The warm storm will push snow levels in the Sierra Nevada to above 7,500 feet, resulting in the bulk of the snowfall at higher elevations. Lassen National Park and the highest peaks of the Sierra could see some snowfall, and snow levels could dip below 7,000 feet on Wednesday night if temperatures fall.
Wet and slick roads will be the main concerns for the mountains, Sacramento-based forecasters wrote in the weather service’s daily forecast discussion for inland Northern California.
Weather experts measure the intensity of atmospheric rivers on a scale from 0 to 5. This week’s storm could reach as high as a 5 in the Guerneville area before decreasing to a 4 over Marin County and then to a 3 for the San Francisco area, according to the atmospheric river scale modeling by the Center for Western Weather and Water Extremes at UC San Diego’s Scripps Institution of Oceanography.
When atmospheric rivers stall over an area, they can cause rivers to rise and create dangerous flooding.
Two Mission District residents work to open a clogged drain on Mission and 21st Streets in San Francisco on Jan. 10, 2023. (Beth LaBerge/KQED)
In 2022, a family of atmospheric rivers dumped so much rain over California that multiple levees crumbled from the weight and intensity of the water, destroying hundreds of homes and disrupting life for thousands of people.
Other strong atmospheric rivers have caused flooding in parts of cities like San Francisco.
Gass said the good news, as of now, is that while this week’s atmospheric river “is expected to be a little bit stronger,” it does not look like it will park anywhere over the region.
“That’s the reason that we don’t have any flood watches out,” Gass said. “We would, if it were to show signs of stalling, but we’re not seeing any of that.”