In my neck of the woods, just northwest of the city, a coating of sleet and freezing rain is accumulating. The QPF was a bit higher than I predicted last night; a few heavier areas of precipitation allowed some “dynamic cooling” and some snow flakes were able to develop briefly, but essentially it’s been sleet and freezing rain in PHL and the immediate suburbs.
Temperatures are still expected to rise above freezing about 10 AM or so. Rain is expected for most to the day, heavier in the afternoon.
The latest NAM data is becoming available. Precipitation, very light, expected to begin about 7 am Wednesday. As I’ve been saying since last night, temperatures in the upper atmosphere will be too warm to support snow in Philadelphia and the immediate adjacent PA counties and south Jersey.
In the lower levels of the atmosphere and at the surface, temperatures remain below freezing until 9-10am in and around PHL, so precipitation will fall as a brief period of light sleet and then light freezing rain, changing to all rain by late morning.
The issue for tomorrow morning will be icy conditions on untreated surfaces, not accumulations. Even a thin coating can be slippery.
One more thing…QPF values are very low in the morning, less than 0.09 inches water. The heavy rain will be during the afternoon.
The 1 AM NAM model run has extended the duration of the light snow to about 10-11 AM. Expect possibly an additional 1/2 inch of snow after sunrise in PHL and immediate surrounding suburbs.
Temperatures are expected to drop below freezing, causing icy conditions.
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!