By AccuWeather meteorologist
Published Dec. 8, 2022 6:04 AM AKST | Updated Dec. 9, 2022 3:32 PM AKST
A strengthening and growing storm over the Pacific will overspread much of the West Coast before turning inland this weekend with adverse conditions ranging from heavy rain to feet of snow over the mountains, AccuWeather meteorologists say. The same storm will set the stage for severe weather and blizzard conditions in the nation’s midsection next week.
The storm will continue to help grow the snowpack throughout the West and deliver much-needed rainfall as far south as Southern California.
A smaller, weaker lead storm produced rain and high-elevation snow on Thursday and Thursday night in Washington, Oregon and Northern California, forecasters said.
The remnants of the storm were still producing spotty snow over the northern Sierra Nevada and areas hundreds of miles farther to the east in Idaho and northern Utah on Friday.
But already on Friday afternoon the leading edge of the next storm's rain and mountain snow was falling on areas from western Washington to Northern California.
While a few inches of rain will fall in some areas along the coast, prompting wet roads and localized ponding, the snow will be the most noteworthy aspect.
"A strong Pacific storm will bring multiple feet of snow once again to the Sierra Nevada, where the seasonable average snowpack is up to 175% of normal in parts of the area," noted AccuWeather Meteorologist Mike Youman.
The substantial amount of snow piling up in the mountains is crucial. Experts say that a greater snowpack means there will be more snow to melt away in the drier months of the spring and summer. The snowmelt can help boost soil conditions as well as water levels on streams, rivers and water reservoirs.
Frequent storms over the past month have helped grow the snowpack substantially in the Sierra Nevada.
Any precipitation is welcome in California where a moderate to exceptional drought is still ongoing according to the United States Drought Monitor. The Sierra Nevada has peaks above 8,000 feet that tend to screen out a lot of moisture from Pacific storms. However, it looks like a fair amount of low-elevation showers and mountain snow will push eastward into the Colorado River basin, where drought and low water levels are also an ongoing concern, forecasters say.
Despite the long-term benefits, travel over Interstate 80 could be nearly impossible during the height of the storm. Snow-packed and slippery roads will be hazardous, and visibility will be sharply reduced due to the intensity of the snow. Several inches of snow could accumulate in just an hour's time.
Before the storm affects California, rain, snow and wind will crash into the Northwest by Friday night. Precipitation will increase in earnest Saturday in much of northern and central portions of California. The precipitation is likely to continue right through the weekend.
"One to 2 inches of rain look likely across the Bay Area from Saturday afternoon through Sunday night," said Youman. "Amounts at the higher end of that range would get San Francisco within roughly a half-inch of the city's rainfall average for the entire month of December, with two-thirds of the month to go," added Youman.
Soaking rain to reach Southern California
As a large southward dip in the jet stream occurs, Southern California will not avoid the rain from this system. Rainfall will not be as heavy as in the northern parts of the state, but amounts will still be beneficial.
The Los Angeles Basin is expected to receive 0.50 to 1 inch of rain, roughly 50% of Los Angeles's normal December rainfall, according to Youman, who noted that this would fall in a period of only 48 hours.
AccuWeather meteorologists say that a few thunderstorms could develop across Southern California this weekend. Thunderstorms this time of year in the region are not unheard of, but they typically need quite a strong storm system to form for them to occur.
In the San Diego area, steady and potentially heavy rain is expected to move through the city and surrounding areas Saturday night, with showers lingering into Sunday, according to AccuWeather Senior Meteorologist Adam Douty.
"Since the rain can be heavy at times, flooding in low-lying areas will be a concern later Saturday night into Sunday," Douty said.
The last soaking rain in the city occurred back on Nov. 7-8 when 0.94 of an inch fell. Rain amounts in San Diego with this upcoming storm are expected to range from 0.50 of an inch to 1 inch through the event. The normal rainfall total for the month of December in the city is 1.67 inches.
The weather along the West Coast should begin to quiet down Monday as snow moves into the Rockies. The system is then expected to rapidly intensify and become a monstrous storm in the central United States by Tuesday.
In the wake of the storm, windy and much colder conditions will settle over the West, particularly in the Southwest. Temperature departures from average will range from 10 to 30 below normal for the middle of December. In Los Angles, highs will be in the low to mid-50s, compared to a normal high in the upper 60s.
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