The previous wettest May was in 1957 with 4.24 inches of precipitation, and the previous wettest month was October 2009 with 4.29 inches of precipitation.That one number representing the average precipitation across the lower 48 states is calculated using climate division data in each state. An average for each climate division is determined from the precipitation observations mapped to a 5 kilometer grid.
It's interesting to note that the May 1957 precipitation departures were also highest in the southern and central Plains, but also extended west to California. In all three cases the percent of the U.S. that was classified as very wet (in the top ten percent of the historical distribution) was 43 to almost 45 percent.
|Percent of mean precipitation for May 1957 which is now the second wettest May on record.|
|Percent of mean precipitation for October 2009, now the second wettest month on record.|
The fact this was a record wet May is not surprising news for those living in the southern and central Plains. It was the heavy precipitation over a rather large area that contributed to the record total. It was the wettest month ever in Texas and Oklahoma, and Colorado recorded its wettest May on record. It was the second wettest May in Arkansas, Kansas, and Utah.