Updated Fri 11:15 PM — Forecast from earlier still holds. Here’s the latest simulated radar depiction from the HIRESW NMMB2 showing rain exiting at 2 pm Saturday:
HIRESW NMMB2 model Simulated Radar 2PM Saturday
The latest models have come in and heavy rain is still forecast for the Philadelphia area. Depending upon the model, anywhere from 1.5-2.0 inches of rain will fall over most of the area between 7 AM and 2-4 PM!
But there are changes— the models have the rain ending between 2 and 4 PM on Saturday. There may be some clearing skies very late in the afternoon. (Previously, the rain was expected to end later.) It will be mild on Saturday, with high temps near 57º!
Sunday will be sunny in the morning, with cloudiness moving in during the mid afternoon as an upper air disturbance rolls through. It will be mild for January, with high temps near 49º.
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.
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.
…. 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.
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.
Update Fri 11 PM: Tonight’s NAM and GFS have moved the rain start time to 3- 6 PM on Sunday.
An upper air ridge will continue to bring us mild temperatures. The upper ridge will break down as low pressure approaches and moves up through the Great Lakes from Sunday into Monday. A secondary coastal low will develop on Monday
Saturday will be sunny in the morning, but throughout the day, high cirrus clouds will increase in sky coverage. High 54. Light winds.
Low pressure will gradually affect our weather on Sunday. Sunday will be cloudy and increasingly windy. As discussed in previous posts, rain should hold off until late afternoon and evening. (5-7 PM). High 52.
The rain should become heavy late Sunday night and continue into Monday. Monday was expected to be very warm with temps near 60º, but the models are suggesting a coastal low formation which may bring winds in from the northeast, lowering the high temperatures.
