Thursday AM update: Last night’s  1 AM run of the GFS model shows some interesting trends- a significant increase in the QPF to over 0.40 inches water and a somewhat earlier start. The GFS is running colder too.   The NAM also showed a change, staying at a lower QPF of 0.15 inches water, but now starting later,  after 7AM.

This looks like it might be a tougher forecast than previously thought.  Will have to wait until tonight’s model runs to pin this down.

Today’s model runs continued with the likelihood of snow starting during the hours before daybreak Friday and continuing into the morning.

Some of the precipitation before daybreak will fall as rain mixed with snow, but a change to all snow is likely by or before daybreak Friday.  The NAM has rejoined the GFS in having snow.  QPF values have been in the  0.10- 0.25 inch water amount.

(Tonight’s NAM model just became available and has reduced the QPF value to 0.15). 

As discussed in my post from Tuesday, predicting accumulations in March with such low QPF values is really an academic exercise.

Surface air temperatures may not fall to 32 and will rise during the morning.

That said, it appears that a coating is possible at daybreak Friday, mostly on grassy surfaces. Not much more than that will occur.

Driving conditions will be minimally impacted in the immediate PHL area and surrounding suburbs, as little is expected to stick on roadways, especially after daylight returns.

Temperatures are expected to plummet later Friday afternoon and nighttime.

Another post from over a week ago suggested a possible major snowstorm  for the period around Monday March 13th.  That scenario seemed to  fade, but the latest models are again suggesting the possibility of a significant coastal snowstorm on Tuesday March 14th.

Continuity of the model forecasts  have been poor this season, but the situation next Tuesday needs to be watched.

I’ll update Friday’s forecast Thursday night, about 9:45 PM.