Latest NAM FOUS data just became available.

Precipitation starts at midnight as rain, gradually mixes with and changes to snow towards daybreak.   Snow ends between 7-9 AM.  Total QPF is now 0.46 inches water.  Most of this will fall as rain or rain mixed with snow, becoming all snow by 5-7 AM.   Still impossible to predict accumulations, because of warm ground temperatures, melting due to mixed precipitation and varying amounts of cold air at the surface.  (Temps expected to fall to 32 by 7 AM).   More QPF at the coast, but warmer temps.  Precipitation drops off far north and west.

While impossible to predict accumulations with any confidence,  if you’re looking to hang your hat on a number, I’d say between 0.5 to 2 inches, especially on grassy surfaces outside of Center City Philadelphia and near suburbs.  This is a low confidence forecast.

Tomorrow’s precipitation is a perfect example of how poorly the models have been handling the extended range forecasts (more than 4-5 days out) this winter.  Just 3 days ago, this precipitation had been expected to stay to our east, just brushing the coastline.  Things clearly have changed. 

With short range forecasts so changeable, the “long range” period- Monday through next Wednesday- presents a large forecasting challenge, as there are several potential coastal low pressure systems forecast to develop,  with low confidence in each scenario.