Powerful thunderstorms swept across a wide stretch of East Idaho on Saturday night, prompting a flash flood warning and bringing large hail, damaging winds and deadly lightning to several local communities.
Around 9:45 p.m. Saturday the National Weather Service issued a flash flood warning for parts of Blaine, Bingham, Butte and Power counties, in effect until 12:45 a.m. Sunday.
Forecasters said heavy rain, with rates of 1 to 2 inches per hour, has already produced ongoing or imminent flash flooding in the warned area, including near Craters of the Moon and Big Southern Butte. The warning covers flooding risks to small creeks and streams, urban areas, highways, streets, underpasses and other low-lying or poorly drained areas.
"Turn around, don't drown when encountering flooded roads," the weather service warned. "Most flood deaths occur in vehicles."
Minutes later, the weather service issued a special weather statement warning of even stronger winds moving through parts of Jefferson, Butte, Bonneville and Bingham counties through 11 p.m. Saturday.
Radar tracked a line of strong thunderstorms extending from near Idaho National Laboratory to Atomic City to Rockford, moving east at 10 mph and carrying wind gusts of 50 to 55 mph — among the strongest winds reported so far Saturday.
Forecasters warned the gusts could knock down tree limbs and blow around unsecured objects in Blackfoot, Firth, Rose, Rockford, Moreland, Groveland, East Butte and several other areas.
Forecasters warned the thunderstorm threat could continue until midnight across East Idaho and more thunderstorms could develop on Sunday.
Earlier Saturday night, the weather service issued a severe thunderstorm warning around 9 p.m. for a storm tracked 15 miles southwest of Atomic City, moving northeast at 30 mph. The warning, covering parts of Blaine, Butte, Power, Bonneville and Bingham counties, cited quarter-size hail capable of damaging vehicles. The areas in the storm's path included Blackfoot, Atomic City, Rockford, Moreland, Rose, Taber, Groveland and East Butte.
Forecasters urged anyone in the storm's path to move to an interior room on the lowest floor of a building immediately, warning that large hail, damaging winds and continuous cloud-to-ground lightning were all occurring with the storm.
"Lightning is one of nature's leading killers," the weather service's warning stated. "Remember, if you can hear thunder, you are close enough to be struck by lightning."
Around the same time, the weather service issued a broader special weather statement covering an even wider swath of East Idaho, including eastern Blaine, southwestern Jefferson, northwestern Bannock, southeastern Butte, north-central Power, and northwestern Bonneville and Bingham counties. That alert tracked a line of strong storms stretching from near Craters of the Moon to south of Idaho National Laboratory, moving northeast at 35 mph and carrying wind gusts over 35 mph along with pea-size hail.
Forecasters warned the gusty winds could snap tree limbs and send unsecured objects flying, with minor hail damage possible to outdoor property. The areas at risk from these storms included Aberdeen, American Falls Reservoir, Fort Hall, Springfield, Pingree, Sterling and Butte City, among others.
The weather service issued a specific warning for anyone on or near American Falls Reservoir, urging boaters and swimmers to get out of the water immediately and move indoors or into a vehicle, as strong winds were expected to whip up rough, dangerous chop on the water.
"Do not be caught on the water in a thunderstorm," the alert warned.
The severe thunderstorm warning and the earlier special weather statement have since expired, though the flash flood warning and the newer high-wind statement both remain in effect.
Forecasters said the chance of additional thunderstorms across East Idaho would continue into late Saturday night, with another chance of thunderstorms returning Sunday after 2 p.m.
Multiple thunderstorms had already barreled through East Idaho on Saturday afternoon, but the ones arriving Saturday night appeared to be much stronger.
Residents across the region are urged to stay alert for additional warnings, monitor local forecasts, and be prepared to seek shelter quickly if storms redevelop.
Lightning remains a danger even after visible storms pass, forecasters noted, since it can strike as far as 10 miles from a storm's core. Anyone who hears thunder should move indoors and remain there until the threat has fully passed.