This weekend’s warm weather — with daytime temperatures in the upper 50s to lower 60s across the Sierra Nevadas this weekend — could accelerate the melting of the record-breaking snowpack and bring high river flows in the region.
California measured 235% of the average snowpack on April 1, which is the state's typical yearly peak for snowpack, according to the Sacramento Bee. And the southern Sierra in particular has three times as much snow as usual, a record amount, according to California's Department of Water Resources.
With temperatures 🌡️☀️ warming above average into next week, we are expecting snowmelt ❄️and resulting river flows to begin increasing. Here are our deterministic and ensemble forecasts at a few #Sierra 🏔️basins showing the potential for higher river flows. #CAwx #CAwater #CAsnow pic.twitter.com/hy8r2njoiF— NWS California-Nevada RFC (@NWSCNRFC) April 20, 2023
Some of the snow in the 6,000-to-8,000-foot elevation band in the mountains is already melting, the Chronicle reported.. But the worst is yet to come: Benjamin Hatchett, atmospheric sciences professor with the Desert Research Institute, told the Chronicle that snowmelt occurs quickest when it’s both warm and sunny.
UCLA climate scientist Daniel Swain also told the Chronicle he expects to see such conditions this weekend. Swain said that more than 90% of the snowpack atop the Sierra Nevada has yet to melt, so these conditions could mean that the rate of snowmelt would escalate rapidly.
Hatchett believes that overnight temperatures and cloud cover will remain cool enough this weekend to prevent rapid snowmelt, but that next week will see warming to those levels.
As the snow melts, the regions along rivers from the western slope of the Sierra Nevada, particularly the southern Sierra, are at high risk of flooding, according to the Chronicle. Other areas that could flood during the snowmelt season include the San Joaquin Valley and the Tulare Lake, as well as Owens Valley and other rivers south of Yosemite. The Merced River and the west fork of the Carson River could also reach flood stage in early May.
The Sierra Nevada snowpack above 8,000 feet is reportedly expected to melt in May and even early June, which could potentially bring even more flooding.
Swain told the Chronicle that people should expect this year’s snowmelt — and the flooding that could accompany it — “to be a very prolonged event.”
The silver lining for the Bay Area: There is no reported flood risk locally, as there has been no snowpack accumulated here.
READ MORE: Sierra Snowpack April Measurement One of the Deepest Recorded In 80 Years [SFist]
Feature Image via NASA Earth Observatory.