THE 1988 drought in the United States has been widely reported, not least as an indicator of the reality of the "greenhouse effect" - see for example ref. 1. On the other hand, drought is a naturally occurring phenomenon. Here we have studied 30-day forecasts of the atmospheric flow over the United States using a complex numerical weather-prediction model initialized with data from May 1987 and May 1988. In addition, an experiment with 1988 initial conditions and 1987 sea surface temperatures was made. The results indicate that much of the difference between the 1987 and 1988 forecasts was associated with interannual variability in sea surface temperature. These results provide complementary evidence to that in ref. 2, which suggested that the US drought was linked to anomalous oceanic conditions in the tropical Pacific. © 1989 Nature Publishing Group.
