The Mid-summer 2012 Flash Drought in the Central Great Plains
Fig. 1-2: U.S. state rankings for precipitation and temperature during July 2012.
Fig. 3-4: Deep layer (10-200 CM) soil moisture deficits for June 30/July 1, 2012 and the July 2012 500 MB anomaly analysis.
Discussion: The flash drought/excessive heat regime observed in July 2012 was centered on the central Great Plains (Fig. 1) with attendant heat spread across most of the U.S. (Fig. 2). Nebraska, Iowa and Illinois observed all-time top-5 driest mid-summer months on record. The drought condition came on fast most likely due to developing high-pressure aloft across a vast area of deep layer soil moisture deficit (Fig. 3).
During July a feedback loop developed as the combination of deep layer soil moisture deficits caused by long-term rainfall shortages combined with anomalous heat rapidly caused shallow layer (0-10 CM) soil moisture deficit to accelerate, i.e. “flash drought”. The expanding and intensifying region of soil moisture deficit combined with evolving anomalous heat warmed the atmosphere amplifying the upper-level high pressure ridge (Fig. 4) which in-turn caused further acceleration of surface heating and soil moisture loss.
During early spring in 2012 a large region of deep layer soil moisture deficit was present across the Interior West and into the western Great Plains and given the required weather pattern to follow indicated potential for a summertime flash drought was certainly evident (Fig. 5). As of mid-March 2021, a vast area of soil moisture deficit in the deeper layer is not present (Fig. 6) therefore flash drought development for summer 2021 is not evident (yet).
Fig. 5-6: The early spring soil moisture deficit April 1, 2012 and current soil moisture surplus.