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U.S. logs wettest 12-month period in over 120 years

As some places see floods, Northwest remains rather dry

By Jason Samenow, The Washington Post
Published: May 9, 2019, 9:41pm

In just over a year’s time, the nation’s rainfall fortunes have shifted suddenly and dramatically. Rainfall famine has turned to rainfall feast.

Thanks to its wettest 12-month period in recorded history, the amount of U.S. real estate covered by drought has plunged to its lowest level in recent decades, the National Oceanic and Atmospheric Administration reported Wednesday. But at the same time, excessive rainfall and flooding plague large areas of the country.

Precipitation over the past year (May 2018 to April) in the United States has been extraordinary. An average of 36.2 inches has fallen over the Lower 48, the first time it has topped 36 inches over a 12-month period in more than 120 years of record-keeping. This amount is more than six inches above average, according to Weather Underground meteorologist Bob Henson, who first reported the record.

Heavy precipitation extremes have been a staple of U.S. climate conditions over the past year: whether Hurricane Florence’s record-setting rain in the Carolinas, the wettest year on record in Washington, D.C., Baltimore and much of the Mid-Atlantic, a sopping wet winter in California, and recent flooding in the central United States.

Local Angle

While the rest of the nation slogged through the wettest 12-month period in recorded history, it was fairly dry here in the Pacific Northwest. Clinton Rockey, a meteorologist with the National Weather Service in Portland, said the metro area received 25.65 inches of rain from May 2018 through April of this year, or 18 percent less than the 31.4-inch average for that period. “We had a rather dry summer here in the Northwest,” Rockey said. “The rains didn’t really pick up until we got into October.” The past 12 months have been much drier than a year with heavy rainfall. For example, from May 1995 through April 1996, 57.48 inches of rain were recorded at the National Weather Service’s Portland office, or 124 percent more than the past 12 months.

Except for the Pacific Northwest and large parts of New Mexico and Colorado, almost the entire contiguous United States has been wetter than normal over the past 12 months.

The record precipitation over the past 12-months fits into a long-term increasing trend, an expectation as climate warming intensifies rainfall. Since the late 1800s, annual precipitation averaged over the Lower 48 states has risen from 29 to 31 inches, Henson noted.

Following the widespread rains, drought affects 2 percent of the country — about the smallest area since the federal government began official monitoring in 2000.

The sudden lack of drought is remarkable considering that in January 2018, nearly 40 percent of the nation suffered from a lack of precipitation. But since then, storm after storm has eaten away at the dry conditions.

Much of drought relief came in a span of three months this winter. As recently as December, over 20 percent of the nation still suffered from a shortage of precipitation. Then, the Lower 48 posted its wettest winter on record, and the territory affected by drought shrank remarkably.

Nowhere have precipitation fortunes changed as quickly or as radically as in California. In December, 75 percent of the state was in drought. That amount sank to zero after a stormy winter. More than 20 atmospheric rivers, streams of moisture from the Pacific, bombarded the state. Plant life exploded, and the state enjoyed a magnificent “super bloom” in the spring.

El Nino, the episodic warming of waters in tropical Pacific Ocean, is certainly a major driver of the rainfall recovery. It tends to pump subtropical moisture toward the West Coast and nudge the prevailing storm track across the southern part of the country. Here

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