Friday, February 22, 2013

Perhaps Some Slick Spots Overnight North & West

Winter Weather Advisories were issued for the north and west for tonight and early tomorrow morning. Not because of the threat of snow but because of the threat of freezing drizzle across the region as temperatures aloft moderate and precipitation type transitions over from snow showers (assuming they happen later on today) to drizzle and freezing drizzle this evening.  Keep in mind any precipitation that falls this evening and tonight will be pretty light in nature -- we're not expecting hefty rates of precipitation in the first parts of this storm system since most of the energy will still be to our southwest and will not impact us until late tonight (south) and tomorrow (rest of the region).

Temperatures from the city on south will be sufficiently warm tonight -- mid to upper 30's -- that slick spots will not be likely and even if snow does fall initially, temperatures will be mild enough at the surface and precipitation light enough that there won't be an issue.  North and west is another story.  Temperatures in the Poconos, Lehigh Valley, perhaps some of the colder nooks and crannies in the outer burbs may hover around freezing overnight tonight or be a degree or two below that in the Poconos.  While the snow shower part of the event, which really shouldn't last that long, won't be a huge impact on travel any transition to drizzle or freezing drizzle with surface temperatures around 32 may cause a few slick spots.

The transition to solely drizzle (removing the icy drizzle part) takes place late tonight and tomorrow morning as the surface temperature begins to moderate above 32 as rain pushes up from the south.  Advisories will drop at 6 AM in the outer burbs, 10 AM elsewhere.  Rainfall on Saturday generally yields about a half to three-quarters of an inch in most spots, with the potential for a bit more than that north and northeast of Philadelphia.