Wednesday, February 06, 2008

Winter tornadoes

We've lived quite a few places in our lives where people talk about tornadoes. One of the things I discovered shortly after moving to Tennessee, though, was that here they don't just talk about tornadoes, they actually have them. Sure, places like South Carolina, Georgia, Florida, and the Colorado Front Range do sometimes get real tornadoes, occasionally real whoppers. But for the most part they are a peril far more feared than actually encountered. Much to my surprise, that is not the case here. I had hardly been on this land a month before I saw a small (F0) tornado spawned by a hurricane remnant travel down our hill behind the house, cross the road, and suck up a cloud of spray from the neighbors pond. Within a year we experienced tennis-ball-sized hail from a storm that had killed nearly a dozen people before it reached us. Close Encounters of the Supercell Kind are not rare things. The only major US city to have received a direct strike on its downtown high-rise district? Nashville.

Last night a strong, long-lived supercell formed in northern Mississippi and tracked all the way across Tennessee into Kentucky, dragging a tornado most of the way. I didn't pay too much attention to it when it first developed, as it was far from us and most run-of-the-mill supercells don't live that long. But as the evening progressed, it travelled into southern Tennessee, heading in our general direction, and held its form quite well. Reports from the ground indicated that it was indeed producing a tornado while its dopper radar signature continued to show strong and large circulation. Every time I held a straight edge up to the computer screen to track the center of the circulation, it seemed to be pointed awfully close to our direction. Finally when the tornado warning reached us, and the radar still showed this circulation center tracking to within a mile or so of our house, we cleared out the closet under the stairs, gathered dogs and blankets, secured doors and windows, shut off computers, and got ready to take cover.

The lightning show was spectacular and largely without thunder, as often seems to be the case with these tstorms. Flashes were coming many per second, illuminating the low scudding clouds flying from the.. um... ok...east to west. This mean they were spiraling rapidly around and into the circulation (prevailing winds were southwesterly). Our surface winds were strong but not dramatically increasing, also coming from the east, meaning we were within the surface inflow circulation of the mesocyclone. We kept peeking out as the winds shifted around to be southerly and southwesterly again, and the lightning flashes finally shifted to our north. The cell and its possible tornado had skirted just barely to our northwest.

As the storm receded, I phoned my mother (who lives in town, outside of the track of this storm) and it became rapidly apparent that the tornado had been actual, not just possible. She had her police scanner on, and the calls began coming in almost immediately from just down the road from us: trees down, power lines down, buildings damaged. I brought the computer back up, looked at the doppler radar loop, and saw that the strong circulation center had tracked just a mile or two from us and continued along the northwest edge of the county. On the scanner, the emergency workers were naming roads whose locations matched up perfectly with this track.

First thing this morning I headed down the road to see what the situation was. Within a couple of miles I came to orange traffic barricades, which I drove around on the justification that I am a card-carrying trained storm spotter (plus there was not an actual "road closed" sign). I only saw a few downed trees at first, but then I came in sight of the storm track. It was quickly apparent that this had been a significant tornado. Here are some pictures (click any for a larger view):

Extensive tree damage, of course:

Our road is not normally a single track through a brushpile:

Foreground tree damage, background structure damage:

When they tell you trailers are not safe in severe weather, believe them. See how many of the dismembered parts of this mobile home you can identify:

Some of the missing pieces of that trailer can be found here:

Windblown debris and wreckage piled along tree and fence lines in a way that reminds me of the aftermath of a flood:

One of the classic signatures of a tornado: trees felled in intersecting, converging patterns. In contrast,straight line winds flatten trees in parallel or diverging patterns:

More explorations and plotting revealed that the tornado missed our house by less than a mile. So when we were peeking out the front door last night listening and watching, the funnel was literally just beyond the ridge, almost on top of us. And it wasn't even raining.

Farther down its track, the tornado lifted just long enough to avoid giving downtown Nashville its second direct hit. But then it redeveloped and intensified, killing 17 people in Tennessee and triggering a massive fire at a natural gas facility before crossing into Kentucky.


Post a Comment

<< Home

Site Meter