Cool weather dominated a good part of May, and possibly robbed Mother Nature of the heat needed for her most exotic springtime menu item; tornadoes. There was still the normal offering of large hail, damaging winds, and flash flooding, but the twister count was below average. The National Weather Service indicated a preliminary total of 13 tornadoes for the month, well below the 1950-2019 average of 24.4, and a relatively minuscule tally compared to last May’s all-time Oklahoma monthly record of 105. The 2020 preliminary total of 33 also falls below the January-May average of 41.
The statewide average precipitation total was 5.04 inches according to the Oklahoma Mesonet, 0.22 inches above normal and ranked as the 50th wettest May since records began in 1895. It was an all too familiar rainfall pattern for Oklahoma, with roughly the southeastern half of the state receiving an abundance of moisture while the northwestern half suffered deficits. Those deficits approached 3 inches in parts of central Oklahoma, and were generally 1-2 inches elsewhere. Surpluses of 2-4 inches were common across the southeast. Stigler was 9.5 inches above normal with a state-leading 15.06 inches, although Valliant was just a hair behind at 15.05 inches. Kenton occupied a familiar spot with the state’s lowest total of 0.48 inches. The northwest versus southeast rain pattern extended from spring back to the beginning of the year. Spring ended as the 24th wettest on record with a statewide average of 13.1 inches, 1.98 inches above normal, yet the Panhandle suffered its 24th driest at 3.31 inches, 2.58 inches below normal. Spring deficits ranged from 2-4 inches across the northwest quarter, but a bit above that in Blaine and Kingfisher counties. Surpluses peaked at 8-12 inches in far eastern Oklahoma. The first five months of the year ended with a surplus of 4.01 inches, the 14th wettest January-May on record at 18.52 inches averaged statewide.
The month both began and ended with summer-like conditions, but sandwiched in between was an extended period of much cooler than normal weather. Temperatures soared into the 80s and 90s the first few days of the month, while the southwest saw triple-digits. The airport at Frederick reached 108 degrees on May 4 to become the highest temperature ever recorded in the state that early in the year, topping Buffalo’s 107 degrees from May 1, 1992. The weather cooled from there until the final week when highs once again reached the 80s and 90s. Overall, the statewide average temperature as measured by the Oklahoma Mesonet was 66.8 degrees, 1.4 degrees below normal to rank as the 35th coolest May on record. The lowest temperature of the month was 31 degrees at Eva on the ninth – the state’s final freeze of the season. Spring finished on the warm side by 0.8 degrees at 60.1 degrees, the 38th warmest on record. The year was still on a warm pace at 52.9 degrees, 1.3 degrees above normal for the 21st warmest January-May in the books.
Drought took a large step forward across western into central Oklahoma, increasing its areal coverage from about 4% at the end of April to more than 14% at the end of May. Drought also increased in severity in the far western Panhandle with most of Cimarron and Texas counties covered by moderate to severe drought by the end of the month. The June temperature and rainfall outlooks from the Climate Prediction Center (CPC) show little hope for substantial drought relief; increased odds of above normal temperatures and below normal precipitation are indicated across all of Oklahoma. Those odds are reflected in CPC’s June drought outlook, with those areas of existing drought in the state expected to persist and intensify. Additional drought development is termed “likely” across much the rest of northern and western Oklahoma.