April showers, as the saying goes, bring May flowers. Apparently, though, in Earth's new climate regime there is a corallary to this, which goes something like, "May downpours bring deadly floods and all-time rainfall records." At least that was the case this year.

According to data released Monday by the National Oceanic and Atmospheric Administration, May was the wettest month on record in the contiguous U.S. NOAA says the average May precipitation total for the lower 48 states was 4.36 inches, which was 1.45 inches above average.

This was the wettest May on record, and the wettest month of any month since instrument record-keeping began in 1895. So much rain fell that if converted into gallons it would amount to more than 200 trillion gallons of water, according to the AP.

Average May precipitation for the lower 48 states, showing that 2015 edged out previous records.

See also: All the rainfall records that have been broken in the southern Plains so far

For the spring season, the contiguous U.S. precipitation total was 9.33 inches, 1.39 inches above average, and the 11th wettest on record.

May rainfall in Oklahoma City, showing the 2015 record designated by a blue arrow and oval. Image: NOAA/NCEI

Two states — Oklahoma and Texas — blew away their longstanding records for the wettest month, as flooding inundated areas from Lubbock to Oklahoma City, killing about three dozen people. Colorado also saw its wettest May on record.

May precipitation shown as a percentage of average for the month. Image: NOAA

Texas state climatologist John Nielsen-Gammon, who is a researcher at Texas A&M University, has said that such an extremely wet month might have a recurrence period of about every 2,000 years, assuming the climate was stationary (which it isn't, given global warming).

Some of the locations that saw their wettest month on record in May included Colorado Springs, Colorado, Oklahoma City, Wichita Falls, Texas, and Childress, Texas.

Here is how May 2015 stands out in the historical record of Texas and Oklahoma, when plotted on a graph:

May rainfall across the state of Texas, showing the 2015 record designated with a blue arrow. Image: NOAA/NCEI

Oklahoma statewide monthly rainfall for May 2015, showing the record rains this year, but also the prior drought (also circled in blue). Image: NOAA/NCEI

Climate science studies have shown that extreme precipitation events, such as what Texas, Oklahoma and parts of adjacent states saw in May, are becoming more likely to occur due to a warmer, more moist atmosphere.

Paradoxically, so too are extremes in the other direction, and May featured that too as the California drought continued, while drought conditions crept into the Northeast U.S. as well.

The heavy rains erased the longstanding Southern Plains drought, leading to the smallest drought footprint in the lower 48 states since February 2011, a NOAA report said. In fact, parts of Oklahoma went from "exceptional" drought conditions, which is the worst on the Drought Monitor's scale, to no drought at all in just a four week timespan.