Tonight’s NAM model data has become available. Here are the trends– the NAM has reverted back to its forecast from a day ago. The storm is a bit less developed and a bit faster. Total QPF values about 0.70 inches water with the heaviest snow ending about 8-9 AM Thursday.
Based on temperature profiles, the precipitation starts as rain or rain mixed with snow about midnight Wednesday and changes to snow sometime between 3-4 AM, then continues as snow until 8-9 AM. Warm surface temperature before the storm will reduce snowfall accumulations. Best guess is about 4 inches in the immediate PHL area, up to 6-8 inches north and west, less in southern NJ.
This afternoon’s GFS had much higher QPF values and greater intensification of the storm. ( Tonight’s GFS model data won’t be available until later tonight.)
Will update tomorrow morning, but we won’t really have a handle on this storm until Wednesday evening’s model runs.
A quick 11 pm update- the latest GFS is similar to the NAM – QPF similar (0.89) and ending earlier about 7-8 AM
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.
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.
