The heat is on in California. Temperatures reached the 90s in many valley locations Thursday and are forecast to do so again Friday and Saturday, challenging record highs in Sacramento, Redding, Red Bluff, Stockton and Modesto, among other cities.
As temperatures hover 15 to 20 degrees above normal across much of the state, flooding is possible into early next week as mountain snow melts and rivers rise. After an onslaught of atmospheric rivers and other storms since December, the state snowpack is 260 percent of normal and still not far off its record-setting peak one month ago.
Flood watches are in effect through Monday morning for much of the Sierra Nevada, including the Lake Tahoe area, due to the likelihood of strong snowmelt near and below 8,000 feet. The concern is not just for flooding, but also for those who might be enticed to cool off in the water.
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“Creeks and streams will be running high and fast with minor flooding impacts along several mainstem rivers as well. The water will be extremely cold, quickly causing shock,” the Weather Service wrote. “Low-water crossings may be flooded and riverbanks may become unstable. Nuisance flooding may also occur where drainage systems are impeded by snow or clogged by other debris.”
Water temperatures are in the 30s to 50s, which is considered too cold for swimming. The National Weather Service in Reno tweeted that “roughly 20 percent of those who fall in cold water die in the first minute of immersion due to cold water shock.”
Where flooding is possible
Flooding is of particular concern in the area around Yosemite National Park, which will be closed from Friday night until at least Wednesday.
The National Weather Service has issued a flood warning for the Merced River at Pohono Bridge within the park, where minor flooding is expected. The river is forecast to rise above its flood stage of 10 feet just after midnight Friday, before peaking at about 11 feet early Sunday morning.
“At 10.0 feet, Western portion of North Pines Campground located at the east end of Yosemite Valley between the confluence of the Merced River and Tenaya Creek begins to flood. Water rises to the base of the swinging bridge downstream from Chapel Meadow,” the Weather Service wrote.
Minor flooding is also forecast along the Forks of the Carson River, which is forecast to reach near or just past its flood stage of 13.5 feet at Woodfords, south of Lake Tahoe near the Nevada border starting Saturday night and along the Walker River near Mason, Nev., on Monday. The “mainstem Carson near Carson City, West Walker, and Susan River should also be monitored very closely over the next several days,” the Weather Service wrote.
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Fresno, Kings and Tulare counties in Central California are under a flood warning “until further notice” due to flooding caused by a dam release.
Share this articleShare“A more serious situation continues to evolve in and near the Tulare Lake Basin, since the rate of inflow into an already flooded area will spike later this week — causing yet more problems, though the details remain somewhat hard to predict,” said Daniel Swain, a UCLA climate scientist, in an online update Wednesday. “There are vast tracts of agricultural land, as well as multiple small to medium-sized towns in the area, which will be exposed to a continually escalating flood threat for weeks to come.”
Brett Whitin, a hydrologic forecaster with the California Nevada River Forecast Center, said that some of the rivers that flow into the Tulare Basin have been steadily rising every day over the past week. Flows will peak on April 30 at about three times what they were on April 20.
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However, during dry weather in recent weeks, reservoir operators “have made enough space to handle the volumes that are looking to come in during the warm-up period,” he said.
Cooler weather next week to lower flood risk
The current heat wave and flood risk should be relatively short-lived. High temperatures across portions of the state are forecast to drop to as much as 10 to 15 degrees below normal, with valley highs only in the 60s and 70s, by Monday, and should remain in that range through most of next week.
The next chance of precipitation for California comes next week, mainly Tuesday through Friday, with areas of light to moderate rain and mountain snow possible. That could bring back the potential for minor flooding, but the threat of heavier flooding is expected to hold off until later in the season.
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“Because of the flip to cooler conditions, [the California Nevada River Forecast Center] is now projecting to have more of the snowmelt in June rather than May,” said Deirdre Des Jardins, an independent researcher and director of California Water Research. “That will be really helpful for management of the reservoirs.”
While cooler weather is expected for at least the first part of May, it’s a long melt season and flow forecasts are subject to change with changing temperatures.
Jason Samenow contributed to this report.
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