Daily Archives: Friday, December 27, 2024 11:03 pm

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx

Forecast Review

Sunday night’s actual rainfall was within the range of the model forecasts—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)
Forecast Update

Posted Sunday 12/29/24 @ 4:45 PM — Radar is beginning to pick up some light developing echos just to our south. The main area of rain will move in between 8 PM (western areas) and 9 PM (closer to the city).

4:40 PM Combined RADAR and MRMS with RAP Model Omega (vertical motion) yellow contours. (Click on image for a larger view.)

It has already gotten windy and winds will continue to increase this evening. Total rainfall will be somewhat less than predicted yesterday with totals in the 0.25-0.40″ range.

Sunday Forecast Update

Posted Sunday 12/29/24 @ 8:49 AM — Most areas have had less than an inch of rain over the past 48 hours, less than originally forecast—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Past 48 hours. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)

The 1 AM run of the NAM-NEST (06z) has joined the other models in predicting some bright skies and sunshine developing from east to west about 11 AM. It forecasts only 2 hours of these bright conditions before lower clouds move in. The latest HRRR (12z) still maintains bright skies and even some sun for much of the afternoon.

The HRRR has showers moving in from the west about 9 PM with some widely scattered activity a few hours earlier, about 7 PM. The total additional rainfall forecast has been downgraded to ad additional 0.5″ Sunday night.

Sunday Forecast Update

Posted Saturday 12/28/24 @ 9:52 PM — Here are the salient points about the Sunday’s weather forecast—

  • Low clouds and drizzle persist through much of the morning.
  • Precipitation ends by noon.
  • Most models have breaks of sunshine and no rain in the afternoon.
  • Increasingly windy in the afternoon and evening
  • High temperatures in the low 60s
  • Rain moves in between 6 PM and 8:30 PM from the west
  • Rainfall may not be as heavy as originally forecast; about 0.5″ Sunday night.
Tonight’s HRRR model c;loud forecast for 3 PM Saturday Tan= thin high level cirrus clouds which often lets some sun filter through. Maroon=mid level clouds Blue= low level clouds (Click on image for a larger view.)

Of interest are today’s runs of the NAM-NEST which maintains low clouds and even some drizzle in the afternoon with scattered showers breaking out late afternoon. The latest model run, just available has the same forecast. This is an outlier forecast, but regular visitors here know my mantra, “Never ignore the NAM”. So I guess we’ll see what happens.
Go Eagles!

Saturday Forecast Update

Posted Saturday 12/28/24 @ 10:02 AM — The rain moved in and will remain with us for much of the day. Current RAP model analysis shows minor areas of upward vertical motion that will move in our direction during the day and night time hours—

RAP model analysis of vertical motion (Omega) shows areas of upward motion (yellow L) that will move towards us with additional periods of rain. The rain moves in the direction of the green contour arrows. (Click on image for a larger view.)

For Sunday, a system is developing along an inflection area of the jet stream along the Gulf Coast. This will move towards us bringing rain Sunday night into early Monday—

Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. Developing Low pressure in Texas will move towards us and arrive late Sunday into Monday. (Click on image for a larger view.)

The GFS is still showing a pause in the rain for Sunday afternoon and even some sun in Philadelphia and areas eastward, but the latest NAM-NEST model shows some lingering light drizzle and sprinkles in the city during the game. I’m leaning towards the more optimistic GFS forecast at this time for the Eagles game. Heavy rain expected Sunday evening and night beginning about 7-8 PM from west to east.

Previously Posted Fri @ 11:03 PM — —Two low pressure systems will affect our weather this weekend. The first will last through much of Saturday. Luckily, the second system, as forecast with prior updates Thursday and Friday, will remain to our west for the afternoon on Sunday. The Eagles game should be mostly dry with even some breaks of sun.

Rain begins here around midnight (Friday).

GFS forecast for 1 PM Saturday. Rain for much of the area. (Click on image for a larger view.)

Saturday Forecast

Rain for much of the day, tapering off towards evening, except continuing in South Jersey.

NBM high temperatures: Blue Bell, PA 48º Philadelphia, PA 51º
Average uncertainty (based on standard deviation): ± 1.4º

Sunday Forecast

Clouds lift for some bright spots and even some sun (especially in NJ) Rain moves in about 6 PM and continues heavy at times through the night. Increasingly windy and gusty during the afternoon and night time hours.

NBM high temperatures: Blue Bell, PA 62º Philadelphia, PA 64º
Slightly above average uncertainty (based on standard deviation): ± 2º

GFS forecast for Sunday 7 PM. Rain moves in from the west (Click on image for a larger view.)