Philadelphia Area Weather Forecasts

MEMORIAL DAY WEEKEND WEATHER

Updated Friday 9:25 PM highlighted below

The forecast trend towards a cloudy, rainy and somewhat chilly Memorial Day Weekend continues. The only bright spot, literally and figuratively, will be Monday.

The current forecast weather setup, first took shape with Wednesday morning’s models. The ICON model was one of the first to pick up on the heavy rain.

An upper air trough develops over our area Friday through Saturday and lifts out by Monday. The upper trough will pinch into a closed low. Unfortunately, this upper air closed low will be far to our west, putting us in what’s called the “right entrance region” of a strong jet streak on Saturday.

Here’s the current (Friday morning) radar/water-vapor and RAP model jet stream flow showing the developing upper low—

By Saturday, this is the GFS forecast showing the upper low and jet streak entrance region—

GFS Model 250 mb level jet forecast 2 PM Saturday.  Note the position of the cold upper air low puts us directly in what’s called the “right entrance region of the jet streak”  (The red circles in the entrance region box are areas of strong vertical motion (vorticity) at the jet level.)  The southerly flow and orientation of the jet brings in moisture.  The vertical motion causes the rain.   (Click on image for a larger view.)

A strong moisture flow aloft will result in heavy rain. The latest GFS and NBM have joined the heavy rain forecast of the ICON model. Anywhere from 1.5 – 2 inches of rain now forecast from Friday afternoon through Saturday afternoon.

By Sunday morning, the same upper air low will induce the formation of a coastal low resulting in additional light rain, especially Sunday afternoon and evening and especially towards the coast.

GFS surface and 500 mb forecast showing upper low and coastal surface low.  More clouds and rain.(Click on image for a larger view.)

Memorial Day Weekend Forecast Details

Friday

Showers may start as early as noon- 2PM Friday, but the heavier rain moves in 3-6 PM Friday. 

Saturday

Cloudy with rain early, then intermittent showers. There may be some breaks in the rain at times. It will be chilly with a northeasterly wind. High 54.6º sd 4.2º (NBM Blue Bell)

Sunday

Cloudy with rain. The models are suggesting more rain over the entire area for much of the day on Sunday with the coastal low closer to the coast. An increasing chance of light Rain into the afternoon and evening, especially east into NJ. High 59.2º sd 4.6º (NBM Blue Bell)

Monday

The upper low moves out along with the coastal low Sunday, after midnight, allowing clearing.   Partly  sunny, some clouds .  Milder, but still cool for May. High 72.9º sd 1.8º  (NBM Blue Bell)

(The Canadian and ICON models  forecast slower clearing with considerable cloudiness lingering on Monday )

Wind Forecast
NBM model Wind/Gust forecast (Click on image for a larger view.)