The Record-breaking Extreme Hot/Dry Summer of 2011 in the Southern Plains: Indications from Teleconnection Patterns
With the best single factor, the summer temperature and precipitation variations can only be accounted for 13% by North Atlantic Oscillation (NAO) and 6.5% by Pacific North America (PNA) pattern, respectively. Multivariate regression models based on the search for optimal number of predictors and the best subset of predictors were able to explain much more variations in the predictands. With assurance from cross-validation, the best models can explain 42% and 24% of variations in the target study area's temperature and precipitation, respectively.
Supplemental synoptic analysis of the 500 hPa geopotential height anomalies from multiple extreme hot/dry and cold/wet summers, in addition to 2011, helps confirm that teleconnection patterns did affect and contribute to the heat and drought in the summer 2011. The most obvious features concluded from composite geopotential height fields are related to Arctic Oscillation (AO), NAO, and PNA patterns. To the regional climate in the central United States, the anomalous high ridge at upper levels maintained in the area caused more clear skies and less cloud cover, which leads to hot and dry summers. The cold/wet summers are results from an opposite synoptic situation.
Overall, the statistical analysis captures well the climate variations that are near normal. The synoptic analysis helps explain further the variation in extreme conditions. Yet, other longer-range variations and local climatic processes may help to fully explain the record-breaking extreme event.