Wintry weather is likely to be the last thing on Chicagoan’s minds moving forward this week since temps Wednesday are to move within striking distance of 60-degrees. Temps Tuesday have moved broadly into the low 50s. Readings Wednesday are to have a springlike feel to them. But it’s worth remembering that Chicago’s weather records include a host of late season winter storms which have swept into the area and produced major snow and/or ice only days after unseasonable 50 to 60-degree warmth.

The basic constructs of this system and its likely impacts on Chicago later this week are clear. There will be significant precipitation and it will fall in a howling northeast wind.

Early guidance on where accumulation of ice and or snow is most likely in the Friday/Friday night time frame produced by the National Weather Service’s Weather Prediction Center (WPC) in Maryland.

‘Heart Attack’ Snow Possible

Precisely where snow dominates in its precipitation shield will be the focus of attention in coming days. One thing’s for sure, where that snow occurs, it will be wet, heavy and a devil to shovel because of its weight—what’s often referred to as “heart attack” snow. And it may not be hard for this system to produce a foot of the white stuff within the hardest hit areas impacted by its heavy snow band.

Full forecast details at the WGN Weather Center

 But precisely where that heavy snow band is to lay out isn’t yet clear. But this storm is not yet within range of our higher resolution forecast models which, when blended to our global models, will offer a much clearer picture on precisely where its heavy snow band with this storm will lay out. Chicago is going to be close enough to such a band, it’s worth of keeping a very close eye–especially if if you have any travel plans toward Friday–particularly if you heading north and west.

The NWS GFS ensemble model’s estimate of total snowfall in the coming 7 days laying out this system potential significant snow ares. This is but one model’s take. Blending a range of models–including higher resolution short range models–which will take place in coming days, yields a far more accurate and complete picture of any storm’s snow production capacity

Wintry Mix Details

The form Friday’s wind-driven precip will take are not yet carved in stone but will become clearer as the system approaches in the days ahead. Though some models sock Chicago with snow, others suggest heavier snow will stay north and that a wintry mix is likely to be out.

You’d have to say looking at modeling at this moment that a high probability scenario would be rain or a wintry mix is to develop in the city late Thursday night into Friday morning. Chances rise that the liquid or mixed precip might well transition to wet snow as storm dynamics cool the atmosphere and take the precip from liquid form or a mix over to crystalline form. But refinement of that thinking is to come–and I’ll keep you posted.

A 180+ mph jet stream speed max (i.e. “jet streak”) is diving southward from the Gulf of Alaska and powering this storm.
Closer look at the 6am CST Tuesday 250 mb analysis from Environment Canada
NWS GFS ensemble forecast panels—thie one for Noon CST Thu

What is leading up to this storm

The latest in what has been a parade of active winter storm systems is diving southward along the west coast. These system, including Monday’s rain and small tornado producer here, followed a similar track in sweeping from the Pacific and California across the Rockies and Southern Plains then northeastward into the Midwest.

This one is to impact the Chicago Thursday night into Friday night in a colder environment than the last two. Wind and another significant round of precipitation are likely.

Like its predecessors, this is another we’re watching closely, but time is on our side. We have two days to refine thinking on its ultimate impact(s) here in Chicago.