A lightning warning system? One forecaster is working on it.

A NWS forecaster based in Colorado is refining his Lightning Potential Index, to help local outdoors enthusiasts gauge their exposure to strikes. Here's how it works – and why it wasn't available to two hikers killed over the weekend.

Brennan Linsley/AP
A storm gathers over Rocky Mountain National Park just west of Estes Park, Colo., Monday, July 14, 2014. Two fatal lightning strikes on consecutive days the previous weekend pinpoint dangers not always apparent to visitors to the 11,000-foot exposed high country of the park. Afternoon storms visible miles away can arrive overhead suddenly.

The tragic deaths of two hikers in Colorado's high country and injuries to at least a dozen others – all due to lightning strikes – drive home the need for vigilance among outdoor enthusiasts during periods of unstable summer weather.

To that end, the National Weather Service office in Colorado is endeavoring to fill that need, holding awareness campaigns and developing an experimental Lightning Potential Index to help residents in the western one-third of the state safely plan their outdoor activities.

The campaigns and the index, say officials, are helping to reduce the number of lightning-related fatalities in the state. Colorado, home to perhaps the best hiking country in America, ranked No. 4 in the nation for lighting-related deaths since 1959 – before the trend changed.

“We average three lightning fatalities each year,” said Robert Glancy, warning coordination meteorologist for the National Weather Service in Boulder, Colo. “On average, it is the No. 1 thunderstorm hazard. Some years flash flooding is the No. 1 hazard, but most years it is lightning.”

Lightning-related deaths are declining for the nation overall, as well, as awareness of the danger grows. In 2009, there were 34 deaths. Fatalities steadily declined since then, dropping to 23 in 2013, says Mr. Glancy.

Alas, the Lightning Potential Index did not cover the part of the state where the fatal bolts struck in recent days. 

On Friday, Rebecca Teilhet of Yellow Springs, Ohio, who was hiking the stunning Ute Crossing Trail with her husband in Rocky Mountain National Park, was killed by a lightning strike when a fast-moving thunderstorm moved into the area. The next day, Gregory Cardwell of Scottsbluff, Neb., was killed instantly in the same vicinity after being struck by lightning as he stood at a pullout on the park's Trail Ridge Road, at 10,800 feet above sea level. 

The weather service's Lightning Potential Index is the brainchild of Paul Frisbie, a lead forecaster who began developing the tool in 2010 to alert the local public to lightning dangers. It was upgraded in March, then announced to the public on July 10. It went live online one day before the first deadly lightning strike of the season.

So far, it is contained to western Colorado.

"We are still continuing to refine it, so before another [National Weather Service] office decides to adopt it, they want to see if it will work for them as well," says Mr. Frisbie. "If it proves valuable, then perhaps other offices will adopt it, but right now it is forecast-specific, so it's only in Grand Junction, [Colo.,] eastern Utah, and western Colorado, but not Rocky Mountain National Park or anywhere else in the country."

The index consists of an online map that shows four levels of lightning risk: low, moderate, high, and extreme. The local NWS meteorologists check it every three hours to see if it needs updating. 

Glancy describes the index as "a planning tool" that helps outdoors enthusiasts "gauge their exposure for deadly lightning.”

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