A well warranted Winter Storm Warning remains in effect for the entire Chicago area. In addition, the National Weather Service has issued a Blizzard Watch for some southern suburbs. For updated snowfall totals and the latest on the Blizzard Watch, follow the link below to the WGN Severe Weather Blog
WGN Weather Center Blog
WGN-TV Chief Meteorologist Tom Skilling and the WGN Weather Center staff provide daily coverage of weather in the Chicago area.
A February snowfall of 10" or more occurs on average only once every 16 years in Chicago. Only five such storms are on the books at Midway Airport in the 81 years since 1929. Tuesday's storm may well become the sixth! Before it finishes with the Chicago area, 8 to 14 inches of snow may accumulate--the season's heaviest to date and the biggest storm to occur here since nearly a foot fell here over two days just over a year ago in late January
The current system's impact on the Chicago area is only in its early stages as Tuesday gets underway. Three rush hours may ultimately be impacted by the system--none more than Tuesday evening's when snowfall will be at its height and winds will be gusting to 25 mph--strong enough to begin sending the additional 4 to 7" of snow predicted to fall Tuesday airborne in some open areas surrounding the city. That's also the period in which an infusion of lake moisture is to begin, supplementing snowfall. Lake enhancement of snowfall could end up spanning 10-14 hours, extending into the opening hours of Wednesday morning even as non-lake-effect snow tapers to passing flurries at inland locations. It's an important reason this storm's heaviest snow totals are predicted to occur in lakeside counties of Illinois, Wisconsin and Indiana.
Explosive intensification of the storm is predicted by computer models later Tuesday as a secondary center forms off the mid-Atlantic Coast. Storms intensify when air rushes aloft at increasing speed. Ground-level winds strengthen as part of this intensification process. The rate at which air ascends increases, encouraging air to rush in from the storm's periphery at faster speeds to replace the upwelling of air at the heart of the storm.
The impact of the current storm's intensification across the Chicago area could become most noteworthy Tuesday night when winds approach their peak, gusting as high as 30 to 40 mph, particularly in areas surrounding the city. Winds of that strength should easily lift snow and hurl it through the air, producing near-blizzard or blizzard conditions. A blizzard is defined by the National Weather Service as three or more hours with winds gusting to or above 35 mph, and during which blowing snow reduces visibilities to a quarter mile or less. The density of structures such as homes and buildings in the city and close-in suburbs often generates enough drag on the moving air to subdue velocities there. But this doesn't happen in open areas surrounding the city, and these areas appear particularly vulnerable to potentially significant blowing and drifting snow Tuesday night.
Latest storm producing 1,300-mile corridor of snow; "Bosnywash" corridor being hit hard again
As unbelievable as it may seem, the Nation's Capital--where a snowfall of 1 to 3" can cause serious travel problems--is under the meteorological gun once again. Just three days from one of the region's worst blizzards in history, forecasters are predicting 10 to 20 inches of new snow may fall as winds strengthen later Tuesday. This promises a rash of new travel problems.
The current system's impact on the Chicago area is only in its early stages as Tuesday gets underway. Three rush hours may ultimately be impacted by the system--none more than Tuesday evening's when snowfall will be at its height and winds will be gusting to 25 mph--strong enough to begin sending the additional 4 to 7" of snow predicted to fall Tuesday airborne in some open areas surrounding the city. That's also the period in which an infusion of lake moisture is to begin, supplementing snowfall. Lake enhancement of snowfall could end up spanning 10-14 hours, extending into the opening hours of Wednesday morning even as non-lake-effect snow tapers to passing flurries at inland locations. It's an important reason this storm's heaviest snow totals are predicted to occur in lakeside counties of Illinois, Wisconsin and Indiana.
Explosive intensification of the storm is predicted by computer models later Tuesday as a secondary center forms off the mid-Atlantic Coast. Storms intensify when air rushes aloft at increasing speed. Ground-level winds strengthen as part of this intensification process. The rate at which air ascends increases, encouraging air to rush in from the storm's periphery at faster speeds to replace the upwelling of air at the heart of the storm.
The impact of the current storm's intensification across the Chicago area could become most noteworthy Tuesday night when winds approach their peak, gusting as high as 30 to 40 mph, particularly in areas surrounding the city. Winds of that strength should easily lift snow and hurl it through the air, producing near-blizzard or blizzard conditions. A blizzard is defined by the National Weather Service as three or more hours with winds gusting to or above 35 mph, and during which blowing snow reduces visibilities to a quarter mile or less. The density of structures such as homes and buildings in the city and close-in suburbs often generates enough drag on the moving air to subdue velocities there. But this doesn't happen in open areas surrounding the city, and these areas appear particularly vulnerable to potentially significant blowing and drifting snow Tuesday night.
Latest storm producing 1,300-mile corridor of snow; "Bosnywash" corridor being hit hard again
As unbelievable as it may seem, the Nation's Capital--where a snowfall of 1 to 3" can cause serious travel problems--is under the meteorological gun once again. Just three days from one of the region's worst blizzards in history, forecasters are predicting 10 to 20 inches of new snow may fall as winds strengthen later Tuesday. This promises a rash of new travel problems.
Dear Tom,
What do the lines on weather maps mean?
--Jenna Jamieson (5th grade), Bloomingdale, Ill.
Dear Jenna,
Meteorologists use weather maps to display information such as temperatures, air pressure and winds over large areas. The maps give forecasters the ability to see the big weather picture and, at a glance, to understand "what's going on" with the weather. That information is the starting point in the preparation of weather forecasts. Many different lines are drawn on weather maps, but the most common ones are called "fronts." Fronts show the boundaries between different kinds of air masses (such as hot and cold, or humid and dry). Lines called isobars frequently appear on weather maps as well. Isobars connect locations that have the same air pressure, and they show where the air pressure is low (usually with stormy weather) or high (usually with fair weather).
What do the lines on weather maps mean?
--Jenna Jamieson (5th grade), Bloomingdale, Ill.
Dear Jenna,
Meteorologists use weather maps to display information such as temperatures, air pressure and winds over large areas. The maps give forecasters the ability to see the big weather picture and, at a glance, to understand "what's going on" with the weather. That information is the starting point in the preparation of weather forecasts. Many different lines are drawn on weather maps, but the most common ones are called "fronts." Fronts show the boundaries between different kinds of air masses (such as hot and cold, or humid and dry). Lines called isobars frequently appear on weather maps as well. Isobars connect locations that have the same air pressure, and they show where the air pressure is low (usually with stormy weather) or high (usually with fair weather).
The entire Chicago metropolitan area is being placed under a winter storm warning effective from this evening through noon on Wednesday. Previous the winter storm warning had been in effect only for counties close to Lake Michigan where lake-enhanced snowfall was expected to boost snowfall total and surrounding areas were under a winter weather advisory. The warning area was expanded because strong winds are expected to develop gusting to 35-40 mph. The high winds will cause much blowing and drifting of the newly fallen snow creating very hazardous conditions that could result in near blizzard conditions in open areas.
Chicago area counties now included in the Winter Storm Warning include..
In Illinois
Cook, DuPage, Lake, IL, McHenry, Kane, Will, Boone, Winnebago, Ogle, Lee, DeKalb, Kendall, La Salle, Grundy, Kankakee, Livingston, Ford and Iroquois
In Indiana
Lake, Porter, Jasper, Newton
The sunshine with which Monday afternoon has opened belies the area's meteorological fate in coming days. The Chicago area sits at the precipice of a major snow event which may prove the heaviest and lengthiest of the 2009-10 season. To date, the 7.5" which fell Jan 6-8 tops this season's snowfall charts. The system which looms appears capable of producing 8 to 14" accumulations, heaviest in counties adjoining Lake Michigan from northeast Illinois into southeast Wisconsin and northwest Indiana, in what could be a 35 to 40 hour snowfall. A snowfall of nearly a foot would be the heaviest here in over a year, according to our climate guru Frank Wachowski. A 35-40 hour stretch is a VERY LENGTHY period of snowfall by Chicago standards which could impact 2 and possibly 3 rush hours Tuesday into Wednesday morning!
We understand a great deal more about snowflake formation than we once did--and this understanding is crucial when it comes to making accumulation forecasts. Here's why. Because the condensation nucleii--the tiny particles which float in the air around which snowflakes form are primarily composed of clay in this region of the world--this makes it critical for there to be to layer of air with a temperature of-12 to -14-degree C or colder in order to initiate snow crystal formation around the clay nucleii which predominate in the Midwest. (Were these particles composed of substances other than clay, that would change the temps required to form crystals to something other -12 to -14 deg C). The deeper and colder that cold layer is in a storm, the more efficient snowflake formation is and the more "fluff" which occurs in the snowflakes which form. This storm will have a comparatively DEEP cold layer--so fluffier snowflakes seem a good bet.
One of the truly useful tools forecasters today have available are computer model estimates, based on analysis of the depth and temperature of the layer of cold air in snow situations as well as the predicted winds (strong winds can limit snowflake size by bumping flakes together and crushing the crystals at the edge of flakes), of what's called the "snow-water" ratio--in other words, a calculation of how much snow is likely to develop from the water a storm is expected to take out of the atmosphere.
The incoming storm is predicted to produce a 16.3 to 1 snow/water ratio. (The typical storm here produces ratios closer to 10 to 12 to 1.) That means that given the size of snowflakes predicted in this storm, 16.3" of snow would result from an inch of water. A suite of computer models storm suggest the storm which hits in coming days will generate 0.45" to 0.80" of water. Using the 16.3 to 1 snow/water ratio, this suggests 8 to 14" of snow may occur by Wednesday morning. The winds forecast with this storm will be modest Monday night but will increase markedly Tuesday and Tuesday night. Gusts to 25 to 35 mph are not out of the question later Tuesday night and Wednesday morning--more than enough to encourage blowing and drifting.
We expect snow to overspread the area this evening and to be falling steadily areawide by midnight--then to continue heavy at times Tuesday and much of Tuesday night. Lake effect snow could spill over into Wednesday morning and presents one of the wildcards of this storm situation-namely, how much lake moisture is to be entrained in this storm. The presence of lake moisture in the snowfall equation with the new storm makes it most likely the heaviest snow totals by the time the storm winds down Wednesday morning are to occur in lakeside counties from Kenosha County WI south to Lake and Cook Counties Illinois into Lake, Porter and La Porte Counties IN.
We plan to keep the updates coming here at wgntv.com on our Severe Weather Blog as well as on our reports over WGN TV and radio. Stay safe and thanks for checking out our blog!
Tom Skilling
We understand a great deal more about snowflake formation than we once did--and this understanding is crucial when it comes to making accumulation forecasts. Here's why. Because the condensation nucleii--the tiny particles which float in the air around which snowflakes form are primarily composed of clay in this region of the world--this makes it critical for there to be to layer of air with a temperature of-12 to -14-degree C or colder in order to initiate snow crystal formation around the clay nucleii which predominate in the Midwest. (Were these particles composed of substances other than clay, that would change the temps required to form crystals to something other -12 to -14 deg C). The deeper and colder that cold layer is in a storm, the more efficient snowflake formation is and the more "fluff" which occurs in the snowflakes which form. This storm will have a comparatively DEEP cold layer--so fluffier snowflakes seem a good bet.
One of the truly useful tools forecasters today have available are computer model estimates, based on analysis of the depth and temperature of the layer of cold air in snow situations as well as the predicted winds (strong winds can limit snowflake size by bumping flakes together and crushing the crystals at the edge of flakes), of what's called the "snow-water" ratio--in other words, a calculation of how much snow is likely to develop from the water a storm is expected to take out of the atmosphere.
The incoming storm is predicted to produce a 16.3 to 1 snow/water ratio. (The typical storm here produces ratios closer to 10 to 12 to 1.) That means that given the size of snowflakes predicted in this storm, 16.3" of snow would result from an inch of water. A suite of computer models storm suggest the storm which hits in coming days will generate 0.45" to 0.80" of water. Using the 16.3 to 1 snow/water ratio, this suggests 8 to 14" of snow may occur by Wednesday morning. The winds forecast with this storm will be modest Monday night but will increase markedly Tuesday and Tuesday night. Gusts to 25 to 35 mph are not out of the question later Tuesday night and Wednesday morning--more than enough to encourage blowing and drifting.
We expect snow to overspread the area this evening and to be falling steadily areawide by midnight--then to continue heavy at times Tuesday and much of Tuesday night. Lake effect snow could spill over into Wednesday morning and presents one of the wildcards of this storm situation-namely, how much lake moisture is to be entrained in this storm. The presence of lake moisture in the snowfall equation with the new storm makes it most likely the heaviest snow totals by the time the storm winds down Wednesday morning are to occur in lakeside counties from Kenosha County WI south to Lake and Cook Counties Illinois into Lake, Porter and La Porte Counties IN.
We plan to keep the updates coming here at wgntv.com on our Severe Weather Blog as well as on our reports over WGN TV and radio. Stay safe and thanks for checking out our blog!
Tom Skilling
A large portion of the Chicago area will be under a Winter Storm Warning starting tonight. For the very latest on the developing storm and a complete breakdown of which Chicago area communities are included in the warning, follow the link below to the WGN Severe Weather Blog.
We already are more than 10" above average on snowfall to date this winter. We only need about six more to bring our total to 38". That would match the average amount of snow we get in an entire winter. That shouldn't be hard to do with the prolonged, steady snow that will begin late tonight and last through Tuesday night. More than two dozen states have advisories, watches or warnings. Washington DC is bracing for more snow but not as much as the most recent storm.
This could end up being one of the biggest snow storms of the year as we are expecting anywhere from 6 inches to a foot of new snow.
In addition to the updates on CLTV and WGN Radio, you can follow the storm through my facebook updates at
www.facebook.com/TimMcGillWeatherGuy
or check out my twitter updates on
http://twitter.com/WGNWeatherGuy
A steady light snow is expected to spread into the Chicago metro area Monday afternoon and begin to accumulate later that night. There will be an extended 24- to 30-hour period of snow as low pressure passes to the south and tracks east. Winds will grow much stronger Tuesday, gusting in excess of 30 mph gradually shifting from the east to the north by evening. Snowfall will be enhanced by the northeasterly flow off Lake Michigan. Going into evening rush hour Tuesday, snow totals could range from 6 to 10 inches with more to come. As the storm center pulls away into Ohio, snow and winds will slowly diminish Tuesday night, but north to northwest flow will result in accumulating snows around the south end of the lake and in northwest Indiana into Wednesday.
Mid-Atlantic in storm's sights
Another low pressure center will be tracking through the south in concert with the low moving through the Ohio Valley, spreading rain over the Gulf coast states. The southern low is expected to swing northeast, moving off the North Carolina coast Wednesday, pulling moist northeast flow and additional snow back into the same Virginia, Maryland, Delaware, New Jersey area hit with one to two-foot snows last Saturday.
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