8/19/2005: FCST: Upper OH Valley/Eastern Great Lakes

Looking at 00Z model runs early this morning, I think the tornado outbreak-making system from yesterday may work its magic again this afternoon. By 00Z, NAM paints 3000 j/kg or so MLCAPE over western PA, combined with sfc temps in the low 80s and dewpoints near 70....LCL heights will be decently low. Another thing is the absolutely beautiful wind structure, vertically, along the warm front. Sfc winds will be outta the SE at 10-20 kts, SSW 850-mb winds of 40 kts, and WNW 700-mb winds near 45 kts. This will lead to very strong shear profiles, and NAM shows that with 0-3 km SRH over 500 m2/s2 over the western half of PA by 00Z. If this holds true, any supercell that gets going near the warm front may drop a strong, long-tracked tornado.

I know Pennsylvania isn't the best chase territory in the world, by any means, but it may get really active there later today.
Lets not forget Southern Ontario. We've already had a couple nice storms rumble through today. With more expected throughout the rest of the day.
After analyzing some data, I'm beginning to wonder if eastern OH/western PA/western New York State/southern Ontario is going to see a repeat of May 31, 1985 this afternoon. This is what happened that day: 41 tornadoes touched down in Ohio, Pennsylvania, New York and Ontario, Canada. At least 76 died in the United States, and an additional 12 perished in Canada. The damage reached over $450 million. I hope we don't see a similar outbreak today, but after what it this system did in Wisconsin, I wouldn't be suprised by anything. The area outlined in Moderate Risk today is the exact same area that was devasted twenty years ago. I especially hope we don't see anything like the Niles, OH/Wheatland, PA tornado, which reached F5 intensity and completley leveled the town of Wheatland, as well as the F4 tornado which cut a 65 mile long, nearly two mile wide path of destruction through the Moshannon National Forest and the town of Lock Haven. But, seeing as it produced what looks to have been an F4 that smashed through Stoughton, Wisconsin yesterday, I don't see why it can't produce another violent tornado today. The setup is very conducive to them. My prediction: we will see at least a dozen tornadoes today across this area, maybe more, one or two of them possibly strong to violent.
May 31, 1985 was an incredible outbreak, for sure. However, to say this will be one like that one is kind of like predicting a particular day in the southern plains will be another May 3, 1999. While it might just be (let's hope not), odds are that it won't. Regardless, conditions are indeed becoming favorable for at least a few tornadoes in W PA.

Big problem right now appears to be cloud cover. All of PA is virtually socked in with both low-level and upper-level cloud decks. There is a bit of drier air at the mid-levels (per water vapor imagery), but I don't really think there will be enough of a dry slot to get sufficient insolation for strong instability to develop. The 12z ETA has latched on to this, and only develops CAPE up to 2000 j/kg in W. PA.

There is nothing wrong with the wind profiles there, with good speed and directional shear. SRH is forecasted to be more than sufficient for tornadic supercells, given some instability.

I believe there will be some tornadoes today, but I don't believe we will see anything like what we saw yesterday in WI. I believe the key to yesterday's outbreak was the presence of very dry air at the mid-levels which allowed insolation to occur and limited the number and coverage of storms. Setups like yesterday occur reasonably often in the Upper Midwest, but storms usually undergo a quick transition to a linear convective mode which effectively ends the tornado potential (except for embedded supercells).

Latest mesoanalysis indicates that some of the parameters are displaced somewhat and I am beginning to be a little skeptical that this event will be as major as the event in WI on yesterday. The best instability remains a little further south of the area into KY. CLE hodographs indicate rather sufficient shear from the 0-6km level as the inversion is beginning to weaken which is still about 600 meters between the LFC/LCL. Things should get going as a s/w exits Indiana and plays role as yet another lifting mechanism in the region. The moisture column above 850 mb is not all that impressive either.

Yes, I've been following this setup intermitently today as it is close enough to my location to at least hold some interest. Forecast directional shear profiles finally seem to be coming together, and a clear slot has emerged over the afternoon over OH. W/ moderate CIN in place, would like to see SB CAPE building at a more pronounced clip, but starting to get skeptical. Effective deep layer shear of 60 kts +, surface low deepening as advertised - and I especially like the SR winds at all levels. W/ strongest instability pooling further to the S & W of best upper-level dynamics, however, far from sure it will all come together. Gabe mentioned the LFC / LCL differentials, which have been all over the board w/ each mesonalysis update, and I would add that the topography in this area seems to play havoc w/ the practical application of these measures to convection. Remnant stationary front / wind shift line over N WVA & VA abetting some backing of surface winds, but surface moisture convergence difficult to pinpoint.

One of those intriguing, somewhat rare, eastern severe setups, but it's got to come together just right, and I'm not sure the juice will be there for late afternoon isolated supercell initiation over PA. Now, system is still strong enough such that I wouldn't be surprised if we see an evening MCS further north, coming off the lakes, and into NY vicinity.