Skewness analyses of cumulative rainfall and mean temperature for July-August-September periods during which eastern Pacific SST anomalies were above the highest (warmest) sextile of the period 1895-1997. Shaded climate divisions indicate areas that experienced a significant incidence of above or below median seasonal climate. Confidence levels for skewness can be found under the Above Median colorscale legend. Where climate divisions are annotated, significant skewness in the highest or lowest 25% of the historical distribution was found, with (n/m) indicating n seasons in the first 25%, m seasons in the fourth 25%.

      A significant tendency to above median rainfall and below median temperature over portions of the lower Missouri River drainage region is evident. This cool-wet climate signal also extends into climate divisions of Montana and Northern Wyoming analyzed but not shown. Carlson et al. (1996) also note a tendency to cool and wet conditions over Iowa during El Niño summers, and results found here suggest the wider extent of this signal. However, while the climate shift they noted was relative to La Niña conditions, the shifts indicated here are relative to climatology. Evidence of significant fourth quartile seasonal rainfall is also apparent in corn belt climate divisions in eastern Nebraska, Iowa, and northern Illinois.