How the Arctic blizzard to bury Tahoe differs from previous storms

How the Arctic blizzard to bury Tahoe differs from previous storms

The National Weather Service expects 13 feet or more of snow to fall on the Sierra Nevada's highest peaks Thursday through Sunday.

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to update: Tahoe Blizzard: This is when snow and high winds are most dangerous

A severe winter storm will create blizzard conditions in the Sierra Nevada Thursday through Sunday. Snow could reach up to 13 feet in some locations. Mountain travel will be “extremely dangerous to impossible,” according to the National Weather Service, as strong storms and heavy snowfall could lead to periods of near-zero visibility.

“Travel should be limited to emergency situations only,” read the weather service’s blizzard warnings.

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Meteorologists say this storm is different from other storms this winter so far, in that it is heading directly from Alaska to California. A strong jet stream is expected to push the system inland toward the Sierra Nevada, where extreme snowfall rates of 2 to 5 inches per hour are expected for 48 to 72 consecutive hours.

If all goes well, the storm could deliver historic snowfall in the Sierra Nevada, including UC Berkeley's Central Sierra Snow Laboratory in Soda Springs (Nevada County) at 6,894 feet.

“If the forecast is correct, we have a real shot at beating the Snow Lab's daily snowfall record,” Andrew Schwartz, the lab's chief scientist and director, said in an email. On February 3, 1989, the current record, 52 inches of snow fell.

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Alaska water

The incoming storm is colder than the one that arrived earlier this winter, and is heading toward California from the frigid Gulf of Alaska. When cold winds blow over the Pacific Ocean, heat and moisture from the warm water rise and cool, condensing into ice clouds.

Other storms in California this winter have taken a direct line from Hawaii to the West Coast, a weather pattern characteristic of El Niño. From December through mid-February, systems stalled and swung off the California coast, bringing historic rains to Santa Barbara, Los Angeles and San Diego.

But the warm Pacific waters off California tore through these storms, which depend on cold air to survive, as they moved toward the Sierra Nevada.

“This led to storms that were in some sort of transition phase, which split new centers of movement…as they encountered coastal and inland areas,” meteorologist Heather Richards said.

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A Caltrans snowplow clears snow from the road below Echo Summit in Myers, California.
Skiers and boarders wait for the opening of the Heavenly Gondola in South Lake Tahoe, California on Monday, February 19, 2024.

By the time previous storms reached the Sierra, they were much weaker, limiting snowfall at the highest elevations. While California's coastal areas generally received higher than normal precipitation this winter, Tahoe City is 5.4 inches behind normal winter precipitation. Bare pavement was a common sight around Lake Tahoe until late January.

Strong wind

The strong jet stream will help push the Arctic low pressure system deeper than previous seasonal storms. Wind speeds in the upper atmosphere can exceed 150 mph, and winds at the top of the Sierra are expected to reach 110 mph.

Winds exceeding 150 mph in the jet stream, located at about 30,000 feet, will push a powerful winter storm toward California this weekend.

Winds exceeding 150 mph in the jet stream, located at about 30,000 feet, will push a powerful winter storm toward California this weekend.

Baron/Lynx

When the jet stream encounters the steep terrain of the Sierra Nevada, the storm's frigid air has nowhere to go but up. Mountains squeeze moisture from the atmosphere, turning water vapor from a gas into ice. When snowflakes become heavy enough, they fall from the sky.

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This process, or orographic uplift, is why the westward-facing slopes of the Sierra Nevada receive more precipitation than the eastern summit.

Due to the unusually cold nature of the storm, even lower elevations in the Sierra Nevada could benefit from a mountain lift, in the form of snow instead of rain. Hills communities like Grass Valley could pick up a few inches to a foot of snow. In the Bay Area, several inches of snow are expected in Lake and Mendocino counties up to 1,000 feet, and a half-foot or more of snow is likely on Mount Hamilton and Mount Diablo.

Big snow

As the jet stream changes, the Sierra Nevada will be ideally positioned to receive heavy rainfall, with expected amounts rivaling long-standing records.

This map shows three-day snowfall records for every county in California. The record in Tahoe City was 9.75 feet, set in 1911.

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Cold storms produce more snowfall per inch of water than their warmer counterparts. The typical ratio is 10 inches of snowfall to one inch of water, but with this storm the ratio could be 15 to 1; “It can be as much as 18 or 20 to 1 sometimes,” Schwartz said. “So, there's light, fluffy snow, which is something we don't get a lot of here.”

In contrast, storms earlier this winter brought heavy, wet “Sierra cement” with low snow levels.

Snow is measured twice a day in the lab, at 8 a.m. and 4 p.m., but with 7 to 9 feet of snow expected, Schwartz will not only be measuring powder this weekend, he'll be making his way out of it — nonstop.

“It's survival mode,” Schwartz said.

Contact Anthony Edwards: Anthony.Edwards@sfchronicle.com Contact Jack Lee: jack.lee@sfchronicle.com

(tags for translation) Blizzard

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