In yesterday’s forecast, I mentioned the possibility of cloudiness for Sunday afternoon.   Several of the models have low cloudiness moving in on an easterly flow Sunday afternoon.

The model blend statistical treatment shows about 40% mean (average) cloudiness, but the standard deviation (a measure of the spread in the models or it can be interpreted as uncertainty) is as high 45-50%, especially west of Philadelphia  Sunday afternoon by 3 PM.

NBM Cloudiness Standard deviation at 3 PM (Click on image for a larger view.)


The high resolution NAM-NEST shows low level cloudiness moving in, with a mix of high and middle level clouds further to our west—

NAM NEST cloud forecast (high, medium, low clouds) for 3 PM Sunday.   Low level clouds are in blue. (Click on image for a larger view.)

So, there’s uncertainty in the degree of cloudiness for Sunday afternoon, but I’m thinking it might be significant by 3 PM.

High temp Sunday 63.7º with a high confidence of 0.8º standard deviation. (The standard deviation can be thought of as 67% of the time, the temperature will fall with ± 0.8º of the mean temp 63.7º)


Low pressure is moving northeast off the coastline on Friday as high pressure builds in from the west.

A quick dip in the jet stream will occur tonight with some chilly temperatures by morning, as depicted by the “540 thickness line” (red line) in the SREF model—

SREF forecast for 8 AM Saturday  (Click on image for a larger view.)

Some chilly temperatures Saturday morning—

NBM low temps Saturday morning 8 AM  (Click on image for a larger view.)



  • Sunny
  • Starting from a low temperature of 37-43º,  the (NBM) high temp 58.3º sd 1.3º
  • Somewhat windy in the morning.
  • Winds NW 10-12   gusts to 15. Winds subside in the afternoon.

For Sunday, winds shift to the SSE and milder temperatures move in. Some high cloudiness expected too.


  • Mostly sunny.  Some high cloudiness possible in the afternoon.
  • High temp (Model Blend- NBM)  62.8º
  • Winds SE 10 mph, some gusts to 15 mph around noon.



Thursday 6:40 AM Update— All the models have clear skies by Saturday morning.

A strong cold front with a possible coastal low will move through Friday and clear the coastline by Saturday morning. Following the rain on Friday, the weekend looks good.

The Canadian model is somewhat faster with the front moving through than the GFS and  NBM (model blend). Even the models that show a slower movement of the front have the clouds clearing by mid morning Saturday.

The latest SREF model prolongs the rain and has slower clearing on Saturday. So a bit more uncertainty about Saturday’s forecast.

Here’s the current Canadian CMC Global model forecast for Saturday morning showing a high pressure building in from the northwest—

CMC GDPS forecast Saturday 5 AM   (Click on image for a larger view.)

Saturday should be mostly sunny and windy in the morning.  High temps near 57º, so it will be somewhat cool, especially with the windy conditions.

Sunday should be sunny, milder and less windy with high temps in the low 60s.

We’ll see if things progress as currently forecast.

The models over-predicted the rain totals by about 1-1.5 inches.

The latest Model Blend  (NBM) rain forecast for tonight through Monday night for the Philadelphia area showing  2.0 – 3.5 inches of rain, especially east into NJ—

NBM accumulated rain forecast (Click on image for a larger view.)

Heaviest rain will be Monday morning, but rain should persist through the day into the evening. Wind gusts 35-40 mph possible.

Weather… and other things "up in the air"