Comparing May 1993 and 2019 Palmer Drought Severity Index
Summer 1993 Was Super Wet; Summer 2019 Not Quite As Wet
Discussion: More moderate to heavy rainfall is forecast for the Corn Belt this weekend. This is not the last of it as summer 2019 promises to be wetter than normal for this region. The last wet summer on top of prohibitive wet soils as springtime ended was in 1993 (Fig. 1). The core of the wettest soils in May 1993 was Kansas and Oklahoma. Slightly more intense Palmer Drought Severity Index (PDSI) is present this year in the Great Plains strongest in Nebraska (Fig. 2).
The 6-month precipitation pattern across the U.S. leading to the soaking wet May 1993 PDSI signature was an El Nino inspired very wet regime from the Southwest U.S. to the Great Plains (Fig. 3). In 2018-19 the wet pattern was inspired in-part by weak El Nino and an active Madden Julian oscillation (MJO). The wettest weather has been across the Mid-South U.S. (Fig. 4).
During summer 1993 the warming atmosphere across the flooded Great Plains lead to more excessive rainfall centered on Iowa (Fig. 5). The summer 2019 forecast by Climate Impact Company indicates another wet summer ahead although not as excessive as 1993 (Fig. 6).
Fig. 1-2: The Palmer Drought Severity Index for May 1993 versus May 2019.
Fig. 3-4: The 6-month (DEC-MAY) precipitation anomalies for 1992-93 and 2018-19 (leading to historic wet soils).
Fig. 5-6: The summer 1993 observed rainfall anomalies and Climate Impact Company summer 2019 forecast rainfall anomalies.