The big melt is upon us.

Weather forecasters and climate scientists expect an early season heat wave by midweek across California that will likely cause flooding as snow melts, especially along rivers in the southern Sierra Nevada, where there is still a record amount of snow layered on the mountain range, said UCLA climate scientist Daniel Swain.

“It is looking like this week is going to be an exclamation point on this melting process,” he said.

Swain said the heat could bring further disruptive flooding in the Tulare Lake basin, where an inland lake has appeared, drowning farmland and threatening cities.

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“This week is just going to get progressively worse and then maybe relent a bit the following week,” he said. “The problem is there’s nowhere else for this water to go and the Tulare Lake basin is just going to fill up like a bathtub.”

The snowmelt is expected to speed up into the weekend and into next week. Swain said there is no indication of any atmospheric rivers in the forecast that could add to or further melt the snowpack.

“Of course, it isn’t all going to melt this week,” he said. “The snowpack in some parts of the southern Sierra will remain through mid-summer and will be melting for months.”

Flooding is also expected on the Merced River up into Yosemite Valley, but will likely be less in other watersheds in the middle or northern Sierra.

“There is still a record amount of snow water that is yet to come down the mountain, and it all has to come down at some point,” he said.

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Swain said the flood risk across the Central Valley, but particularly in the southern part of the range, will not go away anytime soon and there’s a growing likelihood that next winter will also be a wet season. He said that just how wet the upcoming winter will be will depend, in part, on how strong El Niño is during that time; he notes predictions will become more evident this summer.

[pullquote size="medium" align="right" citation="Daniel Swain, climate scientist, UCLA"]‘A strong or extreme El Niño event next winter would raise the odds of another unusually wet winter in some parts of California. That is a real possibility we should be thinking about right now.’[/pullquote]

“A strong or extreme El Niño event next winter would raise the odds of another unusually wet winter in some parts of California,” he said. “That is a real possibility we should be thinking about right now.”

But the aftereffects of a wetter-than-normal winter aren’t all negative. Swain said there’s a likelihood that the soils at higher elevations remain saturated into next winter, decreasing the possibility of wildfires seen in previous years that burned hundreds of thousands of acres near alpine towns like South Lake Tahoe.

The record levels of snow, he said, mean the forest floor will likely be painted white for the first portion of the wildfire season.

“This is one reason why I think that the high-elevation fire season will be significantly attenuated this year,” he said. “It’s a different story at lower elevations because we had a lot of extra vegetation growth that is still going to dry out this summer.”

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