Oklahoma Climatological Survey: Cold April feels severe weather impacts

Climatological

Cool weather helped keep severe weather at bay in Oklahoma throughout much of April.

A late spring freeze—damaging in its own right—punctuated the scarcity of severe weather during the month’s first three weeks. The cold eventually gave way to an emphatic exclamation point, however, when tornadoes, flooding, high winds, and a hail-borne catastrophe struck during April’s final week. At least four confirmed tornadoes touched on April 28, including an EF-1 twister that struck near Pauls Valley at the stroke of midnight. The tornado damaged homes and outbuildings on at least two farms before dissipating. Two more tornadoes struck near Stilwell around 6 a.m., and another near Crowder later that morning. Heavy rains of 4-6 inches fell over a wide area from south central through east central Oklahoma, prompting flood warnings. Pauls Valley recorded over 6 inches of rain overnight on the 28th that left downtown buildings flooded and stranded motorists requiring water rescues. Despite the early fireworks, the big show came later that night. A large, solitary supercell thunderstorm began dropping quarter-size hail near Gotebo that evening. As the storm approached Grady County, the hail size increased to golf balls until growing to baseballs as it entered the Newcastle and Norman area. The storm laid a footprint of giant hail through Norman from west to east, hammering cars and damaging homes in its path. The destructive force of the hail was enhanced by winds of over 70 mph.

A hard freeze saw temperatures drop into the mid-20s over nearly the entire state April 20-21. This freeze was particularly jarring since some locations had not experienced freezing temperatures since early March. According to preliminary data from the Oklahoma Mesonet, the statewide average temperature finished at 57.2 degrees, 2.1 degrees below normal and ranked as the 22nd coolest April since records began in 1895. The state’s highest temperature was 93 degrees at Beaver and Slapout on April 25. The lowest reading of 21 degrees came on April’s first day at Eva in the central Panhandle. The first four months of 2021 fell on the cool side at 45.8 degrees, 1.6 degrees below normal and ranked as the 45th coolest January-April on record.

Interstate 44 was a curious dividing line between feast or famine rainfall during April. Areas to the southeast saw plenty of beneficial moisture while areas to the northwest went largely without significant rainfall. Totals to the southeast of I-44 ranged from 3-9 inches, with the Mesonet site at Sallisaw leading the state at 10.09 inches. Totals dwindled rapidly to the northwest, generally falling below an inch. The Mesonet site at Eva had the lowest tally at 0.02 inches for the month. Regionally, the Panhandle experienced its second driest April on record with an average of 0.11 inches, 1.55 inches below normal. East central Oklahoma’s total of 7.47 inches was its 11th wettest, 3.24 inches above normal. The year fell on the wet side at 9.82 inches, 0.13 inches above normal and ranked as the 41st wettest January-April on record.

Drought nearly doubled during April according to the U.S. Drought Monitor, with coverage expanding from about 11 percent of Oklahoma at the end of March to 20 percent at the end of April. Much of that increase came across south central Oklahoma, where long-term deficits had been expanding since late fall 2020, and over the western third of Oklahoma with its shorter-term deficits. Longstanding drought in the western Panhandle continued unabated during April. The May temperature outlook from the Climate Prediction Center indicates increased odds for above normal temperatures for all of Oklahoma, but especially the southwestern half of the state. The precipitation outlook sees increased chances of drier than normal weather across far western Oklahoma and the Panhandle, but above normal precipitation in the far southeast. CPC’s May drought outlook sees drought development as “likely” across the western one-third of the state, but drought removal or improvement across south central Oklahoma.