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Sun 4:44PM Forecast Review — Well, we had little cloudiness, despite the GFS, HRRR and RAP model forecasts of cloud cover of 100%.

The NBM graphic I used with mean cloud cover captured it well.

In the fall of 2021, these models were upgraded with new cloud parameterization physics packages that have often over-forecast cloud cover. Until this issue is addressed, it’s something to keep in mind.

Sunday Forecast Update

Update Sat 03/18 @ 9:50 PM —We had more sunshine and less high, thin cloudiness from the city and westward Saturday than forecast.

Sunday starts sunny. There’s still uncertainty with the cloud cover early afternoon. Today’s GFS, HRRR and RAP still maintain a period of considerable low cloudiness Sunday from about noon until about 4 PM. More cloudiness northwest of the city. The HREF has minimal clouds.

There’s little disagreement about the very cold and the windy conditions for Sunday.

The NBM shows the wide “spread” (uncertainty) in the cloudiness forecast—

Today’s NBM shows uncertainty (red-violet contours) in the forecast cloudiness extending into Philadelphia from the northwest in the early afternoon. The red-violet represent 30- 40% cloud cover uncertainty. The models are split on this. I guess we’ll see.

Previously Posted Fri 5:22 PM —

A cold front will move through this evening (Friday). Some showers expected tonight about 10PM- midnight, with most of the activity just south of the city.

A second cold front will move through Saturday night and lingering upper air disturbance may affect us Sunday morning with clouds.

There’s uncertainty regarding the amount of cloud cover this weekend.

Average high temperature is 53-54º for the coming week.


Some cloudiness in the morning behind the departing cold front may last until noon. High pressure builds in for sunshine through high, thin cloudiness in the afternoon.

High temperature 50.1º sd 1.1º ( NBM model location- Blue Bell, PA)


Today’s GFS shows some upper air disturbance with moisture lingering Sunday morning. So some cloudiness is expected Sunday mid day. The NBM is more optimistic about sunshine for the day except areas far northwest of the city. It will be cold and windy.

High temperature 39.6º sd 2.4º ( NBM model location- Blue Bell, PA)

Today’s 19z NBM wind meteogram for location Wings Field Blue Bell PA (Click on image for a larger view.)


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Friday Forecast Update

Update Fri 03/17 @ 9:45 AM — This morning’s NBM keeps measurable precipitation (< 0.01″) in the Philadelphia area to a minimum during the daytime today. This is in keeping with previous forecasts. High temp 62º-65º

The latest HRRR does have some showers moving in, but during the evening hours, 9-11 PM.

Here’s the NBM—

Latest 12z NBM forecast total measurable precipitation Friday and Friday night. (Click on image for a larger view.)

In contrast, the latest HRRR has showers moving through 9-11 PM tonight—

Today’s 12z HRRR forecast for 11 PM Friday night. (Click on image for a larger view.)

Friday Forecast Update

Update Thu 03/16 @ 5:09 PM — Yesterday’s forecast for Friday had the line of showers dissipating before reaching the immediate Philadelphia area.

Today’s model forecasts suggest the showers make it into Philadelphia with reduced intensity— light scattered showers mid afternoon and early evening.

Friday: Some clouds and sun before noon, then increasingly cloudy with occasional bright skies into mid afternoon. Light showers move in from the west. Since there’s a range of model forecasts, I’ll turn it over to the NBM to do the heavy lifting—

Today’s 19z NBM 1 hour accumulated rain forecast for 3 PM Friday. It should be noted that the showers will likely be more spotty than suggested by this graphic. (Click on image for a larger view.)

Thursday and Friday Forecast

Update Wed 03/15 @ 5:18 PM — We’ll have a bit of high cloudiness Thursday morning which will dissipate for sunshine the remainder of Thursday.

A warm front followed by a cold front expected to bring clouds Friday and mild temperatures. The latest models have little in the way of rain Friday and Friday night, as a cold front will have its energy move to our north while a secondary low develops and moves off to our south. Much of the rain misses us.

ECMWF shows much of the rain dissipating as it moves towards Philadelphia Friday and Friday night. Little in the way of rain here.

Previously Posted Tue 4:48 PM —

Wednesday Forecast

The snow showers and the winds did not disappoint today. I thought the models did pretty good with this storm.

The cyclonic flow around the deep low off the New England coast will still be with us, as will the tight pressure gradient as high pressure builds in.

As a result, the winds on Wednesday will still be formidable and gusty, but should begin to subside Wednesday night.

Here’s the wind meteogram for Wings Field, Blue Bell for the next three days—

Today’s 19z NBM model Wind meteogram for location Blue Bell – Wings Field. Some wind gusts still in the 30-40+ mph range on Wednesday (Click on image for a larger view.)

Wednesday— The models are predicting sunny skies after some very early morning cloudiness. Highs 47º-48º

Thursday– sunny and milder. High near 57º Some clouds move in late in the afternoon.

Friday— Cloudy mild. Increasing winds. High near 60º Rain moves in during the early to mid afternoon ahead of a cold front.

Weather… and Other Things 'Up in the Air'

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