YOSEMITE, Calif. – The photos were as stunning as they were absurd two months ago: Yosemite National Park buried under 15 feet of snow, homes in Mammoth Lakes stuck with snow depths higher than their roofs, and some ski resorts with so much snow that you could barely see the tops of 35-foot-tall ski lifts.
Now those regions are about to deal with the opposite issue: Too much sunshine and warmth, which is adding an unwelcome boost to the springtime snowmelt process and threatening to overwhelm the region’s rivers and streams.
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Flood Watches are now in effect starting in the middle of the week and lasting into at least the start of May for much of the Sierra Nevada as temperatures zoom about 10 to 20 degrees above average. The areas of Reno, Tahoe, Yosemite Valley, Yosemite National Park outside the valley and Mammoth Lakes – all areas with plenty of winter snowfall – are included in the watch.
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The warming trend was just getting started Tuesday in California, with highs already pegged to reach into the lower to mid-80s in the inland areas.
But as a ridge of high pressure strengthens along the West Coast, temperatures will likely reach their highest levels of the season later in the week. In the San Francisco Bay Area, temperatures in the city could reach the upper 70s, while upper 80s to near 90 degrees is likely in the warmer East Bay areas.
The warmth spreads into the Sacramento and San Joaquin valleys, with highs in Sacramento and Hanford expected in the lower to mid-90s from Thursday through Saturday.
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Even the Pacific Northwest gets in on the heat, with highs reaching the mid- to upper 70s around Seattle and mid-80s around Portland – both far and away their warmest temperatures of the year so far.
Up in the Sierra, temperatures will reach into the 50s through the 70s, depending on elevation. The FOX Forecast Center predicts highs in the mid-70s for Yosemite Falls this week, just two months after parts of Yosemite National Park were buried in 15 feet of snow and were forced to close for over three weeks.
“The concern being this warmth is going to make it into the higher elevations, where we have a pretty decent-sized snowpack,” FOX Weather meteorologist Marissa Torres said.
But it’s not only that the rivers will be running high and fast from the melting snow – they’ll be quite cold with the freshly melted snow, leaving officials concerned people will seek relief from the heat by jumping or perhaps falling into dangerously cold waters while boating or rafting.
“As unpredictable as water can be, it is very attractive this time of year,” said FOX Weather Meteorologist Amy Freeze. “People are going to want to get near it (and) this is going to be a season where we will have catastrophes because people get too close to this fast-flowing water and they didn’t expect (the chill) when they get inside (the water) or get too close to it.”
The National Weather Service in Reno, Nevada, warned that with water temperatures only in the 40s and 50s, loss of dexterity can occur in just five minutes, while even strong swimmers will lose muscle control in 10 minutes.
But 20% of those who fall or jump into cold water die in the first 60 seconds due to cold-water shock.
“Wearing a life jacket will significantly increase the chances of survival,” NWS Reno forecasters said.
This summer preview returns to more springlike weather next week as the ridge of high pressure fades and temperatures drop closer to more typical early-May readings, perhaps even drifting a bit below average again across the West.