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Storms Thursday Evening
Updated Thursday 06/11/26 @ 4:40 PM —The models show the heaviest storms will be in the western suburbs of Philadelphia this evening. The storms may weaken considerably as they move into NJ.
Updated Thursday 06/11/26 @ 12:05 PM — The edge of a tropical airmass will be at our front door this evening and very strong dynamics with high precipitable water and very high CAPE will cause thunderstorms to form and be potentially quite severe. Here is the latest RRFS forecast derived “theta-e frontogenic forcing graphic indicating strong upward motion and energy.
The only ingredient missing is a uniform layer of high humidity at 700 mb (10,000 feet), suggesting possible less organization with the storm clusters. (See comments section for more)
Updated Wednesday 06/10/26 @ 10:05 AM —Warm/hot humid air is approaching our area and is rising over and replacing the relatively cooler air at the surface. (A warm air advection.) Much needed showers have developed as a result. The somewhat arbitrary line for a tropical airmass is the 760 thickness line (500-1000mb thickness) visible as orange in the GFS synoptic map below—
A weak cold front (more of a wind shift) will push through Thursday evening and night with the possibility of strong thunderstorms. Hot a humid weather is expected for Friday with additional activity over the weekend.
Updated Tuesday 06/08/26 @ 9:49 PM —A large pool of hot air is developing in the central US and the heat and humidity will attempt to move into our area on Wednesday in the form of a warm front. Significant rain is expected to develop during the day Wednesday along with thunderstorms.
There will not be much influence of a nearby jet streak, so rain and thunderstorms will develop unimpeded, although they may not pack the punch of having a jet level assist. As I’ve been saying for months, we need the rain!
You saw the heavy rain yesterday (Wednesday) a few days in advance. I kept checking the National Weather Service, and while they were acknowledging a reasonable (60%) chance of rain, they were not terribly excited about the breadth and scope of what was coming our way. As one data point, we received .77 inches of rain from yesterday’s storm in lower MontCo. The NWS was predicting .06 inches (with “higher amounts” possible in thunderstorms). I view .77 inches as a good amount of rain and certainly welcome given how dry it’s been.
So my question is, why do you think you were seeing the magnitude of yesterday’s storms when the NWS (the gold standard in forecasting) was more guarded in their analysis?
I’m not trying to ding the NWS–they are outstanding. But it feels like there’s something to be learned from their cautious approach to yesterday’s forecast given that you saw what actually materialized a couple of days in advance.
Also, are the storms today likely to be comparable to yesterday? I’d welcome another shot of meaningful rain.
Hi Brian,
Well, you won’t believe this, but over the past two weeks (and currently), I’ve been doing the blog forecasts remotely while in the Switzerland and French Alps. (I don’t like to broadcast when I’m away.) That said, I have had full access to my weather data via a VPN to my servers at home and I’ve been updating with graphics remotely via my iPad.
As I alluded to recently in some posts, with the help of Claude AI and ChatGPT, I’ve embarked on developing new (for me) somewhat advanced tools for forecasting weather. I’ve recently moved away from the usual standard model parameters (such as helicity, CAPE, vertical shear and the model forecast precip) and with AI help, my weather model downloads post-processing now calculate “derived parameters” such as “Q-Vectors at 500 and 700mb”, “frontogenic forcing” and something called “theta-e frontogenesis”, along with some others. While real meteorologists supposedly use these derived tools all the time, without AI, I could not have figured out how to calculate these derived values and display within the models.
Specific to the your question, I noticed the new RRFS was not that emphatic about the rainfall potential yesterday, BUT when I looked at the Q vectors and specially the frontogenic forcing that I’ve developed for the RRFS in anticipation of its release, the values were extreme. Combined with the ECMWF-AI model, significant precipitation looked likely.
I wish I were home to do the weather for tonight and I’m 6 hours ahead, (actually, the Swiss/French Alps are really nice). I’m traveling back to the US over the next 24 hours, so time to “do the weather” for tonight is limited. But I’ll take a fast look.