Category Archives: Philadelphia Area Weather Forecasts

Philadelphia Area Weather Forecasts

FIRST POSSIBILITY OF SNOW HERE?

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Chance of Snow Fades Again

Update Sat 02/04 @ 3:42 PM — The latest run of the ECMWF has backed away from the potential snow and is more in line with the other ensemble models. There are still huge timing issues between today’s GFS, the Canadian and ECMWF, so uncertainty remains high. However the likelihood of a coastal snowstorm has become unlikely now. That snow possibility didn’t last long.

First, an observation. Today’s adjusted mean sea level pressure was 30.68″. For you barometers fans, that doesn’t happen here very often. (Average sea level pressure is 29.92″ and typical barometric pressures with sunny cold weather is in the 30.25″- 30.35″ range.) Readings above 30.60 are the result of very cold, dense air, something that should be no surprise if you’ve stepped outdoors today.

Possible Snow

There haven’t been many (maybe any) possibilities of snow this winter season. A few marginal possibilities on the extended forecast models all have fizzled out. A possibility has begun showing for next Friday through Sunday time frame.

The global models forecasts extend out to 384 hours (15.5 days) but you don’t have to be a meteorologist to know that forecasts beyond 3-4 days have increasing uncertainty. Once you get into the 5+ day range, meteorologists primarily use “ensemble” models, models that try to statistically account for modelling error, input data errors, model biases, and chaotic effects.

Today’s GFS and GEFS (ensemble) and Canadian Ensemble (GEPS) along with the ECMWF are suggesting the formation of a coastal low the end of next week. A giveaway of the uncertainty with this potential system is the wide range in the timing, from late Friday night to late Saturday night.

Here’s the ECMWF for next Saturday night—

00z ECMWF forecast for Sunday at 1 AM shows coastal low, cold air and deep dip in the jet stream (as captured by the red 540 thickness line) (Click on image for a larger view.)

The NAEFS which combines the GEFS and the Canadian GEPS (ensembles) has different timing and somewhat warmer forecast—

Todays 06z NAEFS forecast for 7 AM Saturday shows wraparound moisture with 32º line(white) just through Philadelphia. This is a rain to snow event, according to this model that occurs almost 20 hours sooner. (Click on image for a larger view.)

So for you people wondering about possible snow here, this setup is as close as we’ve seen forecast-wise this season. BUT the difference in timing suggests terribly high uncertainty and the possibility that this snow forecast fizzles out is well above average. If you like snow, don’t get your hopes up quite yet.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Update Sat 2/04 8:26 AM — Last night’s models have backed away from the forecast of “considerable cloudiness” on Sunday. It looks like Sunday will be sunny in the morning, increasing thin, high level cloudiness in the afternoon. Still windy. High 47º sd 1.9º. Blue Bell.

The well-advertised drop in the temperatures occurred today and tonight’s wind chills will be even a bit lower than forecast yesterday, according to the latest NBM—

Today’s 19z NBM model wind chill forecast for 1 AM tonight (Friday) (Click on image for a larger view.)

Current mid level water vapor satellite image shows the cold air over the our area and several disturbances in the West that are forecast to drop to the south of us.

Disturbance in the Western US will drop south of us. A coastal storm will form off of the southeast coast, but move out to sea. (Click on image for a larger view.)

Here’s the latest NAEFS corresponding to the above water vapor image. The strong high pressure over Illinois combined with the deep low over eastern Quebec provinc is setting up a strong pressure gradient, causing our high winds.

NAEFS showing the detail of the above water vapor image. Very cold high pressure is moving down over us. Deep low pressure over eastern Quebec province. (Click on image for a larger view.)

Winds will gradually reduce over the weekend and temperatures will moderate. The high pressure system moves off and low pressure develops off the southeast coast on Sunday.

Saturday

Sunny, less windy. Cold

High temperature 26.7º sd 1.7º ( NBM model location- Blue Bell, PA)

Sunday

Considerable high and mid-level cloudiness develops as moisture returns aloft and a southerly flow develops. Much milder, but it will be WINDY.

High temperature 47.0º sd 1.9º ( NBM model location – Blue Bell, PA)

Looking Ahead

A weak front comes through on Tuesday. A strong storm affects us sometime Thursday into Friday; it will be rain in our area. No snowstorms for us showing on the models.