Tonight’s NAM data just rolled in. QPF values are again very low in the immediate PHL area, about 0.09 inches water. With some of that falling before surface air temperatures fall to 32, it would appear that the best guess is a coating to 1 inch in PHL and the immediate suburbs.
Areas farther north and west may have 2, possibly 3 inches.
The biggest issue, regardless of accumulation, will be that any wet accumulations will become icy in the morning, with temperatures dropping below freezing for a time. Stay safe!
This afternoon’s GFS and NAM have maintained a low QPF of less than 0.10 inches water in the immediate PHL area and south. Under ideal conditions, we would have about an inch or so of snow. HOWEVER, the surface temperatures have been above freezing today and won’t drop below 32 until 4 AM. While the heaviest QPF is expected between 4 and 7 AM, the warm surface temps will likely cut into accumulations.
So…still going with about 1 inch of snow in the immediate PHL area an adjacent suburbs. Area north and west (Doylestown, Allentown) may have closer to 3 inches. Again, a difficult forecast, since warmer surface temperatures will be reducing accumulations.
Whatever falls, there is agreement that temperatures drop below freezing for the morning rush hour. So icy conditions will be an issue.
Tonight’s NAM data first becomes available about 9 PM or so. I’ll update then.
This morning’s GFS model continues with the trend of low QPF of 0.09 inches water, similar to the NAM. This translates into about an inch of snow, assuming colder temperatures. But surface temperatures may be at or just above freezing for some of the time, reducing accumulations even further. So a coating to 1 inch of wet snow is still the best guess for PHL and surrounding suburbs, more north and west.
Still a lower than usual confidence forecast, since the higher resolution NAM shows greater QPF values and some of the other models suggest the same.
Whatever falls likely causes icy conditions, as temperatures are expected to drop early Wednesday morning.