Saturday, February 11, 2012

Damp Chill, More Snow Showers Later

 The city and the immediate suburban counties to the south and west remain under Winter Weather Advisories this morning as light snow falls generally above the Garden State Parkway across the region from the Atlantic City Expressway on south...with rain at the South Jersey Shore likely to change over to a mix and then light snow over the next couple of hours for a time.   It's not a heavy snow by any stretch as precipitation didn't "burst" as much as some of the models were indicating yesterday.  With that said, coating to an inch accumulations seem commonplace across the Delaware Valley and northwest suburbs in the first burst of the event.

Precipitation will taper off to drizzle or snizzle, fo shizzle, for a while across the region as this first burst moves away after 9 or 10 AM.  Temperatures may moderate towards 40 around midday in the city and South Jersey, with mid or perhaps some upper 30's across Pennsylvania in the intermission between "halves" of this "half-a-storm".   Our high is probably set to occur just after midday at the "height" of the intermission.  The second half of the system will move in after 4 PM in association with the cold surge that will push down for tonight.   This burst of snow is currently seen on radar up over Lake Ontario/Erie and Western Upstate New York as of 6 AM.  It will drift south and southeast through the day, pulling the cold front east with it (that's out west of Pittsburgh where light snow is falling as well)...the result will be increasing wind, decreasing temperatures, and a second burst of snow between 4 and 9 PM across the region.

The higher resolution modeling does a pretty good job of pinpointing where heavier bands of snow may set up...and in this particular case it has been suggesting a steadier band of snow will set up across Central Pennsylvania this evening and drop a couple of inches (perhaps a notch more than that) in a band from Selinsgrove to Lancaster to near Dover as this energy pushes through.  An inch to two inches isn't out of the question just east of that line, including the western suburbs of Philadelphia, as the band works through.

There was some talk of "flash freezes" and arctic surges tonight.  Yeah, temperatures are going to drop after 4 PM across the region as the cold front moves in.  However, we aren't looking at fifteen to twenty degree temperature drops and everything freezing up with a snap of a finger.  Temperatures will drop about three to four degrees per hour over a three hour window, with temperatures dropping into the 20's after sunset.   The snow showers themselves will probably contribute more to poor visibility and some less-than-stellar travel across the region this evening as they move through since temperatures will be dropping and the snow showers will have a better chance to stick on untreated surfaces than this morning's pittances of snow.   It's not going to be ideal out but it's not like we're seeing temperatures drop 20-30 degrees in a short window.

By Sunday morning, temperatures will likely be less than 20 north of Philadelphia, in the low 20's in the city proper, with wind chills in the single digits north and right around 10 above in the city.   While cold, it's not the coldest morning we've seen nor will Sunday be the coldest day of the winter...we'd have to avoid hitting 29 somehow, which is quite unlikely.