THE VIRGINIAN-PILOT
Copyright (c) 1994, Landmark Communications, Inc.
DATE: Saturday, August 20, 1994 TAG: 9408200251
SECTION: LOCAL PAGE: B5 EDITION: FINAL
SOURCE: ASSOCIATED PRESS
DATELINE: ROANOKE LENGTH: Medium: 65 lines
Tornadoes are relatively rare in Virginia, with most counties having been hit by fewer than four in the past four decades.
The mountainous terrain of western Virginia stops most from forming, which made the twister this week in Henry County particularly unusual, weather experts said after the disaster.
The tornado Wednesday was only the second recorded for the county, which is on the eastern fringe of the Blue Ridge Mountains.
The same peaks that provide breathtaking views also break up the circular weather patterns that spawn tornadoes, said Chip Knappenberger, a climatologist at the state Climatology Office in Charlottesville.
Would-be twisters that might wreak havoc on smoother terrain tend to spin out and dissipate over uneven landscapes, he said.
From 1953 to 1990, 240 tornadoes hit Virginia. Chesterfield County had the most, with nine, followed by Fairfax County with seven and Virginia Beach with six. In the western mountains, most counties have had no recorded tornadoes since 1953 and a dozen have had just one each.
The mountains don't necessarily stop tornadoes from developing - the funnels form up in the clouds - but they do reduce touchdowns, Knappenberger said.
The numbers may be a bit skewed because recording tornadoes in sparsely populated, mountainous terrain is a bit more difficult than in the flat Midwest, he said.
``If a tornado happens in Kansas, someone's going to see it,'' Knappenberger said. ``It's hard to see very far in the mountains.''
Because a tornado has to be verified by the National Weather Service to be counted, the actual numbers of hill-terrain twisters may be somewhat higher than the published figures, Knappenberger said.
Weather service verification doesn't require funnel-cloud sightings but is based on damage surveys conducted after the storm passes, said Rich Kane, a meteorologist at the new weather service station in Blacksburg.
Kane said the Martinsville twister presented a classic example of tornado damage: a clear-cut path, evidence of counterclockwise winds, twisted trees, rocks hurled through windows.
Although a tornado watch issued Tuesday night by the Severe Storms Forecasting Center in Kansas City covered the Henry County area and gave Martinsville residents some warning, predicting tornadoes with conventional radar systems is difficult, if not impossible, Kane said.
A new Doppler radar system scheduled to be operating in Blacksburg by February will improve dramatically the ability to predict twisters, he said. Unlike conventional radars, Doppler systems show the rotation as well as the intensity of storms, making it much easier for meteorologists to pinpoint funnel clouds.
Right now, the nearest Doppler systems are in Sterling and Wakefield, both just out of range of Martinsville. If the Blacksburg radar had been up and running early Wednesday, the Weather Service easily could have predicted the Martinsville tornado, Kane said.
As it was, the storm that spawned the twister appeared no more ominous than any other storm cell on the conventional radar screen, he said.
KEYWORDS: TORNADOES by CNB