SACRAMENTO (CBS13) — Temperatures have dropped nearly 40 degrees in some areas across the region since Friday.

What’s behind this wild swing in spring?

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There is snow in the Sierra, and there is wind and rain in the valley. What a difference three days make.

Rewind to Friday, Drone13 captured cyclists braving the heat along the American River.

Then on Saturday, whipping winds and valley temperatures brought the earliest spring wildfire warning in California history.

Now, two days later, the summit has received so much snow, a crash closes down I-80 at Donner Pass.

And by Monday night, snow is expected to fall as low as 4,000 feet.

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“Here in California, we’re now in a climate where we’re likely to get hot dry periods punctuated by extreme wet conditions,” said climate expert Dr. Noah Diffenbaugh with Stanford University.

We asked Dr. Doffenbaugh if weather whiplash is consistent with climate change.

He said, yes.

“What that means is we’re more likely to have heat waves in the fall, winter and spring,” he said. “Our snow is much more likely to melt earlier in the year, and then in the summer.”

Monday’s weather was a welcome sight for firefighters, but Cal Fire said this new normal means staying nimble.

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“We don’t really look at it as a fire season anymore,” said Jonn Heggie with Cal Fire. “It’s a fire year.”