Updated Wed 3:32 PM with precip map

A quick post here….As described in my previous post, a front will move through and stall just south of the Philadelphia area.

Some scattered pop-activity possible late this afternoon.

The main frontal activity will move in this evening (Wednesday evening). Latest models have storms affecting immediate PHL area from about 8 PM through midnight, starting in far northwestern suburbs earlier. Severe activity possible far northwestern suburbs; heavy activity here.

Not all models are on-board with the above GFS forecast of excessive rain.

Main event appears to be Thursday mid-afternoon (2-3 PM) into night with additional heavy rain/storms.

Stay tuned for updates.

Forecast Updated 7:06 PM– Looking further at the latest GFS, some thunderstorms may fire up again at 11 PM to midnight.

Forecast Updated 6:15 PM– The latest GFS, just available, shows considerable convective inhibition (see update below) as the storms approach Philadelphia. As mentioned earlier, this may cause the storms to weaken as they approach. The exact point of weakening may be to our west, or just to our east, as the GFS is a relatively low resolution model. Much of the energy is being held back, as the main front will pass through on Tuesday with additional rain. We will see.

Forecast Updated 12:10 PM in highlighted text below:

A strong cold front will approach this evening. Ahead of the actual front, a prefrontal trough will trigger thunderstorms in the Philadelphia area this evening, likely starting between 5:30 6 PM and and 8 PM. Additional thunderstorms may move through up to around midnight.

Conditions are favorable for moderate to strong severe thunderstorms with CAPE values (convective available potential energy) in the 1500 J/Kg range and instability values (Lifted Index) around -5..5ºK. (More negative is stronger here.)

The latest HIRESW-ARW and HREF show higher CAPE values, in the 2000 + J/Kg range, especially western suburbs. Expect moderate to severe thunderstorms as early as 5:30 PM in far western suburbs, with heavy rain, moving into Philadelphia. They may weaken as they move further east.

All models show high CIN parameter inhibiting thunderstorm strength, just east of Philadelphia into NJ developing by 9 PM. So any thunderstorms making it into NJ may weaken.

Precipitable water values are high, in the 1.7-2” water range.

Last night’s models show considerable diminishment of the activity as it enters into NJ after 8 PM, as shear and storm motion vectors become opposed. CIN (“Convective Inhibition”) values become elevated in NJ after 8 PM. (Think of CIN as the anti-energy of CAPE.) Of course, this could change.

Last Monday, the GFS did the best with timing in a somewhat similar setup and I’ll be leaning on this for today.

I’ll likely update sometime during the afternoon.