Polar vortex will bring winter’s coldest temperatures, but no guarantee of snow (yet)

This is a depiction of possible cumulative 7day snowfall off the GFS model–but it’s currently alone in doing this.

CHICAGO — The southern flank of a polar vortex settling south will likely cause temperatures in the Chicago area to drop over the holiday weekend, but will it also bring a White Christmas with it?

It seems possible, but before anyone gets too excited, it’s important to note that so far only one model (the Weather Service’s GFS) hints that sticking snow could be headed into the Chicago area this weekend. You want more than one model on board before predicting snow is on the way, and that hasn’t happened yet.

As it stands now, indications point toward the chance of rain at the outset in Chicago Friday night, which would switch to snow in the early pre-dawn hours of Saturday, while northwest sections of the area would see all (or predominately) snow.

It’s not surprising people are eager to see snow in the area, though. So far, there’s been only 2.1″ of snow this season, as opposed to 17.7″ by this date a year ago. If the GFS model is correct, the northwest suburbs and areas to the north and west of Chicago appear to be favored by this model for accumulating snow Friday night into Saturday.

Temperature trends in Chicago and other sections of the Midwest explain why the ground is all but snow-free here. The normal high for December 19 is only 34 degrees, but Tuesday is the fourth consecutive day in which temperatures have reached or exceeded 40 degrees. Temperatures this month in Chicago are running at least 11 degrees warmer than over the same period last December, when we even saw temperatures drop to 13-below at O’Hare on the coldest day of the month. By comparison, our coldest reading to date has only been 16 degrees on December 14.

So while many are eager for snow this holiday season, at least it has been a warm December so far. That will all change though, because one thing all the models agree on: it’s going to be a cold Christmas. We’re heading for the winter’s coldest air to date, and as it sweeps in temperatures on Christmas Day will struggle to hit to 20 degrees as a high, and morning wind chills will likely be at or just below zero.

Check out this post on my Facebook Page for even more details: