Another Month, Another Wettest 12-Month Period For Lower 48 In Instrumental Record

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Above: Flood waters surround homes in Fort Smith, Ark., on Wednesday, May 29, 2019. The Arkansas crested more than 2.5 feet above the previous all-time record at Van Buren, Arkansas, across the river from Fort Smith. Image credit: AP Photo/Hannah Grabenstein.

Propelled by a two-week siege of widespread severe weather and heavy rain in late May, the contiguous U.S. has once again broken its record for the wettest year-long span in data going back to 1895. According to the monthly U.S. climate summary released Thursday from the NOAA National Centers for Environmental Information, last month was the second-wettest month in U.S. history, with the nationally averaged total of 4.41” just behind the 4.44” recorded in May 2015. All other months in U.S. precipition annals have been no wetter than 4.24”.

The year to date also ranks as the wettest January-to-May period in U.S. history. The nationally averaged total of 15.71” is well above the previous record of 15.13” from Jan.-May 1983. In fact, the difference of 0.58” is almost twice as big as the difference between any other two Jan.-May periods in the 125-year dataset, when arranged from dryest to wettest.


Figure 1. Precipitation averaged across the continguous U.S. for the period Jan.-May for all years going back to 1895, with 2019 standing head and shoulders above all prior years to date. Image credit: NOAA/NCEI.

Four states—Illinois, Kansas, Nevada and South Dakota—are having their wettest year on record to date through May, as noted by weather.com's Brian Donegan. The sodden May pushed the period June 2018-May 2019 into a clear first place for contiguous U.S. precipitation among all year-long time spans going back to 1895.

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The slow-moving upper low generating the rain in Oklahoma will join forces with the Gulf Coast moisture, leading to a dreary weekend across the South with widespread heavy rain and potential flash flooding.


Figure 2. Projected precipitation for the seven-day period from 8 am EDT Thursday, June 6, 2018, through Thursday, June 13. Image credit: NOAA/NWS/WPC.

NOAA’s latest 8-to-14-day outlook shows wetter-than-average conditions over the bulk of the nation, with only the Pacific Northwest projected to be drier than average. NOAA’s monthly outlook for June, issued on May 16, called for better-than-usual odds of wetter-than-average weather over most of the western and central U.S., with typical odds elsewhere.

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https://www.wunderground.com/cat6/Wettest-12-Months-US-HistoryAgain?cm_ven=cat6-widget