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The National Weather Service issued a flood watch early Tuesday for a large swath of the Sierra Nevada as thunderstorms continue to bring brief yet heavy bouts of rain to the mountain range straddling California and Nevada.
The watch is in effect through 9 p.m. Tuesday and includes the following California regions: the greater Lake Tahoe Area, eastern Lassen and eastern Plumas counties, Sierra County, Mono County and Surprise Valley. In Nevada, the Tahoe area, the greater Reno-Carson City-Minden area, Mineral and southern Lyon counties and northern Washoe County are all under the watch.
Just after 2 p.m., the weather service issued a more severe flood advisory for the east Dixie and Beckwourth burn scars, including Frenchman Lake and Frenchman, Big Cove and Spring Creek campgrounds. It’s in effect through 3:45 p.m.; the agency warned that flooding and debris flows could occur. Dawn Johnson, a forecaster with the weather service, specified that this area is east-northeast of Portola in Plumas County, west of Highway 395.
California has been in what forecasters call a “troughy weather pattern” with troughs of low pressure moving across the region. While ridges of high pressure are associated with warming and clear skies, troughs of low pressure bring cooler temperatures and cloud cover.
“We basically have a trough just sitting over the West right now, so we’re seeing continued moisture develop, which leads to thunderstorms in the mountains, basically every afternoon and evening,” Johnson said.
California has been stuck in the pattern for more than a week, with thunderstorms developing in the Sierra daily.
“They are slow-moving,” Johnson said. “They are heavy rainmakers, but they are not lasting very long.”
Johnson said these storms are of particular concern after the unusually wet winter. Soils are saturated and waterways are rushing, so it takes less rain than usual to cause flooding.
“If we see that heavy rain move into an area like a burn scar, areas where the creeks and streams are already full, then that brings us concern,” she said.
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