HOT WEEKEND, HUMIDITY NOT TOO BAD

Fri 12:48 PM Update — Today’s models continue with the forecast of temperatures in the 90s (Saturday 93º) Sunday (96-97º) but dew points will slip back into the 50s for Saturday and mid 60s for Sunday during these peak temperatures in the afternoon hours. That’s different than what you’re hearing from the TV weather entertainers.

A weak frontal system will move through late Friday with some very light widely scattered showers preceding the frontal passage. A few areas might have a heavy thunderstorm.

As mentioned earlier in the week, we are transitioning from an upper air trough pattern to more of an upper air ridge pattern this weekend.  A Bermuda High will pump in hotter and more humid air. (The ridging predicted earlier in the week will be less pronounced than previously thought.)

SREF model forecast for Sunday 12 PM  (Click on image for a larger view.)

This afternoon’s models have continued to forecast  temperatures in the 90s for Saturday  (93º) and Sunday (96º) afternoon.  Here’s the current NAM temp forecast for Sunday—

NAM Sunday 3 PM Forecast High Temps  (Click on image for a larger view.)

At the maximum heat of the day, dew point temperatures above 70º will be south and west of the immediate PHL area.

So with the high July heat, there will be no corresponding increase in water vapor; relative humidity and dew points will correspondingly drop to the somewhat less oppressive 60s during the maximum heat of each afternoon in our immediate area—

NAM Forecast Dew Point Temperatures Sunday afternoon.   (Click on image for a larger view.)

Little or no chance of rain over the weekend.

As is often the case, dew points will increase at night, so it will be very humid during the evenings and night time hours.   Some fog is likely in NJ Saturday night and early Sunday morning.

WEATHER PATTERN CHANGE STARTING THIS WEEKEND

A weather pattern change is coming.  For the past two to three months, we’ve had a persistent weather pattern characterized by an upper air trough with the upper flow coming in from the northwest, as shown below (from June 24th).

GEFS forecast for fourth week in June

The usual “Bermuda High” that we always hear about in summer was nowhere to be found.

Starting this coming weekend, a more typical summertime pattern is forecast to develop with the upper trough we’ve had transitioning to an upper air ridge and a Bermuda High bringing a southwesterly flow of hot and humid air to our area.

GEFS forecast for this coming Sunday, showing an upper ridge and Bermuda High (Click on image for a larger view.)

Temperatures are expected to move from the current highs of the mid to upper 80s to much hotter high temperatures in the low to mid 90s with higher humidity.  (Current average high temp is 86º)

 

MORE SHOWERS ON SATURDAY

Sat 07:42 AM Update — The models are more optimistic about sunshine for Saturday. Still a good chance of showers and thunderstorms about 4-7 PM, but they will be scattered and not every area will get one.

Following a very rainy Friday from tropical storm Fay, we could all use some sunshine for the weekend.   It appears we may have to wait for Sunday for that really nice weather.

The models show an extremely moist and unstable air mass remaining over the Philadelphia area for much of Saturday before a weak ‘cold’ front moves through later in the afternoon.

Considerable low level moisture will produce low clouds Saturday morning.   Any breaks of sunshine around noontime may result in widely scattered showers and thunderstorms.  More organized shower and thunderstorm activity is likely between 4 and 7 PM on Saturday as the weak front moves through.   Highest chances north and west. There are model differences regarding the amount of cloudiness/sun and also  temperatures.

Saturday—

  • Mostly cloudy in the morning some sprinkles possible,  a mix of sun and clouds in the afternoon. Low confidence on the cloud cover 
  • Widely scattered showers/thunderstorms during the afternoon, especially 3-6 PM.
  • High temps 88.9º sd 2.2º.  Very humid, dew points above 70º
  • Winds SW–> W  10-15 mph with gusts to 25 in the afternoon.

Sunday—

  • Mostly sunny
  • High temp 89.8º sd 3.0º  (high spread, uncertainty)
  • Dew points ~ 65º
  • Winds WSW 5-10 mph gusts to 15

 

Weather… and Other Things 'Up in the Air'