Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Sun 9:36 AM Forecast Review — The total rainfall yesterday fell short of several model forecasts in most areas. The system, originally expected to linger into Sunday, cleared out before daybreak, reducing totals. Retrospectively, the GEFS and NAEFS ensemble models had more accurately forecast the rain totals. Here’s the MRMS rain gauge and radar estimate for total rainfall yesterday—

MRMS rain guage – radar based estimate of rainfall received. Colors are in inches. Green contours are in mm (25.4 mm= 1 inch) (Click on image for a larger view.)

The forecast update posted last night still holds. Sunshine, with instability cloudiness expected this afternoon.

Sunday Forecast Update

Updated Sat 10/14 @ 9:54 PM — Rain will be ending about 3 AM and skies clear around sunrise. Mostly sunny in the morning, sun and periods of cloudiness in the afternoon due to instability.. Windy. Highs 59º Blue Bell, 61º Philadelphia.

Saturday Forecast Update

Updated Sat 10/14 @ 9:51 AM — Showers have moved through Philadelphia and a steadier rain is on the way by late morning.

The latest water vapor image shows the likely placement of the secondary low pressure expected to form off the coast—

Current Water Vapor (9:46 AM) image with superimposed RAP model thickness lines (yellow), potential vorticity (fine white contours) and superimposed MRMS radar. Notice the fine white contours of Potential Vorticity over the “black band” of the water vapor image in the red box. This is the likely location of the secondary low formation. (Click on image for a larger view.)

The latest NBM (12z) just available shows its latest estimate of total rainfall with this system —

Update Fri 10/13 9:49 PM — The earlier start of the rain Saturday, between 7 AM to 9 AM, is now forecast by additional models.

Previously Posted Fri 6:01 PM —

As forecast this past week in “This Week’s Weather”, a low pressure system will approach from the west early Saturday and a secondary coastal low will quickly develop along the coast later Saturday through Saturday night.

Here’s the ECMWF forecast for 2AM Sunday morning, showing the secondary coastal low—

ECMWF forecast for 2 AM Sunday morning (Click on image for a larger view.)

A generalized 1″-1.3″ rainfall is forecast for most of the area through early Sunday morning.

Saturday

Cloudy with rain moving in from the west anytime between 8 AM and noon.

(There’s been a wide spread of times for the rain to start here, depending upon the model. This afternoon’s high resolution models have closer to a noon start time. With this sort of thing, I tend to lean towards the GFS which has an 8-9 AM start. ) Increasingly windy.

High temperature 55º ( NBM model— location Blue Bell, PA)
High temperature 57º ( NBM model— location Philadelphia, PA)
uncertainty ± 2.3º

Sunday

Any remaining showers ends early morning. Clouds break for some sunshine 2-5 PM in many (but not all) areas. Windy.

High temperature 58º ( NBM model— location Blue Bell, PA)
High temperature 59º ( NBM model— location Philadelphia, PA)
uncertainty ± 1.8º

Winds
NBM Wind Meteogram for Blue Bell, PA (Click on image for a larger view.)