Sunday, January 27, 2013

Skate-a-rama For Some Tomorrow

Winter Weather Advisories are out for everyone along and northwest of I-95 for a chunk of Monday.  Advisories are out until 2 PM for the Delaware and Lehigh Valleys, plus Berks County, and until 11 PM for the Pocono counties in Pennsylvania plus Sussex County, NJ.

Modeling continues to hint strongly at a burst of precipitation moving into the region during or just after the morning commute from the west.  The NAM is arguably the most aggressive in showing the potential for this burst arriving early enough, with the atmosphere cold enough, to generate a brief shot of snow across portions of the region before temperatures warm aloft and snow transitions over to a period of freezing rain and sleet.


Any shot of snow will be brief and probably won't accumulate much -- coating type accumulations seem to be the most aggressive scenario if snow does indeed fall around Philadelphia. As above freezing temperatures push in aloft, that snow will transition over to freezing rain and sleet. However, because the surface will remain cold despite temperatures in the atmosphere near or just above freezing, the surface could freeze up with any precipitation that does fall.  The result will be some slick travel into the mid afternoon in the Lehigh Valley, probably into the evening hours in the Poconos.  You can see the surface profile on the NAM below for 2 PM where temperatures are at 32 or below from Allentown and Easton on north.   Precipitation may be winding down (the graphic below shows the six hours prior in terms of how much falls) but temperatures will be slow to climb so travel, especially as you head north, will be slick tomorrow.


As the graphic above alludes, precipitation amounts will also be heavier to the city's north where a quarter to a half inch of precipitation (liquid) is expected to fall.  Some of that will fall as snow, perhaps a couple of inches, with the remainder freezing or frozen precipitation before ending as drizzle.  Locally, any snow shot would be brief and amounts would be minor -- again, coating seems to be the snowiest bet.