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How dry is it? Scientist says California has only slim chance of normal rainfall this winter

Fishermen are silhoutted against the setting sun at Royal Palms Beach on Los Angeles’ Palos Verdes Peninsula on Nov. 21, 2017. Many parts of California have experienced warm, dry weather so far this rainy season.
Fishermen are silhoutted against the setting sun at Royal Palms Beach on Los Angeles’ Palos Verdes Peninsula on Nov. 21, 2017. Many parts of California have experienced warm, dry weather so far this rainy season. TNS

This is how dry it has been so far this season: California’s chances of having a normal “water year” have fallen to around 33 percent in much of the state, according to a federal scientist.

Michael Dettinger, a hydrologist with the U.S. Geological Survey, said those dismal odds are based on the amount of rain and snow that has fallen so far this year – and the history of how much precipitation California traditionally gets in the remaining months of the rainy season.

red flag
As California’s dry December continues, the National Weather Service issued a “red flag” warning for this weekend in parts of Northern and Central California. A scientist puts the chances of a normal water year at 33 percent. National Weather Service

Dettinger said most of Northern California has either a 33 percent or 34 percent chance of having a normal water year. The chances drop to as low as 14 percent in much of the southern half of the state, where rainfall has been even scarcer so far this season. The water year runs from Oct. 1 to Sept. 30.

“We’ve got a hole that we’re developing, a precipitation deficit,” Dettinger said in an interview Friday. “We’re developing a hole that’s hard to get out of.”

Even if the season had been rainy so far, Dettinger said California would struggle to reach normal precipitation for the season. That’s because most California winters are on the dry side. The wet winters, while relatively rare, are so rainy that they generate the lion’s share of the state’s water supply.

Dettinger’s findings, reported on a blog run by UC San Diego’s Center for Western Weather and Water Extremes, come amid fresh signs of a difficult water year. Citing dry conditions and gusty winds, the National Weather Service on Friday issued “red flag” warnings signaling increased fire risks for much of the western Sacramento Valley and portions of the Bay Area. The warning is in effect until Sunday morning.

State officials and most forecasters have said it’s still too soon to predict how this winter will turn out, although they’ve acknowledged they’re increasingly concerned about the recent dry spell. Jan Null, who runs a private forecasting service called Golden Gate Weather Services, said the dry December “makes it harder to get to normal” for the full season.

Null, however, said one dry winter wouldn’t necessarily mean the drought has returned. Most of Northern California’s reservoirs are in good shape, thanks to last winter’s drought-snapping rains, giving the state a buffer if 2017-18 is short on precipitation.

“It takes several years of rainfall deficit” to create a drought, he said.

Although the weather service forecast a slight chance of rain or snow in the northern Sierra Nevada this weekend, the overall outlook remains dry for the next several days. There’s a chance of light rain or snow in the Sacramento Valley next Wednesday or Thursday.

Sacramento has received just 52 percent of its normal rainfall so far this season, and just 0.03 inches this month. Normally the city gets almost 3.5 inches of rain in December.

Dale Kasler: 916-321-1066, @dakasler

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