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

Abstract

This paper deals primarily with the 1988 summer drought over much of the contiguous United States and its generation from conditions during the preceding spring. Both the spring and summer environment are described in terms of hemispheric flow patterns in midtroposphere, temperature and precipitation anomalies, and sea surface temperature anomalies. Conditions in March were especially indicative of the ensuing drought, since a model routinely employed in long-range forecasting showed that the March circulation would most likely be followed by a hot dry April, May, and June over much of the nation?a pattern which persisted into early summer. This result suggests that the initiation of the drought was rooted in extratropical climate variations, an alternative hypothesis to one which attributes the persistent drought-producing circulation to oceanic and atmospheric conditions in the tropics. In many respects the summer drought of 1988 was similar to earlier great droughts of the Great Plains, although it was spatially more extensive. Attempts by three forecast groups to predict the summer conditions from spring's were moderately successful, though none of these anticipated the drought's severity and extent. The underlying reasons for the summer forecast made by the author are verified using objective tools. Premonitory signs showed up in antecedent seasons when deficient precipitation occurred, when climatological contingencies provided alerts, and when extratropical sea surface temperature patterns evolved in a conducive manner. A new modified barotropic model iterating from the May midtropospheric height pattern using a mean summer estimate of seasonal forcing produces a reasonably successful estimate of the summer circulation and, in retrospect, even more so when initialized from the March height pattern for the April, May, and June period of inception.