Monthly Archives: December 2024

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Tuesday Morning – Light Snow Update

Posted Monday 12/23/24 @ 5:48 PM — Not much change with the latest models. Cold temperatures at the surface through 11 AM and “critical thickness” temperatures for snow are still forecast, although a change to sleet or freezing rain toward the end can’t be ruled out.

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. (Click on image for a larger view.)

Light snow start about 7 AM and tapers off by noon, as temperatures rise above freezing. The latest HRRR forecast for snow totals—

Today’s 18z HRRR. Yellow, red and magenta “thickness” lines are south of us at 11 AM, supporting snow as the precipitation type. Approxiimate snow totals are showin. (Click on image for a larger view.)
Light Snow Tuesday Morning

Posted Monday 12/23/24 @ 10:33 AM — This morning’s models continue with a forecast of light snow as a weak disturbance drops down from the northwest. The trend with some models has been for a more northern placement of the the light snow, while the higher resolution models continue to forecast a coating to 0.75 inches, with the upper range in the northern suburbs.

Light snow is expected around 7 AM and last through about 11 AM, as temperatures rise above freezing.

Here’s the latest HRRR—

Snow forecast based on the 12z HRRR (Click on image for a larger view.)

Originally Posted Sun @ 6:39 PM — —The current cold pattern will continue on Monday, but temperatures will slowly moderate through Christmas/Chanukah. as the current dip (trough) in the jet stream changes into a ridge—

NAEFS 200 mb winds (jet stream level) by Thursday showing developing ridge. (Click on image for a larger view.)

No major active systems are expected, but several models are showing some light snow or flurries Tuesday morning, mostly in northern sections—

Latest GFS shows areas to the north likely to see snow flurries or light snow. (Click on image for a larger view.)

It looks like it will be cold enough for snow and at most only 0.5″ is currently forecast in these northern sections. (It should be noted that the latest ECMWF has some light snow further south but the AI version of the ECMWF shows no snow at all on Tuesday.)

The rest of the week is uneventful, with a gradual warmup. A system may bring rain the end of next weekend, possibly lasting through New Years Day.

When it comes to weather, things can change, so stay tuned.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Posted Saturday 12/21/24 @ 11:14 AM — I’ve posted a second forecast review for yesterday’s snowfall.

Originally Posted Fri @ 10:40 PM — —A simple but cold forecast for this weekend. Low pressure in the Atlantic departs to our east and cold high pressure builds in with a highly amplified dip in the jet stream. No significant weather systems to affect our area through Christmas eve, although a weak system may affect far northern areas.

Graphcast GFS- AI forecast for Sunday 7 AM High pressure with a pronounced dip in the jet stream (Click on image for a larger view.)

Saturday Forecast

Cloudy early with sun breaking through late morning. A mix of sun and some extended periods of clouds during the afternoon. Windy. Gusts 25-30 mph
Wind chills in the low 20s at 3 PM.

NBM high temperatures: Blue Bell, PA 33º Philadelphia, PA 35º
Low uncertainty (based on standard deviation): ± 1.2º

Sunday Forecast

Sunny and very cold. Diminished wind gusts, still to 15 mph. Wind Chills during the day 13º.

NBM high temperatures: Blue Bell, PA 26º Philadelphia, PA 27º
Slight uncertainty (based on standard deviation): ± 2.0º
Temps drop below 10º Sunday night.