From the ABC 7 Weather team

Fog self-materializes inside Springfield, Mass. tornado (VIDEO)

June 2, 2011 - 04:53 AM
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The twister that hit Springfield, Mass., yesterday spread awful destruction but also left behind an eye-grabbing illustration of weird tornado physics.

The cold front that scrubbed away some of the heat in D.C. yesterday with torrential rain and hail produced even more startling effects north of town. Roof-tearing, car-flipping tornadoes were seen in several Massachusetts communities, and by the end of the storm there were reports of at least four people dead. Massachusetts is now in a state of emergency.

There will no doubt be many crazy weather videos popping up from yesterday, perhaps even some of other twisters throughout the country like the wraithlike "rope tornadoes" spotted in Dawson, Neb. But the video that caught the eye of ABC7's senior meteorologist Bob Ryan was the one you see after the jump. It shows a weak twister doing doughnuts in the Connecticut River in Springfield, about 90 miles west of Boston.

What's so interesting about this footage? At first glance it appears to show a typical waterspout. Despite appearances, though, that is not preexisting fog getting twirled up from the river into the funnel cloud like spaghetti onto a fork. It is water condensing right out of the air, thanks to the weird physical environment inside a tornado vortex. (If you can't see the video, here's another version.)

"The fog is not caused by the cooling of the air but by the pressure dropping," says Ryan. "In the vortex, it’s probably the same pressure as at cloud level. When the pressure drops it causes condensation."

The hungry vortex sucking up that vapor provides a perfect model for how fluids (including air, from a physics viewpoint) act inside a vortex. "It’s something you sometimes see with the flying debris or with water in a waterspout," says Ryan. "But this was pretty dramatic."

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