Forecast Update

Update Wed 12/07 @ 8:22 PM — Latest GFS shows snow showers or flurries in our area after midnight Sunday into predawn Monday. No real accumulation expected except north of Allentown where it will be below 32º. The GFS model has a somewhat unusual looking forecast map, so I must confess that I have low confidence with its current forecast—

Forecast Updates

Update Wed 12/07 @ 5:43 PM — see Sunday update highlighted below with possible snow showers Sunday evening.

Update Wed 12/07 @ 10:12 AM — Drier air will be gradually entering our area Wednesday afternoon, but today’s models show no sunshine, as the clouds are expected to hang tight. Clouds begin to break early this evening, but fog may form again towards midnight.

For Thursday, partly sunny, some clouds.

For Friday, things have finally clarified. Becoming partly to mostly sunny. No wintry mix expected in the evening as the ECMWF forecast has joined with the GFS; the cold high pressure will nose out the moisture to our south, keeping us dry even through early Saturday.

For Saturday: mostly sunny. Increasing clouds in the late afternoon.

For Sunday: cloudy with rain most of the day. Update latest GFS and ECMWF show the possibility of light snow flurries or a coating Sunday night as low pressure develops off the coastline—

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Update Tue 12/06 @ 4:01 PM — The rain came in on schedule today, Tuesday. This weak but rainy system will exit Wednesday.

For Wednesday, we’ll be left with clouds, perhaps a few breaks of sun. High in the low 50s.

For Thursday, partly sunny. High in the low 50s.

For Friday, another system approaches from the southwest. High pressure with cold air aloft nosing down from the northeast will either (1) suppress the moisture to the south, keeping us dry or (2) introduce enough cold air to allow a wintry, non-accumulating wintry mix to fall after midnight Friday-Saturday in areas especially west of the city.

For Saturday, a northeast moist flow will send back a fair amount of cloudiness into our area.

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Update Mon 12/05 8:53 PM — Regular visitors to this site know that over the past week, I’ve been watching for the possibility of a wintry mix to develop sometime over the Friday to Saturday timeframe. I nixed that possibility in last night’s outlook, based on the GFS and NAEFS. Today’s ECMWF has resurrected that possibility. The models have unusually low agreement in their forecasts for for later in the week. I’ll keep an eye on it.

Previously Posted Mon 11:04 AM —

Overview

A flat to slight ridge jet stream will influence our weather this week—

The trend over the past few days is for the coldest air to remain further north of our area and for the flow to be more ridge-like with it just sinking southward by the weekend.

Moisture moving up from the southwest from the southern jet stream will bring a series of disturbances to our area with rain Tuesday into Wednesday and rain Friday into Saturday. With a flat to ridge-like jet flow, no major storms are forecast to develop, just these smaller disturbances.

By Saturday, the jet flow is flatter and further to our south, meaning colder air will move in——

From the above map, we can see that some waves (note the wavy red 540 thickness line) are beginning to develop in Wyoming and Utah. This is the early stage of a large storm that will develop and affect us and much of the country next week.

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—

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

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.

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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.

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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—

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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—

Saturday

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

Winds:

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—

Sunday

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—

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