Published: April 9,2020
The 40 atmospheric river events from October 2019 through March 2020.
More than three dozen atmospheric rivers made landfall on the West Coast from fall through early spring, but a lack of strong events in California led to the development of drought conditions in parts of the state.
An atmospheric river is a thin, but long plume of moisture in the atmosphere that stretches from the Pacific Ocean tropics or subtropics into higher latitudes. They provide a boost to the rain and snow totals produced by storm systems taking aim at the West Coast, mostly from late fall into early spring. Although these events can bring hazardous impacts, they are also beneficial since they help replenish the water supply in the West.
There were 40 atmospheric river events in the six months from October 2019 through March 2020, from near San Diego to Washington's Olympic Peninsula, according to the Center for Western Weather and Water Extremes (CW3E). Seven of the 40 atmospheric rivers were classified as strong.
In the same period of time a year ago there were 41 atmospheric river events, 11 of which were strong to extreme.
The seven strong atmospheric river events from October 2019 through March 2020.
California had just one strong atmospheric river event this October through March, which helps explain the drier-than-average conditions in parts of the state.
Snowpack was just 64% of average in California's Sierra Nevada as of April 8. That's despite some significant late-season snowfall gains in the first week of this month.
As of April 7, about 68% and 43% of the state was classified as abnormally dry or in moderate drought, respectively, according to the U.S. Drought Monitor. Most of that dryness was in northern and central parts of the state.
That's in contrast to October 2018 through March 2019, which was wetter than average in much of the state. Soaking rain and heavy mountain snow a year ago was fed by more atmospheric rivers making landfall in the state, including seven strong or extreme events.
Washington was impacted by six of the seven atmospheric rivers from October 2019 to March 2020, so precipitation was near or above average in western parts of the state then.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.
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