Storm timing

The Chicago area will make it through most of the daylight hours today dry, or “snow free”. 

By 4PM the leading edge of the snow will be approaching the southwest suburbs, and should overspread most of the area by 8PM.   The snow is expected to fall at a steady pace through most of the night tonight, with periods of moderate to heavy snow (heavy snow defined by  visibility restricted to 1/4 of a mile or less) possible.

This system is expected to move through the area a little more rapidly than thought yesterday, and the quick departure of the storm will likely hold snowfall totals under 9″ in most locations.  As it stands right now, the majority of the accumulating snow should be over with by 10AM Monday morning.

4PM-8PM:    Snow begins

8PM-6AM:    Steady snow- moderate to heavy at times

6AM-10AM:  Snow tapers or diminishes to flurries

10AM-6PM:  Occasional flurries- no additional accumulation

Storm update: No warnings yet; Winter Storm Watch continues…

A Winter Storm Watch continues for much of the Chicago area, generally north of Interstate 80.   The bulk of the precipitation from this storm is expected to occur tonight (Sunday night), and will begin to wind down on Monday morning.

The latest suite of computer model guidance that arrived into the WGN Weather Center early this morning suggests this storm will be

1) a little weaker

2) tracking a little further south

3) moving out earlier than projected yesterday

 

The Bottom Line

The storm is still on the way.  As it stands early this morning, the majority of the Chicago metropolitan area will likely end up with 5″ to 9″ of snow.  There will be some exceptions to that range.   1) A narrow band of locally heavier totals (up to 11″) is still possible.  Just where this narrow band occurs is a tough call.  Right now, the most likely location would be north of the I-88/Eisenhower Expressway corridor.     2) The southern suburbs and portions of northwest Indiana may see some sleet mix in with the snow, resulting in a lower accumulation there.     

Be sure to check back with us here on the WGN Severe Weather Blog, as this is a very fluid situation.   A new round of guidance begins to arrive around 9AM, and we will be providing updates throughout the day.

  WGN Weather Center 7 Day Forecast 

Early evening computer guidance indicates forecast still on track

A Winter Storm Watch continues in effect for most of the north and central portions of the Chicago metropolitan area from evening through Monday evening.

A brief glance at the early out from the evening cycle of computer guidance indicates the current forecast appears on track. The WGN Weather Center will continue to monitor this developing weather situation and provide the latest updates and trends on this potentially major snowstorm for the Chicago area.
To summarize.. the onset of snow is expected late Sunday afternoon or evening with heavy snowfall of 6 to 12 inches across much of the north and central portions of the Chicago metro area including the City of  Chicago by Tuesday morning. Amounts are expected to taper off the the south to 2 to4 inches as the snow mixes with or changes to sleet and rain for a time Sunday night and Monday as warmer air gets drawn into the system.
If current trends continue, it is expected that the National Weather Service will issue a Winter Storm Warning for areas expecting the heavy snow early Sunday morning. Winter Weather Advisories will likely be issued for southern portions of the area where mixed precipitation and lower snow totals are expected.
The snow is expected to be heavy and wet and will be difficult to shovel, unlike the snow that fell earlier this mornth that was light and fluffy.
 
WGN Weather Center 7 Day Forecast
RED:         Winter Storm Warning
YELLOW:  Winter Storm Watch
WHITE:      Winter Weather Advisory

Heavy wet snow likely later Sunday night into Monday

Snow is expected to begin Sunday afternoon and spread north, possibly mixed with some sleet in parts of the area near and south of Interstate 80. As the center of low pressure tracks across southern Illinois into central Indiana, snow will increase during the evening hours. A little before midnight will begin the period when snow will fall the hardest in the Chicago area, perhaps as much as an inch an hour in some areas. Travel conditions will deteriorate rapidly and roads will become slick and hazardous. By early Monday morning rush hour, snow totals will probably range from 3 inches far south to over 6 inches on the north side of the metro area. This will be a heavy wet snow with storm total water equivalent in excess of an inch possible.
Cold air follows
As the storm moves east, snowfall will taper off later Monday morning with light snow or flurries continuing into the evening. Storm totals will probably range from 3 to 5 inches south to over 10 inches north. Behind the storm, with a strong northerly jet stream in place, frigid arctic-source air will flow south with the southern edge of this cold air mass pouring over the Canadian border into the Midwest. High temperatures in the middle 20s will be about the best Chicagoans can look forward to Tuesday through Thursday. A cold front could give a period of snow Tuesday night into Wednesday.

When wind chill drops below 32 degrees

Dear Tom,
An office debate is raging about the meaning of wind chill temperatures and we are turning to you for clarification. When the temperature is 33 degrees and the wind is creating a wind chill of 23 degrees, will that cause water to freeze?
–James Scobie

Dear James,
It will not. Wind chill is perceived air temperature, not actual air temperature. Air removes heat from any object warmer than the air itself, and moving air (wind) removes heat more rapidly. Wind chill describes the rate at which heat is lost from our skin, not the temperature to which skin will be cooled.
Wind chill is the fictitious temperature of still air that would remove heat from our skin as quickly as the existing combination of air temperature and wind is actually removing it. Air at 33 degrees cannot cause water to freeze, regardless of a wind chill temperature well below water’s freezing point of 32 degrees.