WEEKEND WEATHER FORECAST

Sat 04:50 PM Update — Looking over more advanced models than the NAM and NAM-NEST, the consensus is that it will be too warm for freezing rain in the immediate Philadelphia area tomorrow morning, nor is precipitation expected to change back to snow before ending Sunday evening. (Areas north of Allentown may see some snow.)   Rain will start 7-9 AM Sunday morning and will end in the evening.  (The new GFS v 16 still shows a chance of snow as the precip starts at 7 AM, then a quick change to rain.  See second graphic.  Possibly a ‘cold bias’.   We’ll find out.)

HIRESW-FV3 (Pre-release) Precipitation Type 9 AM Sunday (Click on image for a larger view.)

 

New GFS v16 still shows snow at 7 AM Sunday, then a quick change to rain..  Probably a “cold bias’ in the model.   I guess we’ll see tomorrow morning.

Sat 09:38 AM Update — This morning’s models show the following

  • Saturday— Clouds move in around noontime Saturday.
  • For Sunday, precipitation starts between 7 and 8 AM with some areas north and west of the city getting freezing rain to start, then a change to rain.
    NAMNEST 8 AM Sunday RED=Freezing rain   White line 32º (Click on image for a larger view.)


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Our area saw rain today, on schedule between 12- 3 PM, although some areas far to the west and north had a wintry mix, as temperatures remained below freezing. The mix did not occur as close to PHL as forecast.    Here’s the surface temperatures at 3 PM today—

RTMA (real time) Temperatures 3 PM Friday  (Click on image for a larger view.)

For the weekend—

Saturday,  a strong flow of relatively mild air moves in.  Original forecasts showed significant sunshine for Saturday, but the latest GFS suggests considerable cloudiness, a period of sun mid to late morning, then  a mix of clouds and sun at times in the afternoon.  There’s high uncertainty about the cloud cover Saturday, as captured in this NBM graphic—

NBM cloud cover standard deviation -spread or uncertainty- is high just north of Philadelphia (Saturday 5 PM)

With more clouds forecast, the high temperature looks to be 51.4º (NBM) and 49º (GFS) (Seasonal average high is 40º)

Saturday—

  • Considerable cloudiness, a period of sun mid to late morning, then  a mix of clouds and sun at times in the afternoon.
  • High temp 51.4º  sd 2.5º  (NBM model) Blue Bell (high spread!)  (Canadian models 53.4º)
  • Very WINDY winds from NW 15 mph, gusts to 30.

For Sunday, a secondary low forms off of Virginia. Precipitation moves in between 7 and 9 AM, starting as light snow or a rain mix. Changes to rain for most of the immediate PHL area. A change back to light snow is possible Sunday evening, with a coating at most.

NBM Snow totals Sunday evening. White line is the 1 inch line The immediate PHL has none or a coating at most.

(It appears that the new GFS may have a cold bias and the snow totals posted yesterday are incorrect and over-done.)

Any other winter, we’d have snow, but a lack of cold air to our north will keep it mostly rain.

Sunday—

  • Cloudy, starting as light snow or a rain mix. Changes to rain for most of the immediate PHL area. A change back to light snow is possible Sunday evening north and west, with a coating at most.
  • High temp 41.6.º  sd 1.4º(NBM model) Blue Bell area.
  • Winds NE 10-15 mph