By Jack Lee, San Francisco Chronicle The Tribune Content Agency
The snowiest place in California is not at a ski resort in Lake Tahoe. And it's not close to Mount Whitney in the Sierra Nevada, the highest point in the contiguous United States.
According to a Chronicle analysis of snowfall data over the past 16 seasons, it's actually located just south of Lassen Peak in Shasta County, around Bumpass Mountain. An average of about 45 feet of snow falls there each year. No other area is even close. Only other locations near Lassen Peak reach over 40 feet.
The map below shows average annual snowfall across California, down to a resolution of about 2 miles. The area around Lassen Peak stands out in dark blue on the map - darker hues indicate more snow. Areas in gray reflect places that typically don't get snow.
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The data shows that the snowiest region south of Sacramento is near Dorothy Lake, straddling Mono and Tuolumne counties, with 39 feet of snow per year on average. The snowiest place in Southern California is in San Bernardino National Forest, around Poopout Hill, with just under 9 feet.
The snowfall statistics come from the National Weather Service's National Gridded Snowfall Analysis tool. This tool calculates snowfall across the contiguous U.S., offering a level of geographic detail that can't be obtained from the hundred or so snow stations located in California.
The estimates are based on calculations involving direct observations, National Weather Service precipitation estimates, climatological snow-to-liquid ratios and forecast models.
How California mountains affect snow
The combination of Lassen Peak's elevation and geographic orientation contribute to the area's high snow numbers, explained Katrina Hand, a meteorologist with the National Weather Service's Sacramento office.
Places at high elevation in California often receive extra precipitation because the mountains force air to rise. As air cools, moisture is squeezed out in the form of rain and, if it's cold enough, snow.
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Lassen Peak also faces storms fueled by atmospheric rivers, streams of water vapor in the sky. These storms can dump large amounts of rain and snow on California. A gap in the coastal mountains at San Francisco Bay can allow large amounts of moisture to flow inland during an atmospheric river, said Michael Anderson, state climatologist with the California Department of Water Resources, by email. This moisture can, in turn, fuel storms that end up hitting Lassen Peak.
Winds blowing parallel to the Sierra can provide an added boost. These winds are not always present, said Anderson, but when they are present, they provide additional lift to storms going into the Lassen region.
Mount Shasta, to the northwest of Lassen Peak in Siskiyou County, averages less snow per year at around 31 feet. That's despite the mountain rising to over 14,000 feet, which is notably higher than Lassen Peak's elevation of 10,457 feet.
Topography could be one reason. California storms generally travel from west-to-east from the Pacific. For the Sierra Nevada and Lassen Peak, in the Cascade Range, that means storms traverse the relatively flat Central Valley before slamming into mountains.
By contrast, other mountains come between the Pacific Ocean and Mount Shasta. That could mean moisture is squeezed out of storms before they even make it to the towering peak.
This topography is why the weather systems that generally produce more snow on Mount Shasta come from the south, said Tim Daldrup, a meteorologist with the weather service's Medford, Oregon office.
"You get upslope in that area and that's what kind of wrings out all the moisture from the air," Daldrup said. "And it comes down in snow when it's cold enough."
A bomb cyclone that was just offshore of California in November brought such southerly flow, resulting in feet of snow in the area, causing Interstate 5 to shut down near the California-Oregon border.
Reach Jack Lee: [email protected]