Thunderstorms WEDNESDAY

Updated Wed 8:40AM, highlighted below:

Updated Wed 8:25 PM: This afternoon’s GFS has heavy rain blossoming around Philadephia between 8-10 PM, while the HRRR and the RAP do not. Current radar seems to support the GFS. We’ll see soon enough.

Wednesday’s thunderstorm outlook is looking a bit like Tuesday’s, but with some differences. These storms will also be slow moving and will develop like today’s but will be moving southward instead of northeastward.

CAPE values only about 2000 instead of Tuesday’s 2800 J/Kg. Precipitable water still high at 1.9-2.0″ water, but also a bit lower than Tuesday. Instability values also lower.

Storms are possible in as early as 2-4 PM but eventually blossoming in the immediate Philadelphia area by 4 -7 PM and continuing into the late evening. There is some suggestion that areas south of the city and in NJ may be more affected, especially in the evening. Last nights’s models continue with a timeframe of 4-7 PM for the onset in the immediate PHL area, then continuing southward. Highest probability is 6 – 8 PM

Here’s their afternoon’s HREF precip forecast

High Resolution Ensemble 1 hour precip forecast for Wednesday. (Click on image for a larger view.)


Tue 04:57 PM Forecast Review — The models did well with the thunderstorm forecast for today. The storm activity should continue into the early evening. The latest HRRR is forecasting some intense dynamics around 6PM in Philadelphia and into NJ.

Some of lightning today was cloud->ground and was dangerously spectacular to view.   CAPE (Convective Available Potential Energy)  values today were high —in the 2800 range (compare to last week’s storms which were only in the 1700 J/kg range.)

A repeat performance expected on Wednesday, likely 2-6 PM and somewhat more in NJ.  

Another very warm day is in store for us on Tuesday. Temps will be in the upper 80s, but an increase in humidity will more than make up for it.

Upper air disturbances will move through, around noontime, triggering scattered showers and thunderstorms in many areas, starting as early as noon- 2 PM and lasting in some areas into the evening.

HREF (High Resolution Ensemble Forecast) hourly precipitation with standard deviation, at 12 PM, 2 PM and 5 PM with increasing areal coverage. (Click on image for a larger view.)

High CAPE (potential energy), high instability values and high precipitable water values could make for some heavy rains in localized areas. Overall, the models are cranking out 0.5 inches of rain.