Heavy rains passing across the western slope of the Sierra Nevada prompted a flash-flood warning from the National Weather Service on Saturday and sent mud and debris onto rural roads in areas burned by the Butte fire in Amador and Calaveras counties.
The storms resulted from a low-pressure trough that dumped nearly 2 inches of rain in some parts of the foothills and sparked lightning in the Sacramento area starting at about 2 a.m. Saturday, said Travis Wilson, a meteorologist with the National Weather Service in Sacramento.
Heavy rains had also drenched higher elevations of the Sierra Nevada on Friday, giving way to periods of sunlight and rainbows as clouds parted and reformed. Such intermittent rains can allow warming that intensifies storms, Wilson said.
“You get surface heating when it’s not totally socked in with a cloud layer, and you’re able to get thunderstorms,” the meteorologist said. “It provides more lift.”
Clouds cool as they rise, water condenses and rain falls, he said. On Saturday morning it fell heavily enough in a short period of time to prompt the flash-flood warning, he said.
The warning was for parts of Placer, Amador, El Dorado and Calaveras counties as well as northeastern San Joaquin county. There were fears of debris flows and mud slides near steep terrain.
The 71,000 acres scorched by the Butte fire lay in the storm’s path.
That fire broke out Sept. 9 in neighboring Amador County and ranks among the 10 worst in state history. It killed two residents and destroyed 475 homes. The cause remains under investigation.
As residents of the largely rural area resume their lives and start to rebuild, the possibility of mudslides is a prime concern, especially with stronger El Niño rains predicted this winter.
There were no injuries or damage reported from Saturday’s slides. One mudslide temporarily closed a portion of Electra Road along the north fork of the Mokelumne River in southern Amador County, near the origin of the Butte fire. The road has since been cleared, the Amador County Sheriff’s Office said.
Another slide sent branches and debris onto Highway 26 in Calaveras County, Wilson said.
For Saturday night and Sunday, the National Weather Service is predicting a 30 percent chance of showers in the area of the Butte fire. Skies should clear this week, Wilson said.
“The trough will lift up and out,” he said. “It’s heading off to our east.”