May 2018 is set to go down in history as the warmest on record in Missouri, and perhaps the nation, said University of Missouri Extension climatologist Pat Guinan.
Every day in May charted above normal in Missouri, Guinan said. Many days registered more than 10 degrees Fahrenheit above normal, with preliminary data indicating an average statewide May temperature of 73 degrees, almost 9 degrees above normal. The 30-year mean temperature for June is 73 degrees.
The 2018 temperatures break a record set in 1962. May’s average temperature this year beat the 1962 record by more than 1 degree, he said. The five warmest Mays in Missouri were in 2018 (73.0), 1962 (71.9), 1896 (70.0), 1987 (69.8) and 2012 (69.5). National Weather Service records date back to 1895.
In its weekly Crop Progress and Condition report on May 29, the U.S. Department of Agriculture reported temperatures the previous week averaged 75.1 degrees, 8.4 degrees above normal.
May’s historic heat follows the second-coldest April on record, which Guinan said is “nothing short of amazing.” Temperatures averaged more than 7 degrees below normal in April. Snow events and subfreezing temperatures were common, he said.
“It was one extreme to the other. It is extremely unusual to have this occurrence,” Guinan said. The last such anomaly was from December 1989 (third coldest) to January 1990 (third warmest).
Not only was it hot, it was generally dry during May in Missouri, especially across the northern half of the state and a few southwestern counties. Preliminary data indicate a statewide May average precipitation of 4 inches, more than an inch below normal. Precipitation averaged 1.06 inches statewide last week, 0.09 below normal, according to USDA, with 33 percent of the subsoil moisture short or very short. Long-term drought conditions still affect portions of northern Missouri where surface water supplies are dwindling and subsoil moisture is depleted.
Guinan said some communities have imposed water restrictions and 12-month precipitation deficits in some locations have exceeded 16 inches. St. Joseph reported 19.28 inches between June 1, 2017, and May 31, 2018; normal is 35.6 inches.
Unless significant precipitation falls soon to recharge surface water supplies and soils, row crop and pasture conditions will continue to deteriorate, Guinan said. The June outlook from the National Weather Service’s Climate Prediction Center indicates an enhanced likelihood for continued above-normal temperatures in Missouri. The precipitation outlook is more uncertain, with equal chances for above-, below- and near-normal precipitation anticipated for most of the state.
June is northern Missouri’s second-wettest month, averaging between 4.5 and 5 inches.
Clark County in northeastern Missouri received the least rainfall in May, according to a Farm Service Agency rain gauge just south of Kahoka, where 0.87 inch was reported. Small pockets of pop-up showers brought little relief to parts of the state. Areas near Nevada, Mo., were an exception, with MU Extension agronomist Pat Miller reporting that 5 inches of rain fell in over Memorial Day weekend.
Extension agronomists in northwestern Missouri reported temperatures above 100 degrees in the previous week, with little relief from cooling rains. It was the first time MU Extension’s Graves-Chapple Research Center in Atchison County had seen triple-digit temperatures, according to extension agronomist Wayne Flanary.