The models had under-played the light snow that has developed this morning.   Looking at what’s going on here….The snow is the result of a small area of mid-level  convergence and a localized area of isentropic lift that has developed right over the PHL area as an upper air disturbance moves through.

Short range models (NAM-based HRRR and the GFS-based LAMP hardly show this, but the LAMP has it ending about 9 AM.  Of course, they didn’t really get it right to begin with, so we’ll have to see.

Weather is so amazingly difficult to predict sometimes.

There may be sun out right now, but the models are consistently showing snow to begin in PHL by 1 PM today.  Latest NAM model has been consistent in cranking out a QPF of > 0.80 inches of water, with about 0.40 inches falling as snow.   I’m still going with 4-7 inches of snow in PHL before a changeover to sleet and freezing rain.

The trend has been for an extended period of cold air at the surface to remain in place, even if the upper atmosphere warms a bit.

The changeover to sleet and rain  will tamp down final  snow totals however extended period of surface temperatures below freezing  will likely cause extensive icing, especially north and west of Philadelphia.  Driving later this afternoon and this evening may be very difficult.  Large storm snow totals sound impressive, but this sort of snow to ice mix can be more dangerous.

I don’t think this is going to be a storm where the rain washes the snow and ice away.