Warmer storm on tap later this week
Heavy rains and rapid snow melt could lead to flooding
Remnants from the most recent weekend winter storm are expected to bring more rains and snow at times to Calaveras and Tuolumne counties, prompting forecasters to issue another winter storm warning for the Central Sierra foothills and higher in the mountains through 10 a.m. Wednesday.
Precipitation through Wednesday morning could be limited to up to a halfinch more rain for Sonora and Yosemite National Park — which remained closed Monday with snow 15 feet deep in places — and 18 inches more snow at Ebbetts Pass on Highway 4, up to 8 inches at Sonora Pass on Highway 108, and 3 inches or less at Tioga Pass on Highway 120.
“This storm through early Wednesday is lingering from the weekend storm, and we’ll see showery activity on and off through Wednesday morning, bringing more rain and more snow at times,” Katrina Hand, a National Weather Service meteorologist in Sacramento, said Monday afternoon in a phone interview.
Later this week there is potential for a stronger, warmer storm with heavy rains — up to 5 inches for Sonora — and rapid snowmelt in the Central Sierra, which could bring flooding at elevations below 5,000 feet, forecasters in Hanford said in a hydrologic outlook message Monday afternoon.
“Late Thursday into the weekend is looking more like an atmospheric river type of storm,” Hand said. “A bit warm and wetter, so the snow levels will be a bit higher for the late week and weekend storm.”
The stronger storm system forming over the Eastern Pacific will approach the Oregon and California coast Thursday night and Friday, Hanford forecasters said. Overnight lows in the Sonora area could jump from 29
degrees Fahrenheit late Wednesday to the mid-40s late Thursday, Friday, and Saturday.
“An abundance of subtropical moisture will move inland over Central California along the southern periphery of this storm system Thursday night through Friday night,” Hanford forecasters said. “Mild air associated with this air mass will cause snow levels to rise to around 8,000 feet Friday. In addition, heavy rainfall and the mild air mass will result in snow melt in areas below 5,000 feet.”
In the Central Sierra foothills, including the Sonora area and Yosemite, 4 to 5 inches of rain is possible Thursday night through Saturday. The majority of this rain should fall Friday and Friday night. Ebbetts, Sonora, and Tioga passes all could receive 3 to 4 more feet of snow with the Thursdayto-saturday storm.
“Persons living near rivers and streams should closely monitor water levels and be ready to move to higher ground if the threat of flooding becomes imminent,” Hanford forecasters said. “If you live in a flood-prone area or near rivers and streams, now would be a good time to prepare and have an evacuation plan in place in the event high water becomes a threat to your safety.”
Impacts from the weekend storm included heightened concerns for Tuolumne County government employees and their families. County Administrator Tracie Riggs said she and the county Board of Supervisors decided to open county government buildings at 11 a.m. Monday.
“Snow accumulation begins around 2,500 feet in elevation and has caused massive power outages, trees have fallen on roads, homes and vehicles, and many individuals are stranded,” Riggs stated in an email distributed Sunday evening.
County road crews, deputies, Office of Emergency Services staff, and others have been working around the clock for almost two weeks straight to try to support residents and visitors who have been affected by the weather.
“Many of our employees have experienced significant snowfall at their homes, and many are without power,” Riggs said Sunday evening.
While some county buildings may be open Monday, “it is likely our offices will be scarcely staffed,” Riggs said. “We continue to ask for your patience and understanding as we work through the effects of this most recent storm.”
Calaveras, Tuolumne and Mariposa counties were declared droughtfree last week for the first time in three years.
Record-setting atmospheric river storms in late December and the first half of January, along with more recent colder storms packing low-elevation snow, sleet, and icy rains, have combined to reduce drought intensity in Calaveras and Tuolumne counties to “none,” according to U.S. Drought Monitor scientists.
As of Monday morning, 49 snowpack sensors across the Central Sierra showed average snowwater equivalence of 48.7 inches, 197% of normal for the date March 6. Statewide, 108 sensors up and down the Sierra Nevada range showed average snow-water equivalence of 46.5 inches, 192% of normal.
A five-station index including Calaveras Big Trees and Hetch Hetchy showed principal watersheds of Calaveras and Tuolumne counties had received 43.9 inches of precipitation since the current water year began Oct. 1 — 157% of average for the date March 6.