Spring Snow

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.

Snow on Saturday?

An interesting development for early April….

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.

 

 

 

Philly Weekend Weather Forecast

Once again, today’s (Friday) model forecast was far off target.  We were supposed to have clouds and showers throughout the day.   Not the case!

I’m not so sure we can count on the model’s weekend forecast to be on target.  It appears that the NAM did better than the GFS so we’ll go with it.

The NAM shows heavy rain Saturday morning, ending early afternoon. (The GFS also shows some rain, but significantly less.) Clouds break late Saturday afternoon as winds pickup.  High about 60.

Saturday night becoming very windy and cold as low pressure tracks through Pennsylvania.  Chance of a wet snow flurry!

Sunday, mostly sunny, windy and chilly.  High 45.

I may need to update this forecast.  A bit below usual confidence.

Update Saturday 6AM:  The NAM has showers into early afternoon today (QPF 0.26 inches water), then some brightening skies possible mid afternoon before some more clouds move in towards evening.  Still a chance of a quick sprinkle in the late afternoon.  A wet snow shower increasingly likely around midnight as winds pick up.

For Sunday, mostly sunny, very windy and chilly.  Winds subside in the afternoon.  High 44.

Weather… and Other Things 'Up in the Air'