“The good news is that we have a big storm starting here through the weekend, and it will be a cold one,” said Andy Reising, water resources engineer in the department’s snow survey and supply forecasting unit. Reising said it should be a good snow producer, with heaps of powder expected at low and high elevations.

“We’re quite pleased to announce that that’s coming, and it will help get us toward average, maybe even above average, for the state,” he said.

Daniel Swain, a University of California, Los Angeles climate scientist, said he strongly encouraged people not to head up to the mountains for a powder weekend, given that road travel will be dangerous. The California Highway Patrol office in Truckee has already warned about expected long delays and road closures.

Additionally, Swain said, ski resorts will probably need to halt chairlifts during strong winds.

The strong storm may come as a bit of shock to the Lake Tahoe area, “given how anemic this year’s snow season has been thus far at lake level,” Swain wrote in a blog post. “But this one looks like the real deal. ... This is virtually guaranteed to be a dangerous and disruptive snowstorm.”

Swain added in a briefing Thursday the storm could set top-five daily or two-day snow accumulation records in some locations. Snowfall rates of 2 inches per hour — or even up to 5 inches per hour — are possible for multiple hours on end, he said.

“The big story is going to be the Sierra Nevada and some of the other higher mountains in Northern California and in Central California … where there will be legitimate blizzard conditions developing later” Thursday night into Friday, Swain said during the briefing.

He noted the storm is somewhat unusual for its frigid temperatures and wet conditions.

“We rarely get air masses this cold that are also this moist and associated with this much storm activity,” Swain said. “We definitely get colder air masses than this one in California, but they’re usually much drier than this one.”

The National Weather Service issued a blizzard warning over a wide swath of the Sierra Nevada, from Lassen Volcanic National Park in Shasta County to Kings Canyon National Park in Fresno County. The blizzard warning began on Thursday and lasts through Sunday; the worst of the storm was expected between Friday afternoon through the midday of Saturday.

“For Sierra locations, don’t get caught up in the ‘worst conditions’ time frame. It is going to be really bad throughout the entire event!” the weather service office in Reno warned. “Winds ... will remain strong enough to produce near-zero visibility in the Sierra and the foothills.”

The weather service office in Eureka warned of snow on all roads 1,000 feet above sea level between Thursday through Saturday.

Highway 101 at Ridgewood Summit in Mendocino County could get half a foot of snow. And Highway 101 at Prairie Creek Summit in Humboldt County could get 1 to 1.5 feet.

Hail could strike coastal roads in Humboldt and Del Norte counties on Friday and Saturday, and linger, forecasters said. “Ease off the gas if you suddenly find yourself on a hail-covered roadway,” the weather service said. “Do not slam on the brakes. Avoid overcorrecting.”

There’s a chance of up to 1 inch of snow on the Grapevine section of Interstate 5, which connects Los Angeles County with the Central Valley through the Tejon Pass. Snow is also possible on Highway 58 over the Tehachapi Pass, which connects Bakersfield with the Mojave Desert.

In the mountains of San Diego, Riverside and San Bernardino counties, there could be 3 to 7 inches of snow at areas 7,000 feet above sea level, and 1 to 3 inches at areas between 6,000 to 7,000 feet.

In Los Angeles County, areas at 7,000 feet above sea level could see 5 to 10 inches of snow, and areas 4,000 above sea level could see at least 1 inch.

There’s a slight chance of rain in L.A., Orange and Ventura counties during the day Friday, a probability that grows on Friday night. Rain is expected during the day Saturday in those coastal counties as well as the Inland Empire.

From Friday through Sunday, downtown L.A. is expected to get 0.41 inches of rain; Long Beach, 0.34 inches; Redondo Beach, 0.29 inches; Santa Clarita, 0.51 inches; Pomona, 0.58 inches; Oxnard, 0.34 inches; and Santa Barbara, 0.48 inches.

Anaheim could get up to half an inch of rain; Irvine, San Clemente and Riverside, up to 0.4 inches; Ontario, up to 0.7 inches; San Bernardino, up to 1 inch; and San Diego, up to 0.2 inches.

The San Francisco Bay Area is forecast to see rain and winds Thursday through Saturday, with 0.5 to 2 inches of precipitation expected in the cities. Snow is possible on the Bay Area’s highest peaks.

Strong gusts from 35 to 55 mph are a concern in the section of the Sacramento Valley that is north of Marysville, the county seat of Yuba County.

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