Friday & Weekend Outlook

Updated Thu 10:34 PM — The forecast continues to evolve for the weekend. First, an upper air wave moving through on Friday will trigger showers and thunderstorms in far northwest areas mid Friday afternoon and these storms will move near the immediate PHL area late afternoon into the evening. Most but not all of the activity northwest of the city.

CAPE values are forecast to exceed 2200 j/kg, so strong storms are possible, but severe not expected.

The front sinks slowly through our area on Saturday. Strong storms and showers possible throughout the day, but late afternoon and evening are the most likely times.

Sunday and Monday are  looking better and better. Tomorrow’s Weekend Weather forecast will nail things down

Updated Thu 7:42 AM — The forecast for the weekend continues to improve, as the GFS now shows more spotty precip during the day and the heaviest rain during the evening hours. Most models show clearing by Sunday afternoon. Monday looks good.

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Updated Sat 10:35 PM — Current Sunday forecast looks good. High temps 90-92°, dew points low 60s. The approaching cold front won’t affect us until Monday morning.

Showers and thundershowers Monday morning and early afternoon with the cold front likely will not be severe in our area. Some areas of heavy rain possible.

The upper air low pressure system will finally move out allowing high pressure and an upper air ridge to move in bringing much warmer conditions, above seasonable average temperatures. (average highs are 83º Blue Bell and 85º Philadelphia)

Today’s 18z GEFS shows the upper ridge (1) the upper low (2) and a cold front moving towards us (3) late Sunday. By the end of the week, the typical Bermuda high pressure (4) will move into its usual position bringing more heat and humidity. (Click on image for a larger view.)

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Sunny and somewhat warmer. Lower dew points in the low 60s. High temperature 90.5º ± 3.5º NBM model, Blue Bell PA.

Today’s 19z NBM Model high temperatures Sunday. Black contours are 2 degree increments. (Click on image for a larger view.)

A cold front moves in late Sunday evening and overnight with showers and thunderstorms into Monday morning.


Updated Thu 10:35 PM — Tonight’s models have moved away from widely scattered showers for Friday. Additionally, they’ve moved away from Friday’s cloudiness as well. Looking at the humidity fields, I wouldn’t be surprised if there’s some periods of low clouds on Friday. I guess we’ll see.

Updated Thu 7:30 PM — Friday’s weather forecast will be interesting. Many models show sunshine and fair weather clouds. The higher resolution models show sunshine with periods of clouds and very widely scattered sprinkles from mid morning into the afternoon, especially northern areas.

Update Thu @ 11:40 AM — The moderate rainfall we’re getting Thursday morning will taper off about 2-3 PM Thursday afternoon. Clouds linger with a few very widely scattered showers.

Things improve considerably Friday through Sunday as the low pressure system that has been persistent will move away. High pressure will dominate through most of Sunday. A southwesterly flow of more summer-like air will move in.

GEFS (mode) forecast for 2 PM Sunday. Cold front in Ohio Valley moving eastward will arrive late Sunday or Monday. High pressure in western Atlantic (H) has replaced the upper low and will bring much warmer, summer-like temperatures.(Click on image for a larger view.)

Update Wed @ 7:58 PM — The most recent models show rain lingering into early Thursday afternoon before ending. We may see some light rain as late as 2-3 PM. Considerable lingering cloudiness. Some heavier rain expected in the morning Thursday; here’s the latest RAP model accumulated rain—

Today’s 21z RAP model accumulated rain forecast. (Click on image for a larger view.)

Updated Wed 6:02 PM — Current radar and water vapor imagery around 5:40 PM looks pretty close to the 06z HREF forecast (2 AM run) from this morning—

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No sign of the usual summertime Bermuda High effect; it’s well out to our east.

I expect changes in the forecast as the week unfolds. Much depends on the position of that upper low. Stay tuned.