WEEKEND WEATHER OUTLOOK – THURS

The slow-moving front that moved through Wednesday with thunderstorms will become a stalled, diffuse frontal boundary to our south; it will serve as a track for weak disturbances (areas of vorticity)  to move near our area from west to east over the weekend.

The summer daytime heating combined with these areas of vorticity and moderately high moisture (precipitable water values  about 1.5 inches) will result in instability and mostly afternoon and evening thundershowers, some which may be slow moving causing considerable downpours.  Many areas will also see a fair amount of sun, especially east of the Philadelphia into NJ.  Highs both days near 90.

Currently,  the models show areas to the west of Philadelphia to be the most impacted by this setup on Saturday.

The current GFS shows showers to our west Saturday afternoon, but significant sunshine in other areas. (see graphic)

GFS Forecast Precipitation Rate and Cloud cover for 1 PM Saturday (green lavender =rain)

Sunday shows more clouds but fewer areas of showers—

GFS Precipitation Rate and Cloud forecast Sunday 4PM

This sort of scenario is impossible to nail down to specifics, despite the pretty graphics; it’s presented to provide an approximation of what to expect.

What will be interesting to see is whether some showers break out around 3-4 PM today (Thursday) in Philadelphia.  My view of weather models- if the short range forecast shows to be inaccurate, the longer range forecast should be taken with a grain of salt.

WEATHER UPDATE

There are interesting differences in last night’s models regarding the chance of showers/thundershowers this evening. (Sunday evening)

An upper air disturbance drops down into our area this evening, between 7PM and 1 AM.  The NAM has been consistent in keeping any showers far to our north.  One version of the WRF with NAM physics (WRF-NMMB) also does the same.

The GFS  (and its similar physics version, the WRF-ARW) has showers and thundershowers making it in to the Philadelphia area towards midnight, then dissipating.   It will be interesting to see which model does the best here.

Either way, today will be hot and slightly more humid. Highs 91-93 with dew points near 60.

WEEKEND WEATHER FORECAST

There isn’t much change from yesterday’s posted outlook.

Sunny skies and warm Saturday. High 88-90.

Tonight’s NAM suggests that a weak warm front moves through late Saturday afternoon.  Some cloudiness possible as a result with an increase in dew points Saturday night.

Sunday is sunny, hotter and more humid. High 90-92.

There’s a low chance of a very widely scattered brief thundershower on Saturday , late afternoon. Most areas dry.

Tonight’s WRF has a greater chance of thunderstorms Sunday evening.

Weather… and Other Things 'Up in the Air'