beneficii

This to me is one of the crazier videos:

http://www.youtube.com/watch?v=nBbUhJnC70c&feature=fvwrel

Wow.

Actually I figured it out. Probably the low pressure inside the tornado that forced those off. Wind Speed alone can't do it since the surface is parallel. So manhole covers make a crude barometer.

And what would be the reading on that barometer?

We could probably take into account the mass m of the manhole cover, the area of its surface facing the outside A, the earth's gravity g, and the air pressure P0 underneath the manhole cover before it is lifted. That way we can find the difference in pressure from outside the sewer to inside the sewer DP, that is just below the absolute lowest possible, and the pressure outside P.

So, perhaps it would be something like this:

DP = m . g / A.

P < P0 - DP.

Yeah, the fact that some of the most violent and long-lived twisters hit highly populated areas really made heavy casualites inevitible, unfortunately.

Fatalities-wise, this may end up close to the Super Outbreak, but in terms of scope, not quite. 1974 had strong/violent tornados from the deep South all the way up to nearly Canada...13 different states, I believe.

Actually, there were a few touchdowns in Canada in the 1974 Super Outbreak.

Does anyone know the exact location of the front itself?

The surface frontogenesis product on the SPC Mesoscale Analysis page should give you a good idea. I think it's already crossed the MS River.

Oops. Forgot to mention the day... Was looking at Tuesday evening.

Thank you. It looked to me like West Tennessee might be spared given the timing and the lack of precipitation on Tuesday evening on the 12z GFS, but it may be that there is convective precipitation that is not picked up by the model.

Not that I need to repeat what some other great severe wx posters have already mentioned here, but the setup as shown by the GFS is as alarming as any I have seen on modeling in a long time. The LLJ is well out in front of the trailing cold front, and the upper level 500 mb jet punches squarely into the warm sector as opposed to staying near / parallel to the incoming cold front. The 250 mb jet structure is also ideal, as some areas are in both the right rear quad of the departing disturbance, and the left front quad of the stronger incoming one. Also, the GFS shows capping weakening by the evening over AR into western TN, which would spell trouble given storm mode could easily be supercellular / tornadic that far ahead of the front. Will be interesting to say the least to monitor future runs and see how this trends.

On what evening?