California and the West Coast remain entrenched in a crippling drought that’s left some reservoirs dry and vegetation desiccated, but the atmosphere will deliver another welcome dose of water this week. A soaking slug of heavy rain and feet of mountain snow will plaster the Western U.S., with up to 10 feet of accumulation and blizzard conditions in the mountains amid a replenishing of the Sierra Nevada’s snowpack. The storm could bring issues for holiday travelers, however.
Winter storm watches span the length of the Sierra Nevada, where hurricane-force winds will also combine with the snow to bring near-zero visibilities. In the Cascades, winter storm warnings have been issued. Freezing fog was already affecting parts of Northern California and the Great Basin of Nevada early Monday, an undesirable prelude to an extended period of inclement weather.
The National Weather Service is warning of “major travel disruptions” likely in the West, writing that Monday was “the last ‘all clear’ weather travel day.” AAA is estimating that more than 109 million Americans will travel 50 miles or more between Dec. 23 and Jan. 2, a spike of 27.7% over last year.
“The duration and the amounts do look pretty impressive,” said Dan Harty, a meteorologist at the National Weather Service in Hanford, which serves California’s San Joaquin Valley. “It’ll be pretty high snow levels initially, about 7,000 feet, so it’ll be Friday or the weekend before we get lower snow levels. But we’re looking at feet of snow Wednesday into the weekend.”
Instigating the snows is a pocket of cold air and low pressure positioned well to the northwest, whose counterclockwise swirl is tugging ashore a filament of moisture-rich air. That ribbon of juiced-up atmosphere, known as an “atmospheric river,” will be forced up the mountains into chilly air aloft, transforming that moisture to snow.
The atmospheric river won’t be overly intense. In fact, it’s a meager one — only a level 2 out of 5 on the Center for Western Weather and Water Extreme’s ranking scale. While vapor transport won’t be intense, the longevity of the system is noteworthy. A moist flow will remain pointed at Washington and Oregon through early Wednesday, with central California in the crosshairs of that stream between Tuesday night and late Thursday. Midlevel temperatures will also cool about 15 degrees during that interim, allowing snow to expand to lower elevations.
“Holiday travel’s going to be a big concern given the time of year,” Harty said. “The passes farther north, you go up to I-80, there could be big problems. Interstate 5 over the Grapevine should be rain through the week but could switch to snow by Friday.” Snow levels by then could locally dip to around 2,500 feet.
All told, totals of 5 to 10 feet are possible in the Sierra Nevada, the heaviest of which will come down Thursday. Snowfall rates may exceed half a foot per hour. The Coastal Range in northern California could see a couple feet of snow too. Oregon and Washington will see their mountain snows Thursday as well before a resurgence of additional snow with the next system Saturday.
“Major travel delays and difficult travel conditions are anticipated,” wrote the National Weather Service in Sacramento. “Gusty winds will further reduce visibilities during this event with local whiteout conditions possible. Holiday travelers should prepare for winter driving conditions by packing chains, warm winter clothes, and extra food and water.”
In the lowlands of Oregon and Washington, where a relentless barrage of atmospheric rivers has brought flooding and extreme rains over the past two months, additional heavy rain is expected. An inch or two is probable along the coast, with lesser totals in the valleys of California; atmospheric rivers carry the bulk of their moisture at the mid-levels, favoring mountains.
While the snow will prove a headache for some, it’s a welcome source of aid in somewhat mollifying the ongoing drought. A year ago, only 1% of California was gripped in a level 4 out of 4 top tier “exceptional drought.” Now 28% of the Golden State, equating to roughly 30 million acres, is included in that high-end category according to the U.S. Drought Monitor. It states that “water shortages are widespread, surface water is depleted, federal irrigation water deliveries are extremely low, junior water rights are curtailed [and] water prices are extremely high.”
Mountain snows are more useful in alleviating drought than rains due to snow’s propensity to last longer.
“The snow melts and the runoff from the snowmelt is what a lot of reservoirs feed off going into the dry season for us,” said Sierra Littlefield, a meteorologist at the Weather Service in Sacramento. “Most of the precipitation that is beneficial for the water sources that’s useful to us in California comes during the rainy season. Typically by April first we see our deepest snowpack.”
Thus far, central California has seen an approximately average amount of snow to date for the season, but with up to 130 inches expected to fall through Christmas, the state may lurch ahead of their end-of-year benchmark. While it’s not nearly enough to eliminate a deficit that’s been growing and wreaking havoc for years, it’s a step in the right direction.
“Adding any more is going to be really good for us in California,” Littlefield said.