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Friday ó May 7, 2004

News

Wanted: Weather spotters

Severe weather workshop focuses on Idaho


By GREG STAHL
Express Staff Writer

Since the 1940s, the National Weather Service has been nurturing a civilian weather spotter program to help the agency more accurately alert the public at large when hazardous weather is imminent.

On Wednesday, May 5, National Weather Service Warning Coordination Meteorologist Vernon Preston hosted a workshop in Bellevue to train a half dozen potential weather spotters.

"Itís a volunteer network, and all it takes is a 30-second phone call," he said. "Anybody can be a weather spotter, whether they get formal training or not. Weather spotters hold up the entire structure."

Hereís how it works: When severe weather occurs, weather spotters telephone the National Weather Service to relay on-the-ground observations that meteorologists then plug into computer models or logbooks. Sometimes weather spotter observations are used to alert people who are down-wind from an oncoming storm about the potential hazard.

Preston said severe-weather-related deaths are on the decline, and he credited the weather spotter program for that trend.

There are some 600 amateur weather spotters in Southern Idaho. There are about 120,000 throughout the U.S.

"Itís just real-time weather information," Preston said. "Itís just a great way to share in the community, and hopefully some folks will be saved from disaster."

Preston, who worked chasing severe storms on the Great Plains before moving to Idaho, gave an informative and interesting two-hour presentation on severe weather. He covered floods, snowstorms, thunderstorms and tornadoesóall hazardous weather that can and do occur in Idaho.

His class, by design, was an introduction to severe weather in the Intermountain West.

The United States has the most severe weather of anywhere in the world, Preston said. Idaho, compared with many states, is relatively mild. Each year, Idaho has about six tornadoes and a handful of severe hail or thunderstorm events.

By far, Idahoís most prevalent dangerous weather is caused by winter storms.

But it takes more than a thunderstorm or snowstrom to generate severe weather. Wind is not considered severe until is reaches 60 mph gusts or is sustained at 40 mph. Snowstorms are considered severe if they pile higher than 6 inches on the plain or higher than 9 inches in the mountains within a 24-hour period.

"But when you throw wind in to the equation, any snow can be dangerous," Preston said.

Ice storms are considered severe when they accumulate to a quarter of an inch or deeper.

The lionís share of Prestonís presentation focused on thunderstorms and the ingredients that go into forming one. He explained updrafts, downdrafts, overshooting tops, rain-free cloud bases, wall clouds and microbursts.

Though Preston explained a lot of the reasons weather becomes severe, he admitted that there are things science canít yet explain.

"We just donít know certain reasons why storms become severe," he said.


Weather spotter basics

In Southern Idaho, weather spotters should call (800) 877-1937 when they discover severe weather. Here are some rules of thumb when gauging whether weather is severe or not:

  • Tornadoes (location and movement).
  • Rainfall amounts (over 1 inch).
  • Damaging winds (estimate speed).
  • Low visibility (less than one half mile).
  • Freezing rain.
  • Snow totals (more than 1 inch per hour).
  • Hail (dime size or larger).
  • Flooding.

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The Idaho Mountain Express is distributed free to residents and guests throughout the Sun Valley, Idaho resort area community. Subscribers to the Idaho Mountain Express will read these stories and others in this week's issue.





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