What’s the biggest threat to Coloradans’ safety when spending time outdoors this summer? No, it’s not mountain lions, bears or even rattlesnakes.

It’s lightning.

Lightning strikes kill an average of 49 people every year in the United States. Colorado had 17 lightning fatalities between 2005 and 2014, behind only Florida with 47 in the same period, and Texas with 20.

“The biggest weather threat in Colorado is lightning,” said Jim Pringle, a meteorologist with the National Weather Service. Human lightning strikes have occurred on 14ers, of course, but also golf courses and even in downtown Denver.

“The one thing in common is they were outside,” Pringle said. If lightning is coming, the safest place to be is inside or in a hard-topped vehicle. Also, the weather service recommends staying indoors at least 30 minutes after the last lightning bolt is observed. While inside, stay away from corded telephones and all electrical applicances, including computers.

The National Weather Service office in Grand Junction has created a lightning potential index for this area.

It provides a forecast of lightning activity for the next 60 hours.

On Thursday, for example, Southwest Colorado had mostly a low risk of lightning activity, but the area on the Colorado-Wyoming border had a high risk.

Paul Frisbie, a lead forecaster at the National Weather Service office, has developed the program over the past 10 years.

Land-management agencies use the product to help decide when and where to send outside crews, Pringle said.

June 21-27 also is Lightning Safety Preparedness Week.