The Two Faces of August
By Gary McManus, Oklahoma Climatological Survey
August 2, 2013
The unusually mild and wet conditions of July continued into August for a couple of weeks, but summer returned with a vengeance to finish out the month. The rains disappeared after week two, and then a summer-like heat wave arrived during the final week. Despite that late heat, the month still managed to finish a tad on the cool side overall. According to preliminary data from the Oklahoma Mesonet, the statewide average temperature was 80.1 degrees. 0.3 degrees below normal and the 49th coolest August since records began in 1895. The abundant rainfall during the first two weeks of the month, mainly across the northern two-thirds of Oklahoma, pushed the statewide average into the surplus territory at 3.04 inches, about a quarter-inch above normal. That ranks the month as the 51st wettest August on record. The southern third of the state missed out on the bountiful moisture and finished from 20-80 percent of normal for the month. Hugo and Newport finished with less than a quarter-inch of rainfall for the month, and many other locations across southern Oklahoma saw less than an inch. The northern two-thirds of the state recorded more generous totals with numerous amounts between 5-7 inches.
The climatological summer (June-August) had two distinct rainy periods that vaulted it up the wet side of the rankings – the first half of June and then mid-July through mid-August. The statewide average for the summer finished at 12.50 inches, 2.73 inches above normal to rank as the 24th wettest on record. Oklahoma City’s official measurement site at Will Rogers recorded 18.15 inches of rain from June through August to finish with its sixth wettest summer season on record. Oklahoma City records date back to 1891. Its January-August total of 45.19 inches ranks as the wettest in the city’s history. In contrast, the Mesonet site at Altus recorded a paltry 4.7 inches of rain during the summer and an equally depressing 11.5 inches for the first nine months of the year. Only the Mesonet stations in the western Panhandle recorded less from January through August.
The return to a more summer-like rainfall pattern the last two weeks of the month put the brakes on any continued drought relief, and actually reversed it across parts of the state. The U.S. Drought Monitor report released on August 28 indicated that 38 percent of the state was suffering from at least moderate drought, up from 33 percent the previous week. Most of that increase came from southern Oklahoma. It is still a vastly different story than one year ago in late August when 100 percent of the state was entrenched in drought, including 90 percent in the extreme to exceptional categories, the two worst possible on the Monitor’s intensity scale. Still, the summer rains allowed for great strides. As much as 59 percent of the state was experiencing drought at the end of May. The Drought Monitor’s worst two categories, severe and exceptional, dropped from 27 percent at the end of May to 10 percent at the end of August.
The September outlooks from the National Weather Service’s Climate Prediction Center (CPC) give equal chances for above-, below- or near-normal temperatures and rainfall for all of Oklahoma. The U.S. Monthly Drought Outlook for September shows drought persisting across all areas of Oklahoma where it currently exists, although no new areas of drought development are expected by CPC. The latest odds continue to favor neutral conditions in the equatorial pacific waters for the second straight cool season, so the development of either El Niño or La Niña appears unlikely at this time. La Niña favors warmer and drier weather during the cool season across the southern third of the United States, including Oklahoma, while El Niño favors wetter and cooler conditions. Neutral conditions tilt the odds more towards normal with perhaps more variability. The La Niña episodes of 2010-11 and 2011-12 helped fuel the dry and warm weather that was so persistent through that period.