The actual weather in Philadephia and most of the adjacent counties was far different than had been forecast by a multitude of models including the Canadian and German models.
Incredibly, the GFS (where convective activity is not its forte) did the best with timing and precipitation placement. Something to consider going forward.
Philadelphia, Delaware and Chester counties have not (yet) seen any severe weather. In my neck of the woods, we haven’t had much of anything except for some rain earlier.
Satellite water vapor imagery suggests something might be developing just to our west that may move within the next two hours.
Last night’s 7 PM update mentioned that the GFS was downplaying the severity threat. But, with all the high resolution models showing severe weather, I would never have just gone with the GFS for today’s forecast.
Here’s the current radar which shows the heavier action going to our north and south.
There’s still some time for the other models to redeem themselves.
Updated on Thu 3:31 PM: This morning’s GFS model with its earlier precip arrival and its less impressive, less severe weather may be on-target. The lack of sunshine this afternoon has kept a lid on some of the instability. I guess we’ll see.
Tonight’s 00z NBM rain/thunderstorm meteogram for Blue Bell—
Tomorrow’s thunderstorm strength potential will likely fall into the severe category. Some “severe weather” parameters are forecast to be the highest I’ve seen so far this summer season. One parameter, “helicity” related to potential tornadic activity, is forecast to be substantially elevated at various times during the day. Another parameter, “shear velocity”, is also highly elevated.
Some of the other parameters that that have been elevated in previous storms this season (CAPE, Lifted Index) are not as high as they’ve been previous thunderstorm days, so we’ll have to see how it all plays out.
The latest HRRR suggests we might get some thunderstorms in the early morning (7 AM) , hinted at by the NBM. The heaviest activity is likely between 4 PM-11 PM, but other activity is possible around noon or 1 PM.
The general timing of all of Thursday’s storms is still best depicted by the NBM model meteogram posted below.
Updated- Added 16z NBM meteogram
First, most of this morning’s (Wednesday’s) models have backed off on the thunderstorm potential for Wednesday afternoon and evening. Some models maintain a slight chance from just south of the city into Delaware and south Jersey.
Thursday looks to be much more active, as a strong cold front approaches and upper air disturbances move through in advance of the cold front.
A warm front moves through early Thursday morning. Several models forecast showers and thunderstorms early Thursday morning with this warm front.
Additional showers develop early afternoon and then again in the late afternoon and evening. Some of the dynamics may be very strong late Thursday afternoon, as the forecast jet stream energy has increased from previous model runs.
The actual front moves through around midnight and before dawn Friday.
I’ll be updating later this afternoon and evening with more specific information. Stay tuned.