The latest NAM and GFS model data has become available. Here are the trends: Both models have the precipitation arriving earlier than previously predicted on Sunday.
The snow will start in the early afternoon.
As always, the NAM has a higher QPF than the GFS, with almost 0.47 inches water falling. The NAM is also colder than previous model runs. The NAM has done well with temperatures, but has been over-stating QPF.
So there is the possibility of accumulating wet snow Sunday afternoon into Sunday evening before a changeover to sleet and freezing rain during the evening. 1-3 inches snow possible. It’s difficult to determine accumulations- higher sun angle this time of year, so roadway surfaces tend to not develop as much accumulation during the day.
Cold high pressure will bring fair skies and cold temperatures to our area on Saturday. Highs will be in the low 30s.
The high pressure system drifts east and a return flow of moisture will bring clouds on Sunday. Most of Sunday will be cloudy with high near 32.
Towards Sunday evening, light snow will develop but will mix with sleet and then freezing rain during the evening.
Since ground temperatures have been below freezing and the precipitation is occurring at night, a period of sleet and freezing rain may make driving difficult Sunday evening and night.
The sleet changes over to rain some time after midnight and ends about daybreak on Monday.
The models had under-played the light snow that has developed this morning. Looking at what’s going on here….The snow is the result of a small area of mid-level convergence and a localized area of isentropic lift that has developed right over the PHL area as an upper air disturbance moves through.
Short range models (NAM-based HRRR and the GFS-based LAMP hardly show this, but the LAMP has it ending about 9 AM. Of course, they didn’t really get it right to begin with, so we’ll have to see.
Weather is so amazingly difficult to predict sometimes.
