The Iceman

Mesoscale discussion out Mesoscale Discussion 2052 NWS Storm Prediction Center Norman OK Aug 20, 2026 17:53Z Areas affected...parts of southeastern Pennsylvania...central and southern New Jersey...north central and eastern Virginia...much of Delaware and Maryland. Concerning...Severe potential...Watch likely Valid 201753Z - 202000Z Probability of Watch Issuance...80 percent SUMMARY...Thunderstorms are likely to develop and intensify through 4-6 PM EDT, accompanied by the risk for a couple of tornadoes initially and increasing potential for strong to severe gusts spreading toward coastal areas into early evening. DISCUSSION...Moderate to strong boundary-layer destabilization is ongoing across much of the northern Mid Atlantic, particularly within seasonably high moisture content air advecting northward through the coastal plain, to the east of deepening (albeit weak) surface troughing to the lee of the Blue Ridge. This is occurring downstream of mid-level troughing, with at least a couple of convectively generated perturbations and belt of augmented westerly flow (30-50 kt in the 700-500 mb layer). It appears that associated forcing for ascent may increasingly begin to impact a corridor from central Maryland through southeastern Pennsylvania by 20-22Z, if not a bit earlier, supporting the initiation of intensifying thunderstorm development. At least initially, this may include a few evolving supercell structures in the presence of strong deep-layer shear. Downstream of a developing wave along a weak low-level baroclinic zone strengthened by differential heating, low-level hodographs are forecast to remain modest to weak. However, they may still be sufficient to contribute to potential for a couple of tornadoes, aided by appreciable near-surface buoyancy developing in associated with insolation, warm advection and dew point increases into the lower 70s F. Otherwise, at least some upscale growth of initial storms will contribute to increasing potential for damaging surface gusts, with additional thunderstorm development southward along and east of the deeper lee surface troughing. ..Kerr/Smith.. 08/20/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...PHI...AKQ...CTP...LWX... MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

5% TOR for extreme SE PA/S NJ/DE. Meso models this morning really liking this area for both strong storms and flash flooding. 06z 3K NAM and 12z HRRR are both nasty later on. NAM with a supercell threat while the HRRR is showing a huge QLCS for this evening. https://www.tropicaltidbits.com/analysis/models/nam3km/2026082006/nam3km_mslp_pcpn_frzn_neus_14.png https://www.tropicaltidbits.com/analysis/models/hrrr/2026082012/hrrr_ref_frzn_neus_12.png

Have gotten 0.0" this week. Back to drought it looks like. Can't ever remember a summer like this where we flip back and forth from weeks of dry broken up by flooding rains then back to weeks of dry.

Up to 4.65” after the lunch time heavy shower. Extra soupy out there

Round 3 beginning now, we might get over 5 inches total…

4.2” overnight and this morning. Much needed! Seems like we only do flooding rains or drought this summer, no in between.

Sigh one of these days we’ll have an event that isn’t a complete snoozer. Not gonna be today though

Yeah we had that brief downpour around noon and then nada. Honestly doesn’t feel as humid as earlier either. I doubt that line makes it through se pa intense but hopefully it holds enough for a period of steady rain. Was surprised to see the tornado watch for our area tbh

I thought we’d see more development out ahead of the front but it’s all been pushed NE. I’ll be surprised if the stuff out west holds together, doesn’t even feel humid out here with the wind.

Already a quick .40” from a cell that popped right over me. Radar lighting up to the west, I think we see multiple areas of flash flooding this afternoon.

The 12z 3k nam for tomorrow would be a flash flood disaster. 3-6+”(I saw lollipops of 10”) plus of rain right along the I-95 corridor.

Hyped severe weather underdelivers like 99% of the time in this area. Our best severe events are always like a random marginal or slight risk that over performs.

Not even close near me. .1” tops. Lasted 5 mins

Lower bucks and montco have gotten literally nothing… be thankful for .5”…

My guess is the Berks cell and and the supe to the SW are causing interference… as is though you and I are going to split the upright

Stuff in SE PA having a tough time getting going.

The cell in NW Jersey has a nice couplet on it right now. Another cell popping in burl co going into a good environment, debating crossing the river and intercepting

The NJ Governor just closed the state at 2 PM, I guess this is going to be bad

Meh heavy rain but that’s it. I will say the thunder got me out of my desk to check was going on though lol looks like LV is initiating now, probably kills their severe threat and might kill ours too to the south

That cell in central bucks quickly went supercellular. I’d expect a severe thunderstorm warning on it soon

Great write up Newman, was hoping to hear your thoughts I’m really liking my backyard we are in a great spot for instability and shear.

Lots of lightning outside of the storms, just had a really close strike by my house and we are a good 20-25 miles from the rain

Yes, that was also a very messy convective day in the morning but it didn’t matter because the deep layer shear was in place. Very similar set up.

Sounds like a tornado watch is incoming… pretty strong wordage in the Mesoscale discussion: DISCUSSION...Strong boundary-layer heating of a very moist air mass is ongoing across the discussion area as of 1645z, contributing to moderate/pockets of strong surface-based instability. Thunderstorms will continue to increase in coverage across the higher terrain, and along a north-south confluence zone across southern PA south into northern VA, during the next few hours. As coverage continues to increase and low-level lapse rates steepen, the potential for damaging gusts will increase across the discussion area this afternoon and early evening. Additionally, low-level shear will remain locally enhanced in the vicinity of a warm front across southeast PA/southern NJ. Deep-layer shear will be supportive of supercell structures, and the risk for tornadoes, potentially strong, will be maximized in this area.

With that main system going northeast of the city this morning, there should be a boundary set up right across SE PA and SNJ. Actually looking like one of the better non tropical tornado threats in a while. There’s going to ample instability in place for areas that miss the rain this morning which was my main concern going in. I’m debating going out to chase later if it develops how I think.