Philadelphia Weather Outlook

Friday Weather Update

This morning’s models continue showing precipitation starting Friday morning about 8AM  and ending Friday evening.

Temperatures at the surface will be around freezing (the MOS lately has not been very accurate with temperatures).  Temperatures in the lower levels of the atmosphere will support snow through early afternoon.  Temperatures in the upper atmosphere just marginally support snow.  QPF values have increased to over 0.65+ inches for both the NAM and GFS.   With heavier precipitation rates, dynamic cooling might make temps a bit colder.

Areas to the north and west of Philadelphia are more likely to have snow accumulate.

So a messy day for Friday.  Right now it looks like much of the day it will fall as wet snow, but accumulations will be limited, especially on dark asphalt roadways.  A change to rain is likely after 3 PM.

Everything is right on the edge of being a rain event, so it would not take much for the expected snow to fall as a wet mix or just rain.  Right now, I’m betting on it coming down as snow, likely changing to rain during the mid afternoon on Friday.

Weather Updates

Winter Weather Update

Both the NAM and GFS have low pressure moving along a frontal boundary to our south and intensifying somewhat as it moves over the coast Friday.

Thermal profiles in both models support snow, however temperatures at the surface will be close to 32.  With QPF values of about 0.45 inches water, this would be a significant storm IF it were winter.

However, it’s March, the sun angle is high and insolation through the clouds challenges accumulation on roadways.  The snow will be occuring,  not a night, but during the morning and afternoon.   So  accumulation on grassy surfaces and sidewalks is possible,  but accumulations on roadways will be limited and short-lived.

Too many factors to really be able to predict accumulations accurately.  Best guess is an inch or two on grassy surfaces,  and a slushy coating on roadways.   The precipitation may be heavy during the afternoon, so visibilities while driving may be poor.

This time of the year, weather forecasting has its lowest accuracy, so changes are likely.

Weather… and Other Things 'Up in the Air'