A major change of pattern for the delivery of California’s first aerial river of the season is scheduled for next week. Heavy rain and snow are expected in the Golden State, while wet and dreary days are ahead for other parts of the West with signs of El Niño affecting the upcoming winter season.
November got off to a wet start across the Pacific Northwest, but the wet weather did not reach south into much of California. Two things will radically change this trend next week: The southward direction of the jet stream — the fast-moving river of air that carries storms around the planet — will head straight toward California; There will still be a large area of destructive atmospheric energy off the West Coast.
Next week’s storms will be fed in part by an atmospheric river — the region’s signature type of winter storm, which transports abundant moisture from the tropical Pacific Ocean directly to the West Coast.
The West was inundated by several such systems last winter: California alone experienced at least a dozen major atmospheric rivers, which claimed at least 18 lives and caused massive damage to infrastructure. But it also brought much-needed rain and snow to a region that needed it most, filling reservoirs and allowing water officials to assess the situation and prepare for a future with less fresh water.
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Atmospheric rivers are rated on a five-point scale, with 1 describing storms as “weak” and 5 as “exceptional.” Next week’s event is expected to be at least a Level 2 of 5 – in other words, a “moderate” atmospheric river.
Rain will flow into Northern California early Monday, spreading to parts of Central California on Tuesday. The timing of rainfall in Southern California depends strongly on the exact development of the storm early next week, but wet weather will likely begin late Wednesday or Thursday.
Once rain begins, rainfall of varying intensity will continue throughout most of the week and into the weekend in some areas. Rainfall amounts are not expected to reach catastrophic levels that would lead to widespread flooding, but many locations could receive more than a month’s worth within days.
Any rain that falls will be noticeable, something California has never seen before Several days of rain since summer, and many locations are in – Low rainfall compared to average.
From September 1 to November 9, San Francisco and Los Angeles recorded only about 6% of their average precipitation for the period. Despite this rainfall deficit, California is drought-free for the first time in nearly four years: The state reported no drought areas in mid-October, the first such reading since January 2020.
Rain isn’t the only concern next week – it’s windy The setup is set to deliver large amounts of snow to the Sierra Nevada mountain range.
Several feet of snow could fall at the highest elevations in the Sierra, with up to a foot in some foothills by next weekend. The altitude at which rain will turn to snow The snow will start very high next week, but snow will likely start accumulating at lower mountain elevations in earnest late in the week as cold air pulls through the region.
Elsewhere across the West, there will be no noticeable break in the gloom A new influx of wet weather next week, and the northwest will remain wet This weekend and next week as moisture continues to flow through the area.
El Niño and atmospheric rivers are linked
As with many other elements of the upcoming winter – including temperatures and snow – studies have shown that El Niño affects the behavior of atmospheric rivers.
2017 study The detected atmospheric rivers are most likely to impact the western United States during El Niño, when ocean temperatures in the tropical Pacific are abnormally high.
Not only can El Niño affect where atmospheric rivers dump the most precipitation, its strength can also affect how often it occurs. a A study published in January found that the frequency of atmospheric rivers increased during years of strong El Niño events — a level expected this winter.
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A man walks his dog on a snow-covered street as snow begins to fall during an atmospheric river on March 21, 2023 in South Lake Tahoe, California.
Like any climate phenomenon, atmospheric rivers do not depend on just one variable. Therefore, the presence of a strong El Niño does not necessarily guarantee a higher frequency of atmospheric river events.
For example, a 2017 study also found that atmospheric rivers are less likely to impact the western United States during La Niña. But the La Niña phenomenon was firmly in place last winter when California was hit by dozens of powerful storms.