Category Archives: Weather Forecasts


A front slowly moving through Thursday will cause heavy rain to fall in the Philadelphia area.  The latest NBM cranks out several inches of rain for our area, about 2.5 -4+ inches, with even some higher localized amounts!  The heaviest rain north of the city.

Model Blend 5 PM accumulated Rain—

NBM accumulated rain 5 PM Thursday  (Click on image for a larger view.)

I’m going to be without weather model access for a few days, so there won’t be the usual sort of updates for this weather event tomorrow, nor will there be my regular weekend weather forecast.


It’s been a long time since we had an uneventful three day forecast, and it seems even longer that this occurred on a major holiday weekend.

The  general pattern is one of high pressure building in from Canada, bringing clear skies and comfortable temperatures with low humidity.

The model blend (NBM) should be more than adequate for this forecast —

Sunny skies Saturday, Sunday and Monday.  Highs 78°, 83° and 84°



Fri 11:00 PM Update — Tonight’s models suggest the rain will be more showery in nature on Saturday— Breaks in the rain interrupted by some heavy rain periods. Winds look a bit more gusty as well. Some clearing late afternoon will be interrupted by scattered thunderstorms late afternoon and during the evening. Some areas will receive much more rain than others. Not a uniform continuous rain event. The HIRESW shows some of that extreme tropical moisture makes it into Philadephia, so localized heavy rain possible. The forecast below remains mostly intact.
The moisture and energy remnants of Hurricane Laura will move into our area on Saturday.  The low pressure system that was Laura will merge with a large non-tropical low pressure system and associated cold front on Saturday into Saturday night.

The moisture maximum, as reflected in the precipitable water parameter, or “PWAT” maximum,  will move just to our south, as previously forecast —

GFS PWAT forecast for 2 PM Saturday afternoon (Click on image for a larger view.)

The energy associated with both Laura, the non-tropical low, and the cold front will move through in separate batches.  Showers and rain will move through during the overnight hours.  There may be a break in the action Saturday morning, but rain returns around noon and continues though the mid afternoon.  Total rain about 1 inch, locally higher.

GFS (pre-release version) 6 hour rain accumulation at 2 PM Saturday. (Click on image for a larger view.)

The GFS (new pre-release version) has rain ending around 5PM with even some sun possible later Saturday afternoon.  The HIRESW has similar forecast, but has additional showers and clouds after 8 PM with the actual cold front passage.


  • Rain and cloud details above
  • High Temp 81º sd 2.1º  Dew Point 73-74º
  • Winds SW 5-10 mph   Gusty mid afternoon.  Becoming NW around 10 PM after the cold front passage

High pressure builds in for Sunday. A few upper air disturbances may produce periods of “fair weather clouds” and instability stratocumulus.


  • Sunny early, then  a mix of sun and clouds in the afternoon.
  • High temp 78.6º sd 1.3º
  • Low Humidity. Dew points upper 50s.
  • Winds WNW  10 mph becoming gusty to 20mph in the afternoon.


Sat 07:43 PM Update — Today’s HIRESW along with other models do support more shower activity on Sunday. Showers and thundershowers are possible anytime between 11 AM and 5PM Sunday. It appears that many areas around PHL will see some shower activity.
Sat 09:18 AM Update — Later runs of the NAM-NEST and two pre-release versions of the HIRESW do not support the heavy showers predicted by the HIRESW-ARW last night, as mentioned in my previous ‘update’.  The latest model blend (NBM) still includes the Sunday showers.

So there’s uncertainty in the forecast for Sunday.   I’ll keep an eye on this.

Fri 11:20 PM Update — Tonight’s HIRESW-ARW models show significant showers and thunderstorms on Sunday. This is a significant change in the forecast. I’ll update again over the weekend.

A Bermuda high pressure system off the southeast coast will bring increasingly warm and humid weather to our area. Weak disturbances moving around the periphery of the high pressure system will bring occasional clouds and slight chances of widely scattered showers and thundershowers.  Most of our area this weekend will be dry.


  • Cloudy early morning with a slight chance of a light shower. Clouds break for partly sunny/partly cloudy skies by late morning or early afternoon.
  • High temp 86.2º sd 1.3º. Dew points 66º-70º
  • Calm to very light winds from the SW 3-5 mph
  • Slight chance of a widely scattered shower late afternoon. Most areas are dry.

Sunday —

  • Some fog and clouds early.
  • Sunshine breaks through after 10 AM
  • High temp 87.8º as 2.3º.   More humid. Dew points 68º- 70º
  • Calm winds in the morning.  Light winds up to 10mph in the afternoon.
  • Chance of thundershowers late afternoon, far northwest areas. Philadelphia is expected to be dry.