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Sunday Update

Posted Sunday 07/19/26 @ 9:55 AM — The clouds have lifted, but it’s still hazy out there. The latest smoke model shows a near-ground reading of 10 at 11 AM, much lower than yesterday’s reading near 100—

The near ground level reading goes to near zero Monday morning, but the sky may still not look fair-weather blue, because there will still be smoke at higher levels of the atmosphere.

Sun 10:03 AM —Yet Another Forecast Review — I have to share that I’m disappointed with the model forecasts from yesterday. In our area, multiple forecast models failed to accurately capture yesterday’s weather.

I’m very glad there was no really severe weather as had been forecast and that the Phillies game wasn’t overly affected. However, there were too many models suggesting very severe weather when it didn’t happen for the most part in the immediate PHL area. Indeed, the Philadelphia area, which several models had as the bullseye for extremely heavy rain a day prior turned out to receive very little. The final MRMS captures the total rainfall—

So the question is, are the models suffering from a lack of real upper air data?

Commentary

With the budgetary reductions taken by the current administration, the number of weather balloon (radiosonde) launches has become erratic and reduced.

Weather balloons with instruments that capture such things as temperature humidity and pressure are launched twice a day, at 00z (8 PM EDT) and 12z (8 AM EDT) world wide. These measurements are essential to establish what’s called initial conditions for accurate modeling of the atmosphere.

Here’s a typical number of launches (still reduced from previous years) this past Friday evening—

Here’s what was launched on Saturday morning—

I think the images speak for themselves.

Missing so much data upstream from us seriously affects the accuracy of weather model forecasts. This is unacceptable!!

Sat 7:38 PM —Forecast Review — Many areas in the immediate Philadelphia area have seen little in the way of heavy rain and severe storms. Most of the activity was in Bucks county, Central and Northern NJ and NY. The current rainfall shown in the latest MRMS shows this—

The RRFS, HRDPS and HRRR all show varying degrees of divergence/storm suppression over the immediate Philadelphia area this evening into midnight. We’ll see if this comes to pass. Always listen to the NWS for official warnings.

Saturday Forecast Update

Posted Saturday 07/18/26 @ 12:58 PM — For the record, I’ve resurrected my “parameter severity table” that compares today’s storms with past storms. For consistency, I’m using today’s HRRR, although I’d like to transition to the RRFS in the future.

You can see that today’s storms are highly comparable to past severe weather outbreaks. ( FYI, These high numbers were mostly found in South Jersey southern Salem and Cape May counties.)

Saturday Forecast Updates

Posted Saturday 07/18/26 @ 11:22 AM — The storms that eventually developed just to our north were produced by a warm front that is moving towards NYC at this time Last night’s model’s haven’t been too helpful. Here’s the current radar—

New 12z models with updated upper air data from weather balloon launches may provide some better guidance for this afternoon. The latest 12z RRFS, while still not handling the current radar, does appear to offer some insights.

It has some sun breaking out around 1 PM-4 PM. This will heat up the already unstable atmosphere.

A line of strong storms develops to our west and moves northeastward about 4-5 PM. These will mostly affect northern Montco and Bucks counties. Some may be severe.

By 6-7 PM, additional storms, some likely severe, move through—

By 10 PM, the cold front approaches with more storms—

The above graphics are provided as a rough guide. No model accurately predicts the exact location and timing of severe thunderstorms.

Posted Saturday 07/18/26 @ 8:27 AM — None of last night’s models really come very close to matching the current radar—

Nonetheless, the area of storms just to our west will move into parts of Philadelphia in the next hour or so. This was partly predicted by last night’s Canadian models, but the HRRR, RRFS and NAM-NEST didn’t show any of this. Trying to nail down the timing of the storms this morning doesn’t look possible at this time as the 06z model runs still aren’t capturing reality.

That said, the period of the most severe weather remains 3 PM through 8 PM and later in S Jersey and Delaware. The models also hint at another line of showers moving through between 10 PM and midnight.

Here’s the current Model Blend that gives an idea of the difficulty in nailing down the timing—

New models based on 12z upper air measurements will be trickling in over the next few hours. I hope to update before noontime with more details on severe weather.

Severe Weather Possible Saturday Afternoon

Originally Posted Fri 8:43 PM — A series of disturbances with plenty of energy will converge on our general area on Saturday. Since this is being driven by two separate pieces of energy, there is some disagreement among the models whether the more severe weather will occur in NY State or nearer Philadelphia.

The current water vapor image shows the two disturbances—

I’m not sure how well the new RRFS is handling of this complex system, but its forecast is somewhat similar to the HRRR. It is favoring a more northern severe weather forecast and it has very little activity around here Saturday morning.

The ECMWF as well as the Canadian GDPS with “AI Spectral Nudging” and the GFS show thunderstorms moving through Philadelphia around 8-10 AM, followed by a break in the action. We likely will see some breaks of sunshine through high clouds and residual smoke late morning into early afternoon.

The real action occurs between the hours of 3 and 8 PM. With sunshine earlier, very high instability, high PWAT, severe storms are likely to form in several lines moving from northwest to southeast. The Model Blend shows moderate probability (for this region) of tornadic activity around 3-8 PM.

Additional line of storms move through around midnight!

The RRFS SWEAT index shows a few areas exceeding 400, the threshold for severe weather like tornadoes at 8 PM —

Those areas of severe weather expand as they move eastward into NJ by 9-10 PM.

Rainfall amounts may range 1.5-2″. Some localized, heavier accumulations likely.

The Canadian HRDPS seems to capture Saturday best—

I expect that by Saturday morning, things will better clarify regarding timing.

Saturday

A stormy day, with thunderstorms possibly beginning as early as 8 AM. Severe thunderstorms and possible tornadoes are looking likely during the late afternoon and/or early evening. There may be some breaks of sun late morning or early afternoon. Very humid and becoming windy. Lines of strong storms will move through from 3 PM to 9 PM. High temperatures 85º Blue Bell, 88º Philadelphia. High uncertainty with a sd of ± 4.1º

Sunday

Becoming mostly sunny Highs (Model Blend): Blue Bell- 81 º Philadelphia 83º ±4.0º High sd and uncertainty.