4 feet of snow, heavy rain, flooding all possible at Tahoe with incoming atmospheric river event
SOUTH LAKE TAHOE, Calif. — Snowfall will wind down on Wednesday and a warm atmospheric river packing heavy moisture will hit the Lake Tahoe Basin Thursday bringing feet of high elevation snow, an abundance of rain, possible flooding and more travel disruptions.
Forecasters are having a difficult time pinpointing snow levels with the incoming multi-day storm, but on Wednesday they are expecting 3 to 6 inches of snow for the East Shore of Tahoe and 6 to 12 inches along the Sierra crest generally north of U.S. Highway 50 and west of State Route 89 through early afternoon. Winds could also gust up to 75 mph along the Sierra crest.
For those driving at the lake Wednesday morning, chain controls are in effect all along the North Shore and throughout Truckee, according to nvroads.com, and also along the West Shore on SR-89. Emerald Bay on SR-89 is also closed to through traffic.
The National Weather Service in Reno has a winter weather advisory in place through 1 p.m. Wednesday.
For the multi-day atmospheric river rain on snow event, the weather service has issued flood and winter storm watches for the region that go into effect at 4 p.m. Thursday, March 9, and lasts through 11 a.m. Sunday, March 12.
The storm is bringing a massive amount of moisture including 6-8 inches along the Sierra crest, 3-5 inches in Sierra communities and 1-2 inches for far western Nevada communities.
The winter storm watch is for areas above 6,500 feet where heavy snow is likely. Overall, 8 to 20 inches of snow may accumulate except 2 to 4 feet above 7,000 feet. Winds along the Sierra crest will reach up to 120 mph.
“The lowest confidence factor in this storm … snow levels,” the service said. “The current, most likely forecast still indicates snow levels rapidly increasing overnight to around 8,000- 8,500 feet at the onset of heaviest precipitation overnight Thursday. Snow levels look to remain high through late morning Friday, before a colder upper-level low swings by to our north and surges cooler southward through Friday afternoon. Snow levels will then hover between 6,000-7,000 feet through Saturday.
“With that said, there are a few caveats to this forecast due to the potential for a deep isothermal layer for a short period late Thursday into early Friday morning as indicated by model soundings,” the service added. “This could drop snow levels 1,000-2,000 feet lower than forecast early in the event.”
Travel disruptions are likely in the mountains, especially over mountain passes.
With the rain at lower elevations, the service is warning that excessive, rapid runoff could result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Flooding may occur in poor drainage and urban areas due to deep snow confining flow and limiting drainage. Low-water crossings may be flooded. Storm drains and ditches may become clogged with snow and debris.
The service a couple of days ago said the deep snowpack will likely act like a sponge and retain much of the moisture generated by the storm, but are warning that continued precipitation may begin to pass rain through the pack with the prolonged event.
The heavy rain could also cause structural issues for homeowners by loading an already deep snowpack of roofs.
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