A quick update. Latest NAM shows a significant snowfall for the PHL area, starting after midnight Wednesday and continuing into the morning on Thursday. Temperatures for the storm have continued to drop, the low pressure system in more intensified and slower. Current QPF values are over 0.60 inches water which translates into over 6 inches of snow.
This situation continues to change. Stay tuned.
Today’s early morning run of the NAM showed a significant change from the warmer and wetter run of yesterday evening.
Here’s the trend- Intensification of the low pressure system developing on the frontal boundary has increased, while the speed of the system has slowed. As a result, the precipitation starts as rain after midnight, but changes to snow during the early morning hours on Thursday. The NAM shows a few hours of moderate snow, ending about 10 AM. (Areas to the far north and west will have much greater accumulations, as the change to snow occurs much earlier.).
Last night’s GFS still showed a somewhat faster and warmer system, but the trend is towards intensification and somewhat slower speed. The slower speed allows more cold air to enter the area.
The Thursday morning commute looks to be a challenge, as some snow, and cold gusty winds move in.
Still too soon to predict specifics regarding accumulation and exact timing.
The models continue to show low pressure development along the cold front that moves through late Wednesday afternoon. The latest GFS model cranks out over 0.65 inches of water.
The upper atmosphere cools down by the start of the precipitation, BUT the models are showing surface temperatures in the immediate PHL area not dropping below freezing. (Areas to the far north and west will have several inches of snow, if the current model forecast remains intact.)
In the the immediate PHL area, precipitation looks like it will fall as very wet snow and accumulations are likely to be limited by warm ground temperatures and warm surface temperatures. That said, it will be falling during the night time, and ice and some accumulated snow will be an issue for the morning commute on Thursday.
Right now, the low pressure system looks like it will have moved away from us shortly after daybreak on Thursday. However, the QPF values and speed of this system have continued to change and the current trend has been intensification. Stay tuned.
Tonight’s NAM model has it too warm for snow Wednesday night in the immediate PHL area. Upper atmosphere too warm and too warm at the surface. Things may change.