Today's Weather Discussion: White Christmas Update

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Meteorologist Trent Okerson

Friday, Dec. 24:

Happy Christmas Eve everyone....hope you have those final few gifts taken care of and are all ready for Santa's arrival tonight.  It still looks like Santa will need the sleigh for his rounds across much of the middle of the country, including much of the Local 6 region.  (To track Santa via NORAD's Santa Tracker, click here.) If you read yesterday's discussion, the forecast has really not changed very much, aside from some timing details.  Snow has already started falling this morning across parts of SEMO & S. IL....places like Farmington, Perryville, Carbondale, & Murphysboro have been among the first spots to see the flakes flying.  Here's what Ultimate Doppler looked like as of around 8AM this morning:

As we look at this radar image, there was snow falling where you see the brightest shades of white, but most of the rest of the radar returns were not reaching the ground.  This is a phenomenon called "virga", where a layer of very dry air just above the surface of the earth causes precipitation showing up on radar from a bit higher in the atmosphere to evaporate before reaching the ground.  This process will continue until the atmosphere becomes fully saturated with moisture, and then the precip will fall all the way to the ground.  That is already the case in SEMO & S. IL, where snow is reaching the ground.  As snow spreads farther south and east, it may initially evaporate until the atmosphere fully moistens up. 

 The Winter Weather Advisory issued yesterday for parts of the Local 6 region was expanded south a tad bit this morning, and with the earlier arrival of the snow, will expire at 6AM tomorrow.  Here is the latest map of the advisory area (advisory in purple):

Snow totals from yesterday's forecast are about the same.  There have been some subtle changes in the forecast models, but not enough to lead to a reason to change the forecast.  Still thinking generally  2-3" along and north of Route 13 (maybe pushing 4" locally in a few spots), 1-2" for the rest of the advisory area, and a dusting to 1" south of the advisory.  Here are some of the forecast models/images I have sifted through this morning, as well as the snowfall forecast I put on air this morning:

                         06Z (midnight) GFS Bufkit data....estimates 1.4" snow through noon Sat. for Paducah.

                                                               GFS snowfall accumulation

                                                        NAM snowfall accumulation

HPC/NOAA probability of at least 1" of snowfall through 6AM Sat.

HPC/NOAA probability of at least 2" of snowfall through 6AM Sat.

Snowfall may lead to some slick spots on roadways tonight, especially in Southern IL and Southeast MO, as well as some reduced visibility.  Overall though, this doesn't look like a huge-impact event when it comes to travel.  If you have travel plans, here are the latest interstate forecasts:

That's the latest as of this morning...Jennifer will have the latest tonight on Local 6.  Merry Christmas!

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