July 6, 2005
There were many reports Tuesday night from people who say they saw a tornado. Today the National Weather Service was out surveying the damage, and they're not so sure.
The storm that hit Tuesday was barely the size of Charlottesville and lasted only a few minutes, but it left behind a path of destruction.
Steve Zubrick with the National Weather Service traced this path looking for evidence of what many people say they saw, a tornado.
"It looks like you would take an egg beater and would just take the tops of the trees and just churn them," described Zubrick of trees after a tornado.
The trees did not look this way to him. But they did look like they were hit with winds up to 70 mph from what he describes as a "wet micro-burst."
"What this is, is essentially you have a thunderstorm and there's a strong updraft that holds a core of heavy rain [aloft. Then the updraft weakens]," explained Zubrick. "And the core comes down to the surface and all of that rain basically just splashes down to the surface and spreads out in all directions."
This spreading out in all directions can be detected by looking at the damage. If the damage is created by winds in coming from different directions, then it is likely a tornado did not pass through. In the case of yesterday's storm, while some parts of the city had damage from winds directing west, other damage was from winds directing elsewhere. A divergent path like this indicates a micro-burst.
A tornado would be more pathlike. "I'm finding that there is more scattered damage over a much wider area and that is consistent with a down-burst," said Zubrick.
But this does not mean tornado-sighters were hallucinating. Micro-bursts do sometimes have what Zubrick calls "little eddies," that form on their edges.
"You do have a swirling appearance; the winds may be going back a little bit to the west, [instead of spreading out to the north]," he explained.
Micro-bursts such as the one we experienced yesterday are common in this part of the country, although it is hard to predict when they'll occur.