Warm, spring-like weather has been conspicuously absent for much of May. However, a late spring and more summer-like pattern is evolving in the Atlantic, where a Bermuda high pattern is expected to establish itself over the next few days into the weekend.
Warmer temperatures and higher humidity is expected for Memorial Day Weekend. It is unknown whether the Bermuda high will be strong enough to fend off showers and thunderstorms that are depicted to develop to our west, south and north.
Right now, the GFS model is keeping us dry through the weekend, from Saturday through Monday. But the model trend has been for a weakening of the high pressure dome which may allow showers to sneak in if the trend continues.
So it looks to be a nice weekend here in Philly and at the NJ shore, but it wouldn’t take much for that forecast to go bust.
The models continue to show an area of vorticity to cross our area on Saturday and induce development of a coastal low. Precipitation is expected to develop Saturday morning and now continue into the afternoon. Temperatures are expected to fall during the day.
The upper air profiles suggest wet snow is possible at the onset, despite temperatures too warm to allow accumulation. But as temperatures fall during the day, some grassy surface accumulation is possible in the afternoon and icy conditions are possible Saturday night.
Friday 7 AM Update: Last nights models show earlier surface development and greater intensification of this coastal system expected to to form from a clipper-type vorticity passing over us.
The. NAM cranks out a QPF as much as 1.00 inches water during the daytime hours of Saturday. This high QPF is likely over-done, but it does suggest a cold windy day with rain/wet snow for much of the day on Saturday. Impossible to determine snow accumulation, but expect some snow accumulation on grassy surfaces during the afternoon hours with possible icy conditions Saturday night. If precipitation rates increase, temperatures may fall below those predicted by the models. Areas north and west may truly have a significant snow accumulation.
Over the past week, the GFS has consistently shown the development of an amplified upper air trough for the eastern US allowing cold air to filter into our area for the weekend. Additionally, the GFS has been showing a mid level vorticity to dive down through the upper trough, bringing precipitation in the form of snow to our area from daybreak Saturday through the early afternoon. The GFS has a QPF of over 0.30 inches water. This could potentially translate into an inch or two of snow on grassy surfaces by the end of the day.
The vorticity is expected to develop into a coastal low pressure system, but currently expected not to linger.
Thursday PM Update: Latest model data still supports very wet snow for Saturday morning. It’s not likely (with current surface temperatures) that there will be an accumulation that affect travel, but some accumulation is possible on grassy surfaces. Current NAM QPF is 0.39 inches water. An interesting weather event for early Spring, after what was a rather easy-to-take winter.