Tornado Corridor Impressions (pt2)

Seeing the tornado damage corridor (above) made me realize I'd actually heard the tornado from my deck.

I'd been watching the weather sweep through--- it was an impressive group of storms, and it had caught my attention to the point where I had a radar loop running on my PC, tracking the storm's progress (the public Nexrad feeds update every 6 minutes or so). We were already under a flood watch from the intense rains of this and the previous series of storms, and I saw that the National Weather Service radar had flagged one cell near my house with the "hail" symbol (a solid yellow box).

I wasn't worried about flooding; I live on a small hill at about 800' elevation (240m), with no streams or lakes above me. But radar showed the hail-producing cell would pass a bit to the west of my home. That might be worth seeing. I'd been caught in the edge of a supercell's hail last summer in Colorado ( http://www.youtube.com/watch?v=GFdxvIKSYrU ) and we'd seen hail on the tornado chase. But I haven't seen a lot of hail in NH.

Outside, it was raining in gusty bursts, but the rain was warm and not unpleasant, so I went onto my deck to see what I could see. There it was: the hail cell was a darker mass of clouds just above the treetops to my west. (Remember, I'm at 800'; up near the cloud bases.)

As the cell passed close by to my west, I heard continuous crashing, and I remember thinking that this was a very active cell with lots of continuous lightning. I'd seen lightning like that on my tornado chase last Spring, so I knew that violent cells could produce nearly continuous flashes. This particular storm was in daylight, so the lightning wasn't well-visible, but the nearly continuous cracks and crashes easily were. The sound was very sharp, with lots more high-frequency snaps and crashes, not just thunder's classic deep cracks and rumbles. I attributed the sharpness of the sounds to the lightning being close by.

The active, dark mass of clouds headed left to right as I watched, moving north. The sharper sounds diminished quickly, but the deeper thunder faded more slowly. I went back inside, and a few minutes later, the radar tagged that same cell with the purple triangle symbol of "tornadic vortex signature." By then, the cell was north of my position.

After seeing the above photo, I realized that I'd been hearing not a continuous crash of thunder, but the sharper sound of tens of thousands of trees being snapped off, chewed up, and tossed around: the sound of a long strip of living forest being ground up by a tornado.

It wasn't at all like the "freight train" sound that people sometimes report when they hear a tornado.

An EF2 tornado has winds about 111–135 mph (179–218 kph). That's about the same speed as a free-falling skydiver. If you've ever had the pleasure of jumping out of an airplane, you know that at that speed, your ears are overwhelmed with sound--- the world is just a loud white-noise whoosh, with almost all sonic detail (other than you own whoops and screams) lost.

Perhaps this is a more-familiar analogy: Stick your head out your car window at normal highway speed of about 60 mph (100kph). If your head is fully out into the airstream, you won't hear much other than deafening wind noise. An EF2 tornado has winds twice that fast, and if you remember your basic physics, twice the airspeed is four times the power.

I can understand why people choose that "freight train" sound analogy: A nearby freight train is one of the loudest sustained white-noise sounds people commonly experience (especially in the midwest, where grade-level train track crossings are common). People latch on to that sound as a handy point of reference.

But I think comparing a tornado's noise to a freight train sells the tornado short. In the case of this EF2, for example, the noise was actually much, much louder than that. On top of the wind's own roar, you also have the sound of tens- or hundreds of thousands of trees breaking and falling, the sounds of tens of millions of tree limbs snapping. That's an unimaginable noise--- not only beyond what our ears can capture but way beyond what our brains can process.

People say "freight train sound" because they have no better reference. I said "continuous unusually sharp-sounding lightning" because I had no better reference.

I'd never heard a tornado destroying a forest before.

But the picture (above) brought it home, and I finally understood what I'd been hearing.

Ok, let's get back to the motorcycle ride through the tornado's path: that's tomorrow's entry!