Category Archives: Philadelphia Area Weather Forecasts

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Phillywx #Philadelphia #weather #PAwx

Sun 5:21 PM Forecast Review — None of the model forecasts were stellar today. In a general way, the heaviest rainfall was to our north as expected, but heavier showers moved through during the afternoon. As mentioned, there was much greater than average “spread” (uncertainty) with today’s models, so the poor forecast performance wasn’t a surprise.
Sunday Forecast Update

Updated Sat 10/28 @ 6:06 PM —There’s still a wide range of model forecasts for the showers on Sunday. The current trend ( with the exception of the HREF model) is for very little in the way of rain here in the immediate Philadelphia area, as forecast by the HRDPS this morning (see graphic below on previous update.) I’m still leaning towards very little rainfall Sunday.

Capturing the great uncertainty and low confidence is the NBM model which still shows an incredibly large standard deviation of 6.0º in its forecast high temperature for Sunday. (Typical sd is about 0.8º -1.5º for a 24 hour forecast.)

Sunday Forecast Update

Updated Sat 10/28 @ 9:30 AM — Following some heavier showers at daybreak Sunday, it appears that most of the rain/showers will be north and west of the city. Only very light, occasional, scattered sprinkles possible for the rest of the daytime Sunday.

06z HRDPS shows extremely light sprinkles for much of the immediate Philadelphia area (following some heavier showers early morning) (Click on image for a larger view.)

Previously Posted Fri 8:14 PM —

Friday’s media forecasts of “sunny with highs near 80” didn’t jive with reality – the clouds, light sprinkles and cooler temperatures. Things continue to change and there’s a change in the forecast for Sunday. First let’s see where we are—

Currently, cold air is diving southward into the Rockies and some push eastward is occurring on a somewhat stationary cold front north of us—

Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine white contours) and superimposed MRMS radar.

The above water vapor image corresponds to this NAEFS weather map—

Friday afternoon’s NAEFS model depiction of current weather, corresponding to the water vapor imagery in the graphic above. (Click on image for a larger view.)

The question for the weekend forecast is how much push east and southward will the cold front to our northwest move?

Saturday

The models are still forecasting sunny skies and unseasonably warm temperatures. There seems to be a consensus on this. Some cloudiness may move in, especially north and west, late afternoon.

High temperature 81º ( NBM model— location Blue Bell, PA)
High temperature 82º ( NBM model— location Philadelphia, PA)
uncertainty – ± 1.4º

Sunday

The real question mark has been with Sunday’s forecast. Prior to today, it was felt that the showers associated with the front would stay to our north and west. That’s no longer the case.

Today’s models (with the exception of the Canadian HRDPS and RGEM) are forecasting low clouds, with showers as early as daybreak and light showers/rain throughout the day. But there’s higher than usual uncertainty. The temperature forecast standard deviation is 6.1º which is extraordinarily high; typical is 1º-2.5º and captures the low confidence in the current forecast.

Total rainfall is anywhere from 0″ to 0.5″

High temperature 62º ( NBM model— location Blue Bell, PA)
High temperature 65º ( NBM model— location Philadelphia, PA)
uncertainty – ± 6.1º

Sometimes, the best forecast is indicating that for Sunday, we just don’t know for sure.

I’ll update Saturday morning.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Phillywx #Philadelphia #weather #PAwx

Sunday Forecast Update

Update Sun 10/22 9:18 AM — The model guidance has backed off on the cloudiness today. Mostly sunny. Maybe some cloudiness towards sunset.

Updated Sat 10/21 @ 5:41 PM — The light showers that had been expected to move through Sunday morning will stay to our south—

Today’s 18z HRRR shows the clouds and rain to our south at 8 AM Sunday morning. Similar forecast with the HRDPS. (Click on image for a larger view.)

Periods of cloudiness and sunshine in the afternoon. Cooler on Sunday with highs 56º (Blue Bell) 58º (Philadelphia).

Saturday Weather Update

Updated Sat 10/21 @ 10:08 AM — The upper trough will swing through today. Disturbances (areas of vorticity and potential vorticity) will move through causing occasional cloudiness and even a few sprinkles this afternoon.

Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), potential vorticity (fine white contours) and superimposed MRMS radar. The upper trough (RED dashed line) will rotate through today. An weak low pressure system (L) is expected to move through Sunday morning with showers in the morning.

Clouds should thin for some sunshine about 11 AM, but periods of cloudiness will return mid afternoon. Some light sprinkles are possible in a few areas.

Previously Posted Fri 6:11 PM —

A low pressure system off of the New England coastline will move away as a cold front moves through tonight. Skies should partially clear Saturday, but a general cyclonic flow with embedded disturbances will affect us this weekend causing periods of cloudiness and a widely scattered light fast moving shower. It will be VERY WINDY.

The current water vapor image shows the line of showers ahead of the cold front that will move through this evening ( Friday), about 9 PM. Much of the heavier rain will move up to our northwest —

Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), potential vorticity (fine white contours) and superimposed MRMS radar. The white arrow shows the expected path towards us of a weak area of low pressure, now in Canada,

For Saturday—

Current Canadian RGEM forecast for Saturday at noon. Rain has departed, clouds and sun in our area. The low pressure system expected to move through Sunday morning is in Wisconsin. (Click on image for a larger view.)

Saturday

Clouds break for sunshine by 9 AM. It will become VERY WINDY with gusts exceeding 40 mph. Clouds move back in some areas, especially south of the city. Areas in Chester and Delaware counties may see some light, fast moving showers about 2 PM. Wind gusts near or above 40mph.

High temperature 63º ( NBM model— location Blue Bell, PA)
High temperature 64º ( NBM model— location Philadelphia, PA)
Low uncertainty of ± 0.7º

Sunday

Additional light showers may move through Sunday morning with another disturbance. Then a mix of clouds and sun in the afternoon. Continued windy.

High temperature 58º ( NBM model— location Blue Bell, PA)
High temperature 60º ( NBM model— location Philadelphia, PA)
Average uncertainty of ± 1.7º

Wind Meteogram
Today’s NBM 18z wind meteogram for Blue Bell, PA (Click on image for a larger view.)