Sunday, March 17, 2013

Snowy, Perhaps Icy, For A Time North/West Tomorrow Night

The next storm system in the pipeline of March Madness will move into the city tomorrow around midday or into the early afternoon hours. While temperatures at the surface may be a bit above freezing at the beginning, they won't be where snow develops within the clouds. The result will be light snow initially for many spots from Philly on north.

The city and immediate suburbs probably don't get much more than a light coating of snow on grass and perhaps cars as precipitation moves in during the midday hours.  It may be a bit of a "thump" of steadier precipitation to the city's west and northwest, which may yield a little more than a light coating for the outer burbs such as Quakertown and Pottstown, but in the city and immediate burbs accumulation totals on grass should generally be in the "less than one inch, if that even" category.

Milder air aloft and at the surface will push north and northeast through the evening hours, with snow transitioning over to rain relatively quickly in the course of the event around here and across the suburbs.  That transition will take longer in the Lehigh Valley, Berks County, and Poconos.

By 8 PM, our region should be in general rainfall.  However, there's a question of how quick temperatures will moderate above 32 across the Poconos, upper Lehigh Valley, and northern Berks County.  The GFS is showing the possibility of icy rain and sleet across those areas tomorrow night...granted, it has a colder bias of sorts in the model so this amount of chill may be a bit overdone.  That said, it would not shock if there's a transition period from snow to rain with something in between, probably sleet although some freezing rain is doable.  Best chances for this would be for along and north of I-78, especially in the Poconos.
Later at night, most of the transition from frozen to nonfrozen will have taken place through most of the region, with perhaps a threat for icy rain and sleet remaining north of I-80.  Rain could be steady to heavy at times during the overnight hours, with an inch of rain possible for Philly, the I-95 corridor, and points west.

In terms of total snow accumulations, odds favor coating type accumulation locally, with an inch or two along I-78 (Allentown to Reading) plus across the Quakertown and Pennsburg parts of the suburban counties. The Poconos could see 2 to 5 inches of snow from tomorrow and tomorrow night's wintry portion of precipitation.