Atmospheric Rivers, Bomb Cyclones, El Niño Fuel Wettest 12 Months on Record in Continental U.S.

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There’s never been a wetter 12 months than the period that recently ended, reported the National Weather Service, which has been keeping such records for 124 years.

Cars drive through a flooded street after a storm dumped heavy rain on Los Angeles on February 2, 2019, (Credit: MARK RALSTON/AFP/Getty Images)
Cars drive through a flooded street after a storm dumped heavy rain on Los Angeles on February 2, 2019, (Credit: MARK RALSTON/AFP/Getty Images)

The continental US is also free of severe to exceptional drought for the first time in the two decades the US Drought Monitor has been in business, officials reported.

It’s all a result of hurricanes, atmospheric rivers and the very wet autumn that unfolded between May 1, 2018, and April 30. The effect fits the broad trend of climate change pushing up US precipitation totals.

The continental United States averaged 6 inches of precipitation above average during the one-year period, with 36.2 inches tallied. That blew away the previous record, set in 2015 and 2016, by almost half an inch.

A map created by NASA shows just how much groundwater there was on May 13, 2019, compared with previous months of May. Areas in blue have more groundwater than previous Mays; places in orange and red have less.

Hurricanes, bomb cyclones and El Niño

Hurricanes Florence and Michael dumped massive amounts of rain last year across the Southeast. Atmospheric rivers, which suck water vapor from the ocean and dump it on land, deluged California with rain and snow, helping to pull the state out of drought. And the El Niño weather pattern — with warming, eastward-moving Pacific waters — contributed to the new benchmark.

Rapidly strengthening storms known as bomb cyclones in the winter and spring across the central US also helped bury the previous record.

The exceptional snowfall and rainfall set the stage for a treacherous snowmelt and spring in the Midwest, where huge swaths remain flooded. Though it’s not counted in the new record, the torrent has continued across the Arkansas River Valley in Kansas and Oklahoma, with rainfall 200% above average between May 1 and 27, according to the Arkansas-Red Basin River Forecast Center.

Climate change has forced precipitation records to topple more frequently.

“Heavy precipitation events in most parts of the United States have increased in both intensity and frequency since 1901,” a report from the US Global Change Research Program found. “The frequency and intensity of heavy precipitation events are projected to continue to increase over the 21st century.”

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