UPDATE 3/1/12: I now have the data from the entire outbreak. The map below is a combination of rotation tracks, hail tracks and the confirmed storm survey start points, which helps us estimate a storm's progress much better. I believe we can blame yesterday's tornadoes mostly on three supercell thunderstorm tracks, the longest being 550 miles, although it appears to have split off into a second 450-mile track, sprinkling tornadoes over a 1000 miles.
Henry also pointed out, and this is very interesting, it would appear (unless the radar data is fooling us) that each time the hail from the storm decreased, a tornado was spawned, then the hail increased again. However, the storms to the south showed similar hail variance, yet spawned no tornadoes (surveyed so far). This is not a forecasting technique recognized officially but it warrants further research.
Thanks Henry for the tip. Looking at the radar loop from the tornadoes last night, it looks like the same area of energy (mostly the same supercell thunderstorm)* traversed over 800 miles from northeast of Tulsa, Okla., yesterday evening into West Virginia this afternoon. It was the same storm that caused the heavy damage in Branson, Mo., as the EF-2 damage in Elizabethtown, Ky., and also hit Metropolis, Ky.
However, it appears to me at this time (just looking at radar loops (see below), pursuant to receiving archived rotation signature data from WDSII) that it was a separate storm cell that caused EF-4 damage in Harrisburg, Ill. A tornado was striking both Metropolis and Harrisburg at the same time, in different parts of the line of storms (see radar below).
*It is worth noting that, although it appeared to be the same energy, or the same location in the line that traversed the 800 miles, the supercell's intense core did dissipate and regenerate several times. It's arguably not as good of a consistent track of a single storm as that from the Alabama tornado last April. Here is a radar loop between Branson, Mo., and Kentucky between last night and this afternoon. You can also download it or download an alternate which is smoother but not as long chronologically or as high resolution.
How can I confirm this storm track? I obtained those rotational signatures for 1-3 p.m. today but when I get access to more I'll present the entire chain, which will confirm my assumptions above. This is what the two-hour image looks like (it's rather brilliant, they just overplot the rotational velocity couplets for each radar scan).
The historic Mideast snowstorm and upcoming U.K. Christmas storm observed through computer forecast model images.
A pair of mesoscale vortexes formed over Lake Superior yesterday. I pulled up 3-D radar data just before the storms made "landfall."
A major snowstorm is headed to the Northeast U.S. -- including AccuWeather HQ.
The lake-effect snow machine is cranking out some incredible amounts during the first 24 hours of this major outbreak. Here are top amounts, webcams and 3D radars:
The coldest air of the season plagued Montana and surrounding Canada last night, knocking temperatures well into the -40s F, with wind chills in the -60s!
We're on day two of a major winter storm stretching from Mexico to Canada, about 2,500 miles according to radar data.