Tag Archives: Philadelphia area Weather Forecast


Not so sure we’re going to hit 70 ° on Sunday.

Fri 10 PM Update – No significant changes. I want to emphasize the winds both Saturday and Sunday will be 15-20 mph with gusts.

The very warm temperatures predicted for this weekend have been well-advertised.   The current EKDMOS  (Ensemble Kernel Density Model Output Statistics) shows very warm temperatures: 67º for Saturday and 68º for Sunday (Blue Bell)—

O EKDMOS High Temp Forecast for Blue Bell, PA

A strong southwesterly flow of warm air ahead of an approaching cold front will bring the unseasonably mild air.   But it won’t be a blue-sky day.  With the warmth will be considerable cloudiness and some uncertainty about the amount and timing of sunshine (if any).  It will be somewhat windy.

For Saturday, depending upon the model, we have sunny skies in the morning, becoming cloudy (NAM)

or clouds early breaking for sunny skies by noon (HIRESW-ARW) then cloudy later,

or mostly cloudy all day (GFS)!

For good measure, the NAM-NEST has some widely scattered showers in the morning (not supported by the other models).

So the warmth is a certainty, the cloud cover less so.   I’m leaning toward the HIRES-ARW with clouds breaking for some sun mid-day, then clouds return.—

HIRESW-ARW-MEM2 Cloud cover forecast 1 PM Saturday.  After 1 PM, clouds start move back in. Click for larger image.

The cold front moves through Saturday night.  There may be a spotty shower early evening, then heavier rain after midnight.

For Sunday, all models have the front moving through about 7 AM with clearing afterwards.   Mostly sunny skies but windy.  High temps near 70, but that will be late morning.   Temperatures slowly fall during the afternoon.

I don’t expect any changes, but I’ll do an update later if there are,  based on the new model runs.


[su_note note_color=”#defcdc”]Mon 6 PM Update: Today’s model runs continue with the forecast that the low pressure system’s precipitation shield will stay mostly east of Philadelphia. Little if any precip expected west of the Delaware river.

Mon 7:12 PM Update:  I just checked the latest GFS model run from 1 PM.  It has expanded the precipitation into the Philadelphia area and is showing 1.3 inches of snow by 8 PM.  None of the higher resolution models support this. I will update later this evening with this evening’s model runs.  The new GFS  will be available about 10:45 PM.  


…from this morning—

There has been a consistent forecast for a low pressure system to move to and develop along the coastline near NJ with the current time frame being Tuesday afternoon and evening.  The track and amounts of snow/rain have clarified in the past day.

The (new) GFS has been the most consistent with this forecast track and intensity— the low develops late in the process and moves mostly eastward rather than up the coastline.

Last night’s 1AM (06 UTC)  run of the GFS captures the event with accumulating precipitation barely making it into Philadelphia —

GFS Precipitation forecast 4:30 PM Tuesday

The other models, (NAM, CMC GDPS, ECMWF, etc) have joined in with the GFS forecast track and show similar precipitation coverage and amounts.

Some wet snow showers or flurries possible in Philadelphia and just north and west. Some of the models forecast a light coating of snow (< 0.5 inches) in central and eastern NJ.


Yesterday’s cloud base did lift and thin, but we never saw the degree of clearing that was forecast by the HRRR or NAM-NEST models. Showers moved in, as expected, about 5 PM, but the northern-most extent and their duration into the evening hours was greater than predicted by any model.

For today, (similar to last Sunday), several upper air disturbances are causing the cloud deck right now.  Sun should break out later this morning, but another upper air disturbance is expected about 4 PM (not talking about the Eagles here.)  So, another period of cloudiness possible later.

The coastal storm for mid-week mentioned in last Friday’s post remains difficult to forecast.  The NAM and Canadian GDPS have 1-2 inches of snow (less in the city) late Tuesday afternoon into evening.  The GFS shows less development and a coating at most. The GFS has done the best this season with these storms.  This storm is still beyond the range of the shorter range models.  Stay tuned.


[su_note note_color=”#defcdc”] Update 10 AM: I just downloaded the new HIRESW NMMB2 and HIRESW ARW2  (yes, so many  models, so little time.)  They are a little less optimistic about clearing.  At best, patchy clearing with highly scattered sprinkles possible, increasing about 4-5 PM.

HIRESW NMMB2      2 PM Simulated Radar and cloud cover

Well, we’re going to get a bike ride in, I hope.


…from earlier—

The low clouds and widely scattered showers were expected this morning.

I just downloaded the very latest NAMNEST, HRRR and RAP model data.

All models have winds shifting to the west about 11-12:30 PM, bringing in some drier air.  The HRRR is most optimistic about seeing some sun and bright skies by 12-2 PM.  The NAM NEST also has brightening skies by 2 PM, although not as clear as the HRRR.

I’m using the (sometimes unreliable) built-in cloud parameters, but clearing also supported by looking at the humidity fields.

HRRR cloud forecast 2 PM  (Arrow shows clearing skies)
NAMNEST Cloud Forecast 2 PM  Arrow points to few clouds.
NAM 3-D humidity below 70% (grey, not blue here!) shows areas of clearing.

The models maintain an increased chance of showers again about 4-7 PM as the main front moves through and again this evening.

We’ll see if the patchy clearing occurs as predicted.


[su_note note_color=”#defcdc”] Update Fri 10 PM: After reviewing this evening’s NAM, NBM and Hi Resolution model data, the gist of the forecast below still stands. The rain tapers and ends mid morning Saturday but it will remain unsettled.  Cloudiness lingers, and breaks in the clouds, bright patches, even some sun is possible.  Widely scattered sprinkles/showers remain possible as well and increase in likelihood again for a short period around 4 PM, as the main front moves through. Temperatures reach a high of about 58º around noon and slowly fall during the afternoon and especially after the frontal passage.

Sunday’s forecast below also remains intact. High 46º.  There’s a chance of an upper air impulse bringing sprinkles or flurries after midnight.[/su_note]

…. from Fri morning:

Low pressure will gradually move over us on Saturday and depart on Sunday.

Despite the location of the center of the low being directly over us, the rain will be will not be continuous.  It will become spotty.

Current NBM model forecast 1 Hour mean rain 1 PM Saturday. Click for larger image.

For Saturday, most models have rain moving through in the morning and to the north of us by afternoon.  Any rain lingering will be light and widely scattered.  The NBM 1 hour mean rain depiction for 1 PM Saturday gives a better picture.  There may even be some “dry slotting” in the afternoon, allowing brighter skies.   High 58º!

A weak cold front moves through during the mid to late afternoon Saturday. There may be another burst of showers and it will become windy.

For Sunday, mostly sunny skies, windy and colder with above average seasonable highs of 46º.  Winds diminish somewhat during the evening.

[su_note note_color=”#defcdc”] Next Week:  Of interest is a dip in the jet stream on Tuesday into Wednesday with the spawning of a coastal low.  There appears to be a shortage of cold air needed to make this a snow storm here, but this needs to be watched.

Canadian GDPS forecast for about midnight Tuesday-Wednesday.  North and west of red line is likely snow line.  White line is 32º surface temp line.