(CNN) — A major change in weather patterns will produce the first atmospheric river of the season in…
(CNN) — A major change in weather patterns will produce the first atmospheric river of the season in California next week. Significant rain and snowfall are forecast in the state, while wet and gloomy days are ahead elsewhere in the western United States, as signs of El Niño’s influence on the upcoming winter season emerge.
November began with rain in the Pacific Northwest, but it did not reach Southern California. Two scenarios will dramatically change that trend next week: A southward dip in the jet stream – the fast-moving river of air that carries storms around the planet – will be aimed directly at California; and a large area of disruptive atmospheric energy will remain just off the west coast.
Next week’s storms will be fueled in part by an atmospheric river, the region’s signature type of winter storm, which transports abundant moisture from the tropical Pacific directly to the West Coast.
During the winter of last year, the West was drenched by many of these systems: California alone saw at least a dozen major atmospheric rivers, leaving at least 18 people dead and extensive damage to infrastructure. But they also brought rain and snow to a region that desperately needed them, filling reservoirs and allowing water managers to stock up and prepare for a future with less fresh water.
Atmospheric rivers are rated on a five-point scale, where 1 describes “weak” storms and 5 is classified as “exceptional.” Next week’s phenomenon is expected to be at least level 2 out of 5, that is, a “moderate” atmospheric river.
Rain will arrive in Northern California starting Monday and spread to parts of Central California on Tuesday. Rainfall in Southern California will largely depend on the exact evolution of the storm early next week, but wet weather is likely to begin late Wednesday or Thursday.
Once the rain begins, it will continue at varying intensity for much of the week and into the weekend in some areas. Rainfall amounts are not expected to reach catastrophic levels that would cause widespread flooding, but many locations could receive more than a month’s worth of rainfall in a matter of days.
Any amount of rain will be important. California hasn’t had several days of rain since the summer, and many places are in a rainfall deficit compared to average.
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Between September 1 and November 9, San Francisco and Los Angeles have only recorded 6% of the average rainfall for the period. Despite this precipitation deficit, California is drought-free for the first time in nearly four years: The state reported no areas of drought in mid-October, which was the first such reading since January 2020.
Rain isn’t the only concern next week: The storm setup is set to bring significant snow to the Sierra Nevada mountain range.
Several centimeters of snow could fall in the higher elevations of the Sierra, with up to 30 centimeters in some foothills by next weekend. The elevation where rain will turn to snow will start fairly high next week, but snow will likely begin to accumulate in the lower elevations of the mountains by the end of the week as colder air creeps through the region.
Elsewhere in the west, there will be no discernible break in the monotony with the new influx of wet weather next week, and the northwest will remain wet both this weekend and next week.
El Niño and atmospheric rivers are related
Like many other elements of the upcoming winter – including temperature and snow – studies have shown that El Niño influences the behavior of atmospheric rivers.
A 2017 study found that atmospheric rivers are more 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, but its strength can also affect how often it occurs. According to a study published in January, the frequency of atmospheric rivers increases during strong El Niño years, the level expected this winter.
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. (Credit: Justin Sullivan/Getty Images)
Like any meteorological phenomenon, atmospheric rivers do not depend on a single variable. Thus, the presence of a strong El Niño phenomenon does not necessarily guarantee a greater frequency of atmospheric rivers.
For example, the 2017 study also found that atmospheric rivers are less likely to affect the western United States during La Niña. But La Niña was firmly entrenched last winter, when California was hit by a dozen powerful storms.
The-CNN-Wire
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2023-11-13 01:52:40
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