Gary McManus, Associate State Climatologist; Oklahoma Climatological Survey
The recent cool weather and smattering of rain enjoyed by Oklahoma came too late to forestall the impacts from over a month of extreme temperatures and dryness. The latest depiction from the U.S. Drought Monitor indicates moderate drought has now gained a foothold in the southeastern one-half of the state.
While that is the mildest intensity of drought the Drought Monitor reports, it is often the precursor to more severe development.
The Drought Monitor authors solicit advice from local experts at the Oklahoma Climatological Survey and National Weather Service to determine Oklahoma’s drought picture.
The short time it took for the current drought to develop is indicative of a “flash drought” episode. A flash drought can occur when abnormally dry and hot weather negatively affects vegetation and water supplies.
Oklahoma was in relatively decent shape going into the hottest and driest part of summer with abundant moisture from June to mid-July. Statewide average rainfall statistics from the Oklahoma Mesonet indicate the June 1-July 12 period was the 13th wettest on record for Oklahoma with a surplus of 2.31 inches. Southwest Oklahoma experienced its wettest such period on record with a surplus of over 4.30 inches. Mother Nature turned the spigots off shortly thereafter, however, and the temperatures began to soar.
Much of the southern one-half of the state received 20-40 percent of normal rainfall since July 12. More than 20 Oklahoma Mesonet stations in southwest, central and east central Oklahoma have recorded less than an inch of rainfall during that period. Oklahoma City has been particularly dry with a meager 0.09 inches of rainfall. Combine that dryness with 14 days of high temperatures at or above 100 degrees and the prime ingredients for a flash drought are in place.
The cooler weather the state has seen over the last few days will help ease the progression of the flash drought, but precipitation is now needed to ease the dryness already in place. The state’s secondary rainy season of September and early October is quickly approaching so perhaps some much-needed moisture recharge is in store. Farther out, La Niña conditions currently developing in the equatorial Pacific could mean a warmer, drier winter for the state so a fall recharge could become even more important.