Spring and Summer 1988 Drought over the Contiguous United States—Causes and Prediction

Abstract

This paper deals primarily with the 1988 summerdrought over much of the contiguous United Statesand its generation from conditions during thepreceding spring. Both the spring and summerenvironment are described in terms of hemisphericflow patterns in midtroposphere, temperature andprecipitation anomalies, and sea surface temperatureanomalies. Conditions in March were especiallyindicative of the ensuing drought, since a modelroutinely employed in long-range forecasting showedthat the March circulation would most likely befollowed by a hot dry April, May, and June over muchof the nation-a pattern which persisted into earlysummer. This result suggests that the initiation ofthe drought was rooted in extratropical climatevariations, an alternative hypothesis to one whichattributes the persistent drought-producingcirculation to oceanic and atmospheric conditions inthe tropics. In many respects the summer drought of1988 was similar to earlier great droughts of theGreat Plains, although it was spatially moreextensive. Attempts by three forecast groups topredict the summer conditions from spring's weremoderately successful, though none of theseanticipated the drought's severity and extent. Theunderlying reasons for the summer forecast made bythe author are verified using objective tools.Premonitory signs showed up in antecedent seasonswhen deficient precipitation occurred, whenclimatological contingencies provided alerts, andwhen extratropical sea surface temperature patternsevolved in a conducive manner. A new modifiedbarotropic model iterating from the Maymidtropospheric height pattern using a mean summerestimate of seasonal forcing produces a reasonablysuccessful estimate of the summer circulation and,in retrospect, even more so when initialized fromthe March height pattern for the April, May, andJune period of inception.