Meteorologist

Saturday evening numerous accidents were reported on I-80 and areas to the south as freezing rain and freezing drizzle created hazardous conditions on roads as well as streets and sidewalks. With the 20,000-foot steering level winds flowing from the SW to NE, low pressure originating in the Texas Panhandle tracked east up the Ohio Valley, spreading a wintry mix of snow, sleet and cold rain or freezing rain from Missouri into into central and northern Illinois and northern Indiana. No sooner does this sytem’s cloud shield move east than a second look-alike low pressure system is forecast to take a similar track Tuesday and Wednesday. Early indications are this midweek storm might entrain slightly warmer air producing a period of rain in Chicago Wednesday before changing back to possible accumulating wet snow that night. A bitterly cold Canadian air mass is then expected to spread east over the Great Lakes and Midwest.
--By Paul Dailey, WGN Weather Center Meteorologist

It's been a wild opening week for Chicago's meteorological winter 2007-08.
It started with last weekend's icy glaze, followed by the midweek snowstorm and the city's earliest 0-degree reading since the 1970s. And now, the city is facing two more winter storms that threaten a return of adverse weather, first this weekend and then again by the middle of next week.
Latest computer forecast trends hint at an icy mix for most of the city this weekend with more snow to the north and glaze to the south.
Following a brief respite Monday and early Tuesday, the second storm is expected to roll in, once again bringing a threat of rain and/or snow to the city. Very cold air currently building across the northern Plains and southern Canada is forecast to plunge south into the Midwest in the wake of this storm, bringing another round of early season cold by the end of the week.
--By Steve Kahn, WGN Weather Center Meteorologist

Not since 1976—a period of more than three decades—has Chicago’s official temperature dropped to 0° so early in a cold season. For five minutes beginning at 4:04 a.m. Thursday morning, Chicago’s official temperature bottomed out at 0°—a reading which tied the 1972 record for December 6. The frigid benchmark isn’t typically reached here for another three weeks and didn’t occur for another two months a year ago. The first 0° waited until a -6° low was recorded Feb. 3 earlier this year. The combination of clear skies, dry air, a fresh snow cover and light winds was behind the sub-zero readings which occurred at a number of west and NW suburban locations early Thursday.
The week’s third snow, part of a system which left up to 4.5” on the ground in Iowa, arrived in a weakening state Thursday evening. The 3-5 hour snowfall was predicted to deposit 1-2” in the Chicago and end well before sun-up Friday.
--By Tom Skilling, WGN-TV Chief Meteorologist

From Winter in northern Wisconsin come these photos from our friend and regular photo contributor Dan Hanson. The North Woods of Wisconsin has seen snow nearly every day recently, Dan reports, and the flakes coming down today are big. He reports Winter’s snow accumulation from the latest system is 8”. Thanks for the update Dan, and stay warm!

Tom Skilling

Photos courtesy Dan Hanson, Winter, Wisconsin

Wednesday’s 2-9” area snowfall hasn’t settled and another 2-4” is on the way. It’s part of an extraordinarily active pattern which may result in three additional winter disturbances over the coming week. The first arrives with snow toward nightfall in the Fox Valley then spreads into the city proper an hour either side of 6 p.m. The bulk of this system’s snow appears likely to fall in just 6-8 hours, diminishing in Friday’s predawn hours.
Bursts of lake snow Wednesday sent storm tallies to more than 9” Wednesday. Buffalo Grove’s 9.2” was the area’s heaviest followed closely by Lincolnshire’s 9.0”. Both Waukegan and Arlington Heights logged 8” while city snowfalls included 5.5” at O’Hare and 4.6” at Midway. Amounts tapered to 2” in Kankakee County’s Bonfield.
A 3” or greater snowfall Thursday night would mark only the third time since 1884 that December’s opening week has hosted two 3”+ snows.

--By Tom Skilling, WGN-TV Chief Meteorologist

Elizabeth Stock shares these shots of snow-covered Belmont Harbor with us in the wake of Tuesday night/Wednesday’s 3-9” area snowfall. Thanks Elizabeth!

-Tom Skilling

This was the scene at 10:30 a.m. Wednesday morning as lake snow invaded the Waukegan area. In typical fashion, bursts of lake snow from Milwaukee south to Chicago slashed visibilities at times to a half mile. This photograph from Waukegan Airport comes to us from pilot Anson Mount. Many thanks Anson!

Tom Skilling

Photo courtesy of Anson A. Mount Ill.

Bette Morrow of Mokena shares this shot of Tuesday night’s snow with us. Thanks Bette!

Tom Skilling

2:30 PM Wednesday Update

Coldest night of the season to follows the equivalent of a full December’s snow in parts of the area; more snow due Thursday night and icy storm threatens by Sunday

Single digits low temperatures, the coldest to date this season, are headed for many sections of the Chicago area Wednesday night. Freshly-fallen snow is among the most reflective surfaces on earth—something which facilitates strong cooling once the sun sets. With the area now solidly snow covered, Wednesday night/Thursday morning lows of 0 to 5-degrees in the coldest western suburbs aren’t out of the question ranging to the low teens overnight in northwest Indiana and up against Lake Michigan in the city. The cold air’s arrival is already underway. Temperatures as we post this at 2pm continue falling and have dropped to the low 20s across Chicago western suburbs.

The final moderate bursts of lake snow continue riding most directly into Cook and Will counties in Illinois and Lake and Porter counties in Indiana but are shifting south with time and expected to be exiting Cook County entirely later this afternoon. The plume of lake moisture is on the move, drifting south into Indiana where it will diminish tonight. Visibilities Wednesday morning and early afternoon have dropped under a mile in spots during the heavier lake squalls---only to recover amid cloud breaks which allow sunshine. Skies have completely cleared in Chicago’s north and northwest suburbs.

These lake snows in combination with the more general “system” snow which fell late Tuesday and Tuesday night as the Alberta Clipper rushed by have pushed storm snowfall tallies to over 9” in areas just north of Chicago proper. That’s nearly a full month’s snowfall (based on area norms) in a single storm. Areawide accumulations range from 3 to 9.2”. And, we’re not done yet. The pattern remains extraordinarily active and more accumulating snow is due Thursday night followed by what could be another icy weekend storm Saturday night and Sunday---the second is as many weekends!

Here’s a brief rundown of some area snowfalls which my CLTV colleague Mike Hamernik helped put together. Many thanks to veteran National Weather Service observer Frank Wachowski and to my meteorological colleagues Steve Kahn and Richard Koeneman as well as to NWS-COOP observers Phil Rider in Mundelein and Patrick Skatch in Oak Brook among others as well as to the National Weather Service Forecast Office at Romeoville and all who have contributed snow observations:

Buffalo Grove 9.2”

Lincolnshire 9.0”

Waukegan 8.0”

Arlington Heights 8.0”

Mundelein 7.6”

O’Hare 5.5”

Oak Brook 5.4”

Downers Grove 5.4”

Midway Airport 4.6”

Valparaiso 4.4”

Park Forest 4.0”

Wilmington 3.0”

Morris 2.8”

I’ll update the situation on our 5:55 pm and 9 PM WGN reports and here on our weather blog. Until then, be safe!

Tom Skilling

Chief Meteorologist WGN/Chicago Tribune

Well, the Alberta Clipper really did a number in the Arlington Heights area. Snowfall as of 6 a.m. this morning totaled 7 inches. The snow began Tuesday afternoon around 3 p.m. but was quite light until about 6 p.m. By mid evening 2.5" had fallen, but it was still snowing steadily and the snow continued overnight, obviously picking up in intensity. Only a few flurries are falling at 7:40 a.m. but radar indicates that some lake effect could move in later this morning.

The area’s heaviest snowfall of the season isn’t over yet. While the current storm’s large scale “system-wide” snow moves on Wednesday, its “lake-effect” phase is just beginning. Alberta Clippers on tracks as far south as today’s are notorious for tapping lake moisture in their final hours over the Chicago area. Easterly winds, which travel over only 75 miles of water, shift more north-northeast Wednesday morning as the storm’s center races southeastward out of central Illinois. This more than triples the distance over water before rushing ashore. That plus the arrival of colder air on the system’s backside produces an environment in which lake-effect snow bands flourish. Though hardly steady snow-producers, snow can arrive in visibility-reducing bursts capable of a couple of fast inches of snow. Final area snowfalls are likely to wind up in the 3-6” range with a few 7-8 inch totals possible at any location hit by some of the lake snow showers.

Southeastbound snow is moving into northern Illinois; visibilities down to to 1/4 to 3/4 mile in snow over western Wisconsin and Minnesota; due to start in Chicago 4-5 p.m.

The season’s biggest snow to date is just hours from Chicago. The axis of the heaviest snowfall is expected to set up across the entire Chicago area generating 3-4” totals in areas well west and southwest of the city while the length of the period in which lake moisture is tapped Wednesday morning and early afternoon will determine just how much additional accumulation occurs in lakeside counties of northeast Illinois. Our forecast currently puts this amount around 5-6” — but locally higher totals aren’t completely out of the question in some lakeside locations given the possibility lake-effect snows, which could linger at times into early afternoon Wednesday, prove more active than currently predicted. Given the warmth of the lake and the vigorous temperature decline with height, it’s a possibility which shouldn’t be ignored. Just how much lake moisture ultimately becomes entrained in the snow system as winds back NE toward morning and NNE on its backside during Wednesday remains the largest snow accumulation wildcard with the current system. As wind become more NW mid and late Wednesday afternoon, it’s likely any lake-effect snowfall will shift into northwest Indiana.

Forecasters employ many techniques when predicting snow. A range of raw computer model precipitation projections are screened. In addition, the rate of cooling predicted at the 700 mb level (roughly 10,000 ft.) is examined on what meteorologists refer to as the “magic” chart — and so is the rate at which temperatures are warming above ground at the 200 mb. Believe it or not, there’s a relationship between warming at that level and how much snow falls down here at ground level. Also examined is the predicted water content through a swath of the lower atmosphere — the so-called “mixing ratio”. And another technique, developed by the late Al Morrison of the National Weather Service which relates the predicted speed at which upper air impulses move and the intensity of these impulses. Such an examination offers valuable guidance on the type of accumulation a given storm may produce. The differing techniques suggest 3-6” is a good estimate on potential accumulation.

Radar indicates the southeastbound area of snow associated with today’s approaching Alberta Clipper has entered northern Illinois and is streaming at cloud level into Chicago’s northwest suburbs within the past hour. Flurries may precede this storm’s primary precipitation. But its steady snow is to begin over the city between 4-5 p.m. -- earliest in northwest McHenry, Lake and Boone counties — and closer to 6-7 p.m. in far southeast suburbs.

We’ve been monitoring Wisconsin and Minnesota WeatherBug cameras and can report to you that the snow has overspread Madison, Wisconsin and is noticeably impacting visibilities there. But, the real visibility reduction is occurring just to the northwest of Madison as we file this update around 2:30 pm Tuesday afternoon. Weather observations in that region since late morning indicate visibilities have dwindled to 1/2 mile in snow from sections of western Wisconsin near LaCrosse northwestward across the Twin Cities and all the way to Brainerd in northern Minnesota. Far and away, the heaviest snowfall is occurring in the Minneapolis area where moderate snow and 1/4 mile visibilities have been reported. Reports at Midday indicated 3-5” of snow was down in northern Minnesota and eastern North Dakota, the source region of Chicago’s coming snow. 5 to 10” are predicted in the Duluth area, enhanced by moisture off Lake Superior and the cold temperatures at which the snow is falling.

The area has certainly encountered worse December snows than the one on the way. But not since the 8.8” snowfall on February 13 earlier this year has the Chicago area received more snow than the totals predicted with the incoming system.

A new round of accumulating snow is due Thursday night into early Friday and a mix of wintry precipitation is to occur Saturday night into Sunday. There are also hints a fourth precipitation system could be headed this way next Tuesday. Current temperature projections suggest the rain/snow line may not reside far from Chicago.

Tom Skilling
WGN-TV Chief Meteorologist

The biggest snow of the new season appears to be on the way—potentially the biggest since 8.8” fell earlier this year on Feb. 13. A classic Alberta Clipper, named for the southwest Canadian province through which the storm passes before diving into the Midwest, is responsible for the impending snowfall. An offshoot of a powerhouse Pacific storm which lambasted the Pacific Northwest Monday, the system boasted a central pressure (949 mb. or 28.02”) Sunday night—the equivalent of a Category 3 hurricane.
Near Lake Michigan, flurries may flutter to earth sporadically into early afternoon. But, snow begins falling more steadily from Tuesday afternoon’s thickening overcast, and is likely to fall heaviest at times toward evening and through a good portion of the night. Initially light winds strengthen Tuesday night and gusty NNE winds deliver lake-effect snow showers Wednesday. Snowfalls in the 3-6” range appear a good bet.
--By Tom Skilling, WGN-TV Chief Meteorologist

Winter’s underway big time in Michigan’s Upper Peninsula. My friend and meteorological colleague John Dee, who lives on Michigan’s Keweenaw Peninsula—the “finger” of land on the U.P. into Lake Superior and often receives phenomenal amounts of winter snow, e-mailed the following report I thought you might find interesting:

“Since last Thursday (Nov 27th), I have picked up 39 1/2" of snow at my house and have 24" on the ground. The kick off to all of this happened last Tuesday in white out conditions caused by 4" of snow in 1 hour combined with 71 mph winds! I have never seen it snow and blow so hard at the same time. I know seasonal forecasting is like throwing a dart at a wall, but looking back, there is some historical connection between mild autumns up here and an abrupt change to winter late in November leading to a cold and snowy winter for these parts. I have also noticed that the Keweenaw can many times be the "canary in the coal mine" for the rest of the Midwest. Meaning if we start out our winter cold and snowy it can foretell the same for not just us, but much of the northern 1/2 of the Midwest for the rest of the winter.”

Interesting observations and a great photo of the snow up your way over the weekend, John! Many thanks!

-Tom Skilling

Photo courtesy: John Dee

Jay Kleeman shares these photographs of this past weekend’s storm. The system ended up producing 0.86” water equivalent precipitation, of which 1.2” fell as snow—even as the vast majority of the storm’s moisture fell as supercooled liquid (freezing rain), coating all outdoor objects with ice. Many thanks to Jay for sharing these shots of the storm with us! Now we prepare for snow—expected to blow off the lake as flurries Tuesday then build to steadier “system” snow Tuesday night and, finally, to incorporate some lake moisture Wednesday. The area should take on a snow-covered winter wonderland appearance Tuesday night and Wednesday!

Tom Skilling
Chief Meteorologist

Photo courtesy: Jay Kleeman

Winter got off to an auspicious start Saturday as Chicago was battered by a smorgasbord of weather that included snow, sleet and freezing rain. While the storm brought mainly glaze and rain to the Chicago area, the Upper Midwest was buried in snow. Babbitt, located in the Minnesota Arrowhead, received 13", while Bayfield and Niagara in far northern Wisconsin both logged 10".
Brief warming Sunday morning removed most traces of this winter's first shot, but the week ahead will likely bring one and possibly two chances for snowfall to this area. A storm system originating in Alberta will race southeast through the area Tuesday night and Wednesday, bringing a period of accumulating snow. A surge of cold air will follow, setting the stage for a second storm currently projected on a path from the southern Plains up the Ohio Valley Thursday night and Friday. This track is one of the most favorable for a significant snowfall in Chicago.
--By Steve Kahn, WGN Weather Center Meteorologist

Scattered power outages hit portions of northeast Illinois Saturday as the first major winter storm of the season brought about 0.5”-1.5” of snow followed by several hours of glazing freezing rain and sleet. Midway and O’Hare both received about 0.5” of snow with heavier totals approaching 2” in the Wisconsin border counties.
Strong south winds slowly boosted temperatures above the freezing mark Saturday night starting a melting process that will rev into high gear Sunday as temperatures surge to near 50º. The warmth will be short-lived though, as temperatures plummet late Sunday and Sunday night as strong northwest winds bring in much colder air in the storm’s wake.
While Illinois escaped most of the storm’s snow, Wisconsin did not. Green Bay, coming off its driest November on record since 1886 with only .10” of precipitation was expecting up to 8” of snow.
--By Steve Kahn, WGN Weather Center Meteorologist

The bad news is that light freezing rain is continuing across much of the Chicago metropolitan area this evening, but the good news is that temperatures are creeping toward 32 degrees. At 7 p.m. both O'Hare and Midway had reached 30 degrees with 31 degrees readings reported at DuPage, Wheeling and Aurora. Thawing has already begun at Kankakee where the mercury stands at 34 degrees.

The temperature will continue its slow rise through the night reaching the 40s on Sunday. This will allow today's snow and glaze to melt away. High temperatures will likely approach the 50 degree mark Sunday afternoon, but readings will crash back into the 30s by evening as strong northwest winds sweep in a shot of colder air. By Monday morning, the mercury should hover near 20 degrees.

With the city's first winter storm of the season about to become history, forecasters are already looking at the next system which may be approaching the area by late Tuesday. This storm, an Alberta Clipper type, could bring a round of accumulating snow to the city Tuesday night into Wednesday. In tune with the turn of the calendar to December 1, meteorological winter has truly arrived in Chicago.

Steve Kahn WGN Weather Center Meteorologist

A GUIDE TO FORECASTING AND UNDERSTANDING THE DIFFERENT TYPES OF WINTER PRECIPITATION

Today's winter storm brought a variety of winter precipitation to the Chicago area with snow, sleet and freezing rain all occurring. Tonight as surface temperatures rise above 32º, rain will fall. This graphic that originally appeared on the Chicago Tribune weather page on January 3, 2005 helps explain what kind of vertical temperature profile in the lower 2 miles of the atmosphere is needed to produce the various types of winter precipitation.

2:45 P.M.Update: Switch to freezing rain sweeping the area, icing problems to grow before temps break above freezing later this evening

Freezing rain and ice pellets are fast becoming the favored precipitation mode Saturday afternoon. Early snow has been replaced by freezing rain in Chicago, as well as at DuPage, Aurora and Rockford, signaling the fact that powerful 60+ mph southerly winds several thousand feet above the surface are warming the air there quickly. Roads conditions are icy and challenging--especially less traveled thoroughfares, sidewalks and driveways.

Strong warming aloft is shutting down the brief interval of crystal formation in the clouds which fueled this storm's early snowflake development. The result is ice pellets (sleet)----but even more prevelantly super-cooled freezing rain---rain which falls as liquid but at a temperature below freezing, a state in which it freezes upon contact with cold outdoor surfaces---are to dominate the next 6 hours until temperatures at the surface surge above freezing later Saturday night. Computer models indicate as much as 0.75" of the storm's total 1"+ tally may fall during this interval of sub-freezing temperatures producing significant ice accumulations. Readings will break above freezing later tonight ultimately allowing this ice to melt. The prospect that temperatures will flirt with 50-degrees before crashing behind a cold front later Sunday the period in which icing is to be a major problem is to occur from now through around 9-11 pm Saturday night.

The storm's brief spell of snow has led to accumulations of 0.5" at Midway and 1" at O'Hare as of this 2:45 pm filing. Observer Phil Rider at Mundelein reported .9" followed by a change to sleet, and here at WGN snowfall totaled about 3/4" before turning to sleet and freezing rain.

Freezing rain is now coating colder outdoor surfaces. The weight of this ice and the gusty winds accompanying it increase the risk that tree limbs and even some power lines may come down in portions of the metro area.

Further updates will appear here during the course of the storm. Be safe!

Tom Skilling WGN-TV Chief Meteorologist
Steve Kahn WGN-TV Weather Center Meteorologist

WINTER STORM UPDATE

ICY CONDITIONS EXPECTED TO DEVELOP THIS AFTERNOON AND EVENING ESPECIALLY IN AREAS NORTH AND WEST OF THE CITY

Cloudiness has been thickening and lowering across the Chicago area this morning as the winter storm approaches. Temperatures have also been on the increase, rising into the middle and upper 20s by mid-morning. However dew points remain low, ranging from the single digits to the teens across the metropolitan area.

Radar returns are increasing as a strong southwesterly flow brings a slug of moisture into the area, but due to the initial dryness of the atmosphere it will take several more hours for it to moisten to saturation and allow the precipitation forming in the clouds to reach the ground.

Morning upper-air reports show warm air moving in aloft, so the precipitation here is likely to fall as sleet and freezing rain instead of snow. At the 5,000-foot level, temperatures are already near or above freezing with the warming continuing, Preciptation has begun in Iowa and Missouri with most locations reporting sleet and/or freezing rain.

We expect precpitation to move into the Chicago area from the southwest during the afternoon. There may be a brief flurry of snow at the onset, but that should quickly transition into sleet and freezing rain.

The most critical time for icing conditions should be from about 3 to 9 p.m. Temperatures should continue to rise slowly, though readings may drop back a few degrees when preciptation begins due to cooling from evaporation. Areas in the city and close to the lake should experience the least amount of icing as warmer air moves in from Lake Michigan with the most serious icing expected west and north of the city.

Readings should climb above freezing early tonight, allowing the the ice and glaze to melt. By Sunday temperatures could be approaching the 50-degree mark. Temperatures will crash in the storm's wake Sunday afternoon with a period of snow flurries expected.

Updates will be posted as necessary this afternoon and evening.

--By Steve Kahn, WGN-TV Weather Center Meteorologist