Tuesday, February 26, 2013

Winter Weather Advisories In Poconos, Rain For Most Everyone Else

Winter Weather Advisories are out in the Poconos for this evening through early Wednesday with tonight's storm system.  They, along with the northern fringes of Lehigh, Berks, and Northampton Counties, are the only areas that will have any real wintry issues to deal with.  For everyone along and south of I-78, this is a rain event that will bring an inch of rain, perhaps a bit more in spots. More on that in a bit.

In the Poconos, surface temperatures will struggle to get back above 32 despite a moderately mild day in advance of the rain.  Low level dry air will help knock temperatures back as precipitation moves in tonight due to evaporational cooling, with the result being temperatures that will drop to around freezing for much of the event.  Yesterday, a couple of aggressive runs of the NAM had suggested more snow and less icy rain across the Poconos and Central Pennsylvania mountains as a bit of an outlier to the majority of guidance. That trend is reversed itself in the NAM, with the model now in line with the GFS and Euro in showing icy rain and some mix of snow and sleet in higher elevations.  Temperatures aloft warm during the event so the transition to icy rain will take place during the night but with surface temperatures around freezing, though hopefully nudging above 32 during the event, travel may be slick in much of the Poconos during the night.

South of there, rain and wind move in during the evening rush and continue through Tuesday night.  The majority of the region picks up about an inch of rain, with the potential for a bit more than that south and east of the city, in addition to the Poconos, if the NAM is to be believed.  The GFS and Euro have more precipitation north and west of the city than south and east and generally flip the NAM's output around by placing heavier precipitation north and west of I-95. In any case, it's likely not enough to cause major flooding concerns but enough to send the usual suspect streams a good bit higher overnight and probably result in some minor roadway flooding in areas that tend to flood easily.

Rains will be steadiest and heaviest overnight so impacts on travel for the majority of the region should be minimal due to the timing of the storm system.