Atmospheric rivers are expected to "flood the West Coast" this winter, just as last year the region faced a series of atmospheric rivers that caused devastating flooding and mudslides, according to AccuWeather's October 14 weather report.
According to the National Oceanic and Atmospheric Administration (NOAA), atmospheric rivers are "long, narrow regions in the atmosphere — like rivers in the sky — that transport much of the water vapor out of the tropics."
Meteorologists predict that the first half of winter will produce atmospheric rivers in the Pacific Northwest and Northern California before storms move inland over the Rocky Mountains. However, a “big change” is expected when 2025 rolls around.
The new weather pattern will create favorable conditions for the storm to move south and impact Central and Southern California, said Paul Pastelok, senior meteorologist and long-range expert for AccuWeather.
Meteorologists predict January will be the wettest month of the year for Los Angeles and San Diego. Other cities across the Southwest will experience wet weather as storms move inland.
AccuWeather predicts storm patterns will shift back to Northern California in February.
Atmospheric rivers were more prevalent in the El Nino climate model last winter. La Nina is forecast to occur this winter, although the climate model is expected to be weak, it could affect weather on the West Coast.
While the La Nina climate pattern is not known for regular atmospheric rivers, a weak La Nina winter in 2022-2023 produced nearly 40 atmospheric rivers across the western United States, AccuWeather said.
Pastelok expects the upcoming winter to be similar to 2022-2023 in terms of atmospheric flows, but the forecast could change if water temperatures in the Pacific Ocean change dramatically. If the warmest waters shift east, California could experience a dry, warm winter similar to the winter of 2013-2014.
Outside of California, AccuWeather predicts the winter will be slightly warmer than normal across much of the rest of the U.S., although the Pacific Northwest and inland states like Idaho, Montana and Wyoming are expected to have cooler than normal winters.
According to American meteorologist Anna Wilson, atmospheric rivers are a global climate phenomenon. They can occur anywhere and often a single stream can span several countries. The frequency of atmospheric rivers by the end of this century is likely to nearly double compared to the present.
The more frequent and larger the atmospheric river, the more likely it is that floods will be more frequent and intense. In East Asia, 90% of floods are caused by atmospheric rivers.
