Those of you who follow this blog know I’ve been wrestling with this forecast for Saturday evening.  There have been too many borderline conditions to accurately predict the precipitation type and accumulation amounts.

The latest NAM data has become available. QPF values have been incredibly consistent at about 0.60 inches water.  Surface temperatures appear to be above freezing for much of the day and near to above freezing during the storm.  Mid-level atmosphere temperatures appear  slightly too warm to support snow, while lower temperatures are at or below freezing.

After an initial start as light snow between 4-6 pm, it  appears to be a mostly sleet and rain storm in Philadelphia and its immediate suburbs before changing back briefly to snow before ending after midnight.

A cause for error in this forecast might be dynamic cooling due high precipitation rate, which might increase the snow possibility.

Warm  surfaces will further reduce accumulations, except on grassy surfaces.   A wet, slushy 1 to 3 inches is a best guess on grassy surfaces, less on pavement.

There’s still 24 hours for things to clarify.

11:30 pm – Tonight’s GFS even less impressive QPF and warmer surface temperatures. Mostly a sleet and rain event for PHL and surrounding areas.