Category Archives: Weather Updates


Following the frontal passage that occurred on schedule Saturday afternoon, we didn’t get the clearing that had been forecast. A northeasterly wind flow behind the front will bring much chillier temperatures to our area on Sunday.

An area of rain associated with low pressure in the southeast will advance into our area on Sunday. There has been uncertainty about how fast these showers will move in, but the general time frame is between noon and 4 PM. Overall, Sunday will be quite autumnal, perhaps a taste of November in October.


  • Possibly some sun early, then becoming cloudy by late morning
  • Light showers possible as early as noontime but likely 2- 4 PM
  • Rain during the evening until midnight. Total precip 0.4 inches
  • High temp 50.5 sd 3.5º (NBM model-Blue Bell area)
  • NE winds 5-14 mph

Note that the NBM mean temperature’s sd (standard deviation) is very large.  Be advised that several models have high temperatures only in the upper 40s!


An interesting weather week coming up, as a tropical system will move into the Louisiana area and merge with a strong non-tropical low pressure system in the Midwest.  This will affect us later in the week, likely Thursday into Friday.

GEFS Model Forecast Wed 11 AM (Click on image for a larger view.)


The models overstated the cloudiness for this afternoon big time. A beautiful afternoon. I guess there was a good reason the NBM showed such high uncertainty.

While there had been uncertainty about the cloud forecast for this afternoon, the latest models show significant cloudiness this afternoon and the NAM-NEST, HIRESW and NBM show the possibility of scattered light sprinkles moving in about 2 PM from the east.


This morning’s low temperatures at 7 AM, based on the RTMA (Real Time Mesoscale Analysis)

RTMA  temperatures at 7 AM Sunday morning (Click on image for a larger view.)

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)

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.