Hemispheric composites of 700 mb height during each of four unusually warm summers in the contiguous United States show a characteristic “3-wave” pattern of anticyclonic anomalies over the eastern North Pacific, the United States and the North Atlantic. Other common features are an anticyclonic anomaly over eastern Russia and mostly above-normal heights for the entire Northern Hemisphere north of 15°N, especially over subtropical and lower middle latitudes. For tour unusually cool summers, generally inverse composite patterns are noted. Sea level pressure composites for those warm and cool summers show similar, but less well defined, anomalies.
More generally, based on 33 years of data and Monte Carlo testing procedures, there appears to be a statistically significant lagged relation between zonally averaged 700 mb height anomalies at lower latitudes of the Northern Hemisphere and subsequent mean summer temperatures in the United States. Relations from sector-averaged anomalies are mostly inferior to those from hemispheric zonal averages. Correlations of lesser significance exist between zonally averaged 700 mb height anomalies at middle and high latitudes and subsequent mean summer temperatures.