Sunday and This Week’s Weather Outlook

Update Sun 12/04 @ 10:14 AM — Today will be mostly sunny. The ongoing forecast uncertainty about a period of cloudiness in the early afternoon still remains, as the HRRR and RAP show this cloudiness, the GFS and NAM do not. (The current versions of the HRRR and RAP have been overestimating cloud cover since their update last year.) Some high cirrus will also be visible in the southern parts of our region.

The weather for this week will be affected by a strong southwesterly jet flow aloft from the southern jet stream—

NAEFS mode shows strong southern jet stream (250 mb level winds) bringing moisture across the country. The red 540 thickness line can be seen as boundary between cold air northward and warm moist air southward. Areas of low pressure will develop along this boundary and affect our weather. (Click on image for a larger view.)

Rain will develop Tuesday into Wednesday and again Friday into Saturday.

NAEFS surface forecast for Wednesday at 1 PM. Notice the stream of low pressure systems moving into our area. (Click on image for a larger view.)

Laden with moisture from the Pacific, we’ll have several areas of low pressure form and affect us during the week.

BTW, for those following my postings from last week, I mentioned the possibility of a wintry mix on Friday. That speculation has fizzled out, as the boundary line between cold and warm air is now forecast to be north of our area.

Forecast Review: We had the sunshine about 3 PM and the cold front is coming through at 5 PM—

Forecast Update

Update Sat 12/03 @ 12:26 PM — This morning’s models are less clear-cut about any breaks of sun this afternoon. Still possible around 3 PM, according to the HRRR. Another line of showers about 5 PM.

For Sunday, once again the GFS has backed away from any instability cloudiness; the HRRR has some periods of clouds but not in all locations, so it looks like mostly sunny and cold for Sunday. Breezy but much less windy than Saturday.

Update Fri 12/02 @ 10:43 PM — Tonight’s models have clarified the earlier posted forecast for Saturday. Rain with the warm front moves through by 12-1 PM. The actual cold front moves through about 4-6 PM with additional showers.

Sunshine should break out for a period of time in the afternoon. It will be mild but very windy.

Here’s the latest HREF model forecast for 1 PM showing the back end of the rain moving into NJ—

Tonight’s 00z HREF simulated radar forecast for Saturday at 1 PM. Notice the break in the clouds after the rain moves east. (Click on image for a larger view.)

Previously Posted Fri 3:34 PM —

A warm front associated with deep low pressure in Canada will pass through our area on Saturday, followed by a cold front. Rain and very WINDY conditions will develop

High pressure builds in for Sunday.

This morning’s water vapor image shows both warm fronts and cold fronts associated with the low pressure system in Canada—


The warm front approaches about 7 AM-8 AM from the west with rain and very WINDY conditions. The GFS shows gusts to 50 mph (although we saw with a similar condition on Wednesday that wind gust forecasts can be an inexact science.) Rainfall is only expected to be about 0.35 inches. Warm temperatures on Saturday, but WINDY. Becoming colder in the late afternoon.

High temperature 57.6º sd 0.9º NBM model Blue Bell, PA

NBM Wind Meteogram for the weekend, for Blue Bell PA. High winds mid-day on Saturday following warm front. Cold front moves through about 5 PM.

The rain ends around noontime in the city and later in NJ. Considerable cloudiness is forecast for Saturday afternoon, although some breaks in the cloud cover are possible. The main cold front moves through about 5 PM with a quick shower or sprinkle, then temperatures drop.

The GFS shows the expected scenario well—

Today’s 12z GFS forecast for 1 PM Saturday. The bulk of the rain has moved into NJ. The main cold front in central PA will move into our area by 5 PM with some additional light showers. Cold windy conditions follow. (Click on image for a larger view.)


High pressure builds in for Sunday. Colder. Sunny in the morning. The models have been on and off with a potential upper air disturbance that may bring a period of clouds in the early afternoon Sunday (1 PM- 4 PM). The latest GFS shows this period of cloudiness again—

GFS relative humidity at levels for cloud formation along with contours of vorticity at 500 mb. (Click on image for a larger view.)

It should be noted that the NBM doesn’t show cloudiness for Sunday.

High temperature 43.3º sd 1.7º NBM model Blue Bell, PA