U.S. Soil Moisture Key To Summer Heat Risk

Global Soil Moisture Observations and 3-Month Trend
05/08/2018, 6:57 am EST
U.S. Corn Belt Severe Thunderstorm Pattern Ahead
05/11/2018, 8:54 am EST
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Summary: Paramount to anomalous heat risk for the upcoming summer season in the U.S. is LARGE REGIONS of DRY SOILS and their typical hot bias on climate. Conversely, large areas of wet soils typically foreshadow suppressed heat risk. Currently, the southwest quarter of the U.S. is in drought from California to Kansas to Texas. Dryness also prevails across the northern Plains. The far Southeast U.S. is drier than normal. Wet soils dominate the Mid-South, Ohio Valley and Great Lakes region. The northern Rockies are also wetter than normal

The U.S. seasonal soil moisture change has produced drier conditions across the central and southern Great Plains and also drier conditions over northern Minnesota (Fig. 1). The patchy wet changes in the East-Central U.S. are the result of mostly recent rains (Fig. 2). The seasonal change reflects wetter soils in Central California reversing drier in May. The East/Southeast U.S. has been generally drier this spring season except recent buoyant rainfall in the Carolinas.

The 15-day outlook according to the GFS ENS indicates the percent of normal precipitation is higher than normal across the U.S. Corn Belt and into the Mid-Atlantic region due to frequent thunderstorms (Fig. 3). The Southeast U.S. and particularly Florida is very wet due to a subtropical rainfall induced by the Madden Julian oscillation (MJO). The Interior Northwest also turns showery. The Southwest and Texas are dry where drought intensifies the second half of May.

Fig. 1: Seasonal soil moisture change across the U.S.

Fig. 2: May soil moisture change so far across the U.S.

Fig. 3: U.S. percent of normal rainfall for the next 15 days forecast by the GFS ENS.

Summary: The U.S. soil moisture profile on June 1 emerges as a lead climate predictor of heat risk to the U.S. for the summer season. The Southwest and Texas are in drought and run a high risk of an unusually hot summer especially in the Southwest where early season heat episodes are already established. The dryness in the Southeast and Florida could be eased by the MJO-induced heavy rains forecast during the medium-range lowering anomalous heat risk for summertime in that zone. The Mid-South to East-Central U.S. are wet and stay that way into early summer indicating a zone of suppressed heat risk for summertime ahead.