When is lightning likely?

The National Weather Service’s new lightning potential index.


On average, lightning kills about 50 people every year in the United States. This year so far, 19 have died, five in Western states. Two were in Colorado’s Rocky Mountain National Park — a woman hiker and a man sightseeing at an overlook. Other deaths include a swimmer at Venice Beach, California, a man in an Arizona desert, and a cyclist in New Mexico. Lightning can strike anywhere — and does indeed hit the same place twice — but the National Weather Service is developing a “lightning potential index” that it is testing for western Colorado and eastern Utah before expanding. The index will track the conditions likely to cause strikes over a 60-hour period and be updated every three hours with computer modeling. Its developers hope that it will help protect people, but remember: Lightning by its nature is highly unpredictable, and the index but a guide.