WASHINGTON — Last month was the wettest on record for the contiguous United States, according to federal meteorologists.

On average 4.36 inches of rain and snow – mostly rain – fell over the Lower 48 in May, sloshing past October 2009 which had been the wettest month in U.S. records with 4.29 inches. National Oceanic and Atmospheric Administration records go back to 1895.

NOAA climate scientist Jake Crouch calculated that comes to more than 200 trillion gallons of water in May.

Crouch said the record was triggered by a stalled pattern of storms that dumped massive amounts of rain in the central U.S., especially in Texas and Oklahoma, which had their rainiest months.

Oklahoma and Texas had been in a five-year drought and it was washed away in just one month, Crouch said: “It’s like one disaster ending a catastrophe.”

Colorado had its rainiest May on record. Arkansas, Nebraska and Utah had their second wettest month on record. Fourteen states had one of their 10 rainiest Mays on record, all of them west of the Mississippi River and east of California.

Still, parts of the Northeast were unusually dry. It was the second driest May for Massachusetts and the third driest May for Rhode Island and New Jersey.

In Maine, a total of 2.07 inches of rain fell during the month, nearly 2 inches below normal, at the National Weather Service office in Gray. The record for May rainfall is 8.54 inches, set in 2006.

Last month was 1.45 inches wetter than 20th-century average for May. It was only the seventh time the entire contiguous United States averaged four inches of rain or more.

The global climate phenomenon El Nino, which starts with a warming in the central Pacific and changes weather worldwide for a year or so, is usually associated with such heavy rainfall, Crouch said. He added that it is too early to say if it triggered the record moisture. Also, more heavy downpours are expected as the world warms, but Crouch said there’s no way to connect climate change to a single, soggy month.

May’s average temperature in the U.S. was 60.8 degrees, which is slightly warmer than the 20th-century average. However, Connecticut, Massachusetts, New Hampshire and Rhode Island had their warmest Mays on record.

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