Category Archives: Thunderstorm Outlook


Forecast Review — Last night’s models, which had been more conservative with the forecast severe parameters, were more on target with their thunderstorm forecast than this morning’s models.  We had several hours of clouds this afternoon which reduced the available energy when the storms arrived. It’s not the first time I’ve seen the 24 hour forecast be more accurate than the “latest models”.  
With thunderstorms, sometimes you’ve got wait for the latest models.

This morning’s models just becoming available have a significant increase in the severity parameters- helicity, CAPE and vertical shear.  Precipitable water values (PWAT) are very high.

So my previous post is off the mark.

Expect thunderstorms, 5-8 PM in the immediate Philadelphia area.   Some could be severe.

HRRR Helicity forecast for 7 PM Thursday. Anything over 300 J/Kg is high. (Click on image for a larger view.)


Thu 07:12 AM Update —  Regarding the thunderstorms being forecast for Thursday evening, the storms are forecast to move through about 5-7 PM.  The severity parameters in the immediate PHL area are at low to moderate levels.  The latest models have most of the stronger activity closer to and south of the PA-Delaware border.  Localized heavy rain still possible.  I’ll keep an eye on this.
  • CMC HRDPS 6 PM 1 hour Precip


From Wednesday evening…

The models have been on-board with moderate to heavy thunderstorms moving through our area about 10-11PM tonight.

Severe parameters are in the moderate range, but precipitable water values (PWAT) are very high, so some heavy downpours are expected this evening.  The storms are fast moving— expect some very gusty winds with these storms, as they quickly move through.

A front moves through Thursday early evening between 5 and 8 PM.  I’ll be updating tomorrow morning on those storms.

Addendum 9:07 PM:  Tonight’s storms are expected to diminish in intensity as they move into NJ.  Model blend thunderstorm probability at 10 PM—

NBM 1 hour Thunderstorm Probability 10 PM



1:00 PM Update- Storms approach  3-4 PM according to the latest HRRR

A quick post- models are on-board with thunderstorms today in the immediate PHL area, from 3-6 PM, moving northwest to southeast.   Several models show closer to 4 PM.  Severe storm parameters are in the moderate range.   Some quick heavy rain possible, gusty winds.

More storms after midnight.


Thu 02:53 PM Update — Thunderstorms look much less likely this afternoon and tonight. It also appears that we won’t hit the highly advertised 94º high temp today.

My previous post postulated that it’s tougher to accurately forecast the weather with a tropical system in the picture.  That’s not going to stop me from trying.

Tonight’s models are just becoming available. A warm front moves through overnight and dew points rise almost 10° by 8 AM.

Tonight’s models show some scattered/isolated thunderstorms developing between 5 AM and 7AM Thursday morning with the warm frontal passage.  The ‘severe weather parameters’ are fairly elevated at that time, so while these storms will be isolated, they may pack a punch.

Some models are showing more thunderstorm activity late Thursday afternoon and evening.

Unfortunately, I’m unable to access the HIRESW model this evening.