Last Updated 4 days ago

Things continue to evolve with the forecast. Tonight’s NAM and NBM data just became available.  QPF values of less than 0.08 from now until the changeover to sleet about 7 AM is expected to limit snow accumulations to a coating or less than 1 inch.

Temperatures at the surface will be marginally cold enough to prevent much if any accumulation in the city proper, except on some surfaces.

North and west of the city, temperatures are forecast to be 31-32, but the increase in precipitation rate about 7-8 AM will correspond with the changeover to sleet and some freezing rain.  Some accumulation of sleet is possible.  Larger accumulations of sleet and snow will be an issue primarily in the far northwest suburbs. 

This will be a messy storm, but most of the precipitation will eventually fall as rain in most areas.. A mix of precipitation is possible until mid to late morning, then rain.

The GFS will be available in an hour or so. I’ll update if the GFS is significantly different.

Last Updated 5 days ago

from earlier today:

The latest NAM and GFS data has become available.  Both models have returned to their earlier predictions of having the precipitation suppressed to our south for the balance of the day by cold air that is building in from the northeast.  So cancel that snow for the daytime hours.

Both models maintain a very cold low level flow from the northeast, while upper winds bring warmer temperatures aloft.  A complicated forecast.

For Philadelphia and immediate suburbs:   Both models have the precipitation moving back to the north Monday evening.   The NAM and GFS has snow returning northward to our area between 8 and 10 PM tonight.   Depending upon your model of choice, about 2-4 additional inches of snow will fall tonight before 5-7 AM Tuesday.

Temperatures at critical levels of the atmosphere will rise and cause the precipitation to mix with and fall as sleet.  This should happen between 5 and 7 AM Tuesday morning, but somewhat later in the far northwest suburbs. 

Sleet will fall in the early morning and mix with and change to freezing rain, and then all rain by about noon.   There is the possibility that this transition to rain may be delayed, especially in the far northwest suburbs.

Heavy rain for the balance of Tuesday.  Total QPF for this storm will be about 2.0 inches of water, falling as snow, sleet and rain as outlined above.

Updates later this evening.