Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

Update Sat 7:15 PM— Today’s cloud forecast was spot-on. Sunday’s forecast below looks good as well with plenty of sunshine, occasional clouds. Some clouds move in later in the afternoon.

Word has gotten out about snow for Wednesday. Since that time period is over 90 hours in the future, the higher resolution models don’t extend into that forecast range, making snow accumulation forecasts quite unreliable. It was refreshing to hear the Channel 10 meteorologist refuse to make a snow accumulation forecast until Monday.

Nonetheless I’m sure people are curious about the snow accumulations being forecast by the longer range models. Snow is forecast to start before daybreak Wednesday, change to rain, and then change back to snow Wednesday night. Basically, snow accumulations are in the 0.5-2 inch range from just outside the city, with higher amounts possible towards Allentown and northwest NJ.

Curiously, most models have snow accumulations in our immediate area where surface temperatures are forecast to be over 32º. Again, too soon to make any ‘predictions’. Stay tuned.

Update Sat 7:30 AM— Last night’s models continue with the forecast of an area of cloud development Saturday directly over the Philadelphia area. The NAM NEST and the new CMC GEM models have brief clearing late morning before clouds redevelop as shown below—

HREF Ensemble mid-level cloud forecast for 1 PM Saturday looks similar to the NBM posted last night. The NAM-NEST and CMC GEM area similar, but have the area of cloudiness somewhat further south. Areas in Chester county and upper Montgomery county are forecast to be more sunny. (Click on image for larger view.)

Initial Post Discussion—[post_published]

As described earlier this week, a flat jet flow has prevented active weather from developing this past week and this upper air flow will continue into this weekend. Much of the low pressure development is in Canada. Things look to change next week.

A frontal boundary stalled to our south will allow for weak low pressure to develop Friday night.

Saturday

A few sprinkles may develop and end before daybreak Saturday.

The low will move off to our south and east, but moisture will remain in the form of mid-level cloudiness through much of Saturday.

NBM Cloud forecast for Saturday 1 PM (Click on image for a larger view.)

Not all models are on-board with this cloudiness Saturday (several models have over-forecast clouds recently) and this cloud forecast is lower confidence than usual. High temp 49.6º ± 1.4º (NBM) Blue Bell. (Seasonal average high is 46º-48º)

High pressure builds in and Sunday will be mostly sunny, but with some occasional clouds in the afternoon, especially west of the city.

High temp 46.9º ± 1.7º (NBM) Blue Bell.