WEEKEND WEATHER FORECAST

Last Updated

Sat Evening Update: Skies clear early Sunday morning, based on the latest models.

The forecast is little-changed from the forecast “outlook” I posted yesterday.

Friday’s easterly flow will shift to a southeasterly flow ahead of a warm front that attempts to move through Saturday.

Saturday will be quite cloudy; any showers are expected to hold off until Saturday evening and Saturday night.  High 76.

A weak cold front moves through late Saturday night or just before daybreak on Sunday accompanied by light showers.  The front slows as it passes through.

Most models have clearing early Sunday morning, but the latest NAM suggests that some cloudiness may linger into mid or late morning Sunday and longer at the shore.

Sunshine is expected by Sunday afternoon with high temperatures about 82.

Tropical Storm (#09) is expected to intensify off the Georgia/South Carolina coastline.   Most models have it blocked from moving north, up the coastline.  It may become a Category 1 Hurricane.

COAMPS-TC Experimental model Forecast and Track

Tropical storms seem to reduce the accuracy of the model forecasts.  We’ll see how it goes this weekend.

WEEKEND WEATHER OUTLOOK

High pressure will build in to our north Friday and an easterly flow will bring cool temperatures and a significant amount of cloudiness on Friday.

Even more cloudiness is expected on Saturday as the high pressure system moves off to our east and the winds become southeasterly ahead of a warm front.  Some showers, widely scattered, are possible on Saturday as well, although much of the area will be dry.

A weak cold front moves in later Saturday and Saturday night with some showers.  Another high pressure system moves in for Sunday bringing more sunshine, although there are model differences about the amount of clearing we get on Sunday.

Complicating the forecast  is another tropical system that may form near Florida over the weekend and follow a track somewhat similar to Dorian.  This system is not expected to intensify anywhere near the level of Dorian.  The model forecast reliability often seems to be negatively impacted  by a tropical system in the area.  Stay tuned.

WEEKEND WEATHER FORECAST

High pressure builds in for Saturday, following the exit of Dorian.  Saturday will be mostly sunny, but some fair weather cumulus is expected in the afternoon.  High 79.

Sunday will be influenced by the same high pressure, but an upper air disturbance is forecast to move through late morning into the afternoon, bringing some mid to high level cloudiness.  High 78.

TODAY’S UNEXPECTED RAIN IN PHILADELPHIA

I find it fascinating that most of today’s models didn’t predict the rain that developed in a narrow, persistent band over Philadelphia. Interestingly, little rain developed at the shore to this point.

Radar 4:30 PM Friday, courtesy of weathertap.com

Going back to last night’s models, the WRF-NMMB and to a lesser extent the WRF-ARW were the only models to predict this rain last night.   However, the same models run this morning didn’t show it as much and the GFS, NAM really were off about this.

The unexpected rain was the result of some vorticity and vertical lift in the mid levels of the atmosphere, captured on this afternoon’s 2PM RAP model analysis—

RAP Model 2 PM Friday Analysis showing lift and vorticity at the 500 mb level (~18,000 feet)

I don’t know why, but as I mentioned last week, hurricanes seem to throw off the model forecasts, often in big ways.

This rain is expected to clear out later today.  The weekend looks to be beautiful with sunny skies and comfortable temperatures in the 70s.  I’ll do a brief update later this evening.

 

Storm Forecasts & Other Things "up in the air".