Monday, March 18, 2013

Precipitation Spreads Northeast Through Day

Today's rain, sleet, and snow is on track to spread in over the next several hours, with no real changes in our thinking regarding what will fall.  Still anticipating a general coating of snow and slush in the city, more north and northwest.

The GFS and NAM are still in agreement on a relatively non snowy solution for the region, with any snow and sleet quickly transitioning over to rain from south to north through the evening hours.  Most locations locally wouldn't see much snow at all -- temperatures aloft and the surface warm sufficiently and transition light snows over to rain during the PM rush hour.

The exception on this is the European computer model, which is a bit colder aloft with temperatures and suggests a bit heavier precipitation moving into Philadelphia during the late afternoon hours.  The Euro scenario has a bit of support from the UKMet model in a slower push of warmth aloft although it's not as robust on precipitation as the Euro is.  This would result in a bit more snow moving through during the course of the early evening, resulting in more impacts on travel.  The Euro thinking is a marked shift from its run twelve hours ago so in this case there's a lack of consistency in modeling from the Euro, at least compared to the GFS and NAM.  

If the heavier burst of precipitation overhead, as modeled by the Euro, pans out, we might see a bit more snow on the front end but odds would favor this being more of a grass and car accumulation, less a roadway threat.  However, it may result in a rather slow drive home if such a scenario pans out.  The Euro scenario would also yield more snow to our north and northwest as the transition to rain would be delayed. This would be more of an issue for the Lehigh Valley and Poconos than locally.

We should see the first drops and flakes into the city after midday today, with the bulk of precipitation falling after 4 PM and through Midnight.  The city is still on track for a total of just shy of an inch of liquid equivalent precipitation, some of which on the front falls as snow or sleet.