Monthly Archives: April 2021

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

Updated Fri 10 PM highlighted below
Updated Sunday Forecast at Sat 10:45 PM highlighted

High pressure that brought sunny weather for Friday will linger long enough to keep Saturday dry before low pressure moves just south of our area Saturday night.

The latest GFS has the heaviest rain passing just to the south of Philadelphia with less than 0.5″ falling. The higher resolution models (HREF) still forecast fairly heavy rain (>1′) for the most of our area.

There’s still uncertainty with the time of clearing on Sunday, but the trend has been for clearing to occur somewhat later Sunday morning or early afternoon. I expect to have to update this forecast. Stay tuned.

Saturday

Moisture ahead of the low pressure system will first appear early with sunshine through a layer of high clouds that will thicken by early afternoon. Mostly cloudy conditions are expected by 3-4 PM. Tonight’s models have moved the clouds to 4-6 PM. Light winds. Saturday high temp 68.7º sd 1.6º

GFS advancing cloud cover northward (high-> middle-> low clouds by color)  by 3 PM Saturday with Simulated Radar showing rain in Virginia  (Click on image for a larger view.)

Rain begins as early as 6-8 PM Saturday evening (HIRES) models and closer to 11 PM (GFS model). Tonight’s models have the rain starting later, closer to the GFS forecast.

Sunday

Update : The models continue with rain ending 8-10 AM Sunday. Lingering cloudiness late morning. Considerable cloudiness Sunday afternoon with breaks of sun. A chance of widely scattered sprinkles mid to late afternoon as a weak trough moves through.

Rain tapers off by 10 AM although some models maintain the chance of a light scattered sprinkle between 10 and 12 noon. Instability cloudiness with breaks of sunshine in the afternoon. Windy. High 66.7º sd 4.0º (high spread/uncertainty!)

Wind Forecast

Wind Meteogram  NBM model,  Blue Bell  (Click on image for a larger view.)

 

Philadelphia Weather Outlook

WEEKEND WEATHER FORECAST PREVIEW

Update Thurs 8 PM highlighted below
Update Fri 11:30 AM highlighted below

High pressure that brought in the chilly weather for Thursday will be well off the coast by Saturday.

Low pressure advancing towards us will develop as it moves in our direction. Depending upon the model, it will be right over us or just to our south Saturday night.

GFS Model Surface Forecast Sunday at 2 AM  (Click on image for a larger view.)

Saturday

A return flow of moisture ahead of this low pressure system will bring considerable cloudiness for Saturday, but no rain expected during the daytime.

Update: Saturday will be sunny in the morning, then thickening high clouds. Mostly cloudy by about 3-4 PM Saturday.

Rain should develop Saturday evening. Rain starts about 6-8 PM. Fairly heavy rain at night. Rain starts about 9-11 PM. Total amounts have decreased to about 0.6-0.9 inches of rain.

There are some differences between the Canadian and US models, but the US models have been consistent that we get about 0.75 + inches of rain Saturday night. (The Canadian GDPS has less development and much less rain.) High about 68º NBM Blue Bell with low spread (uncertainty) of 0.8º

Sunday

The big question is how much development, how quickly the storm leaves and how much of an increase in its size due to intensification on Sunday. The models have varied. The NAM has some clearing Sunday morning. The GFS, Canadian and Model Blend (NBM) have lingering showers and clouds into late morning or early afternoon.

Update: Most models are showing the rain ending in the early to mid morning Sunday with gradual clearing.

High about 65º NBM Blue Bell with moderate uncertainty of 2.8º Very Windy.

Wind Forecast

Windy on Saturday, Very Windy on Sunday  (Click on image for a larger view.)