Winter T&P anomalies vs. La Niña: Fulfilled expectations, or yet another 'quirky’ ENSO event? Klaus Wolter - 16 apr 08 What are typical U.S. Dec-Feb precipitation associations with La Ni ñ a? What happened in Dec-Feb ? Were the anomalies consistent with La Ni ñ a expectations (where these expectations are statistically well-founded)?

U.S. temperature anomalies in La Ni ñ a winters Eight strongest La Ni ñ a cases: out of 344 climate divisions, 214 (or 62%) show composite anomalies in excess of 0.43 standard deviations (33% tails) vs. 9 below Overall, a big shift towards warmth, unadjusted for temperature trends, but most of these are in southeastern U.S. where trends have been ‘small’.

U.S. precipitation anomalies in La Ni ñ a winters Eight strongest La Ni ñ a cases: out of 344 climate divisions, 82 (or 24%) show composite anomalies in excess of 0.43 standard deviations (33% tails) vs. 63 below Overall, the familiar southern dry/northwest & Ohio valley wet scenario that is typical for La Ni ñ a.

U.S. temperature anomalies in DJF Compared to La Ni ñ a composites (below), 118 divisions hit DJF anomalies in the upper tercile (left; out of 214 flagged divisions) - that is 55% instead of 33% - a Heidke Skill score of +33(!). On the expected cold tail (9 possible), 7 hit that tercile, an even better skill score of +67! The unexpected cold from Arizona to Wisconsin was right along the northern warm La Ni ñ a fringe that would be excluded from La Ni ñ a-only warm forecasts.

U.S. precipitation anomalies in DJF Compared to La Ni ñ a composites (below), 56 divisions hit DJF anomalies in the upper tercile (left; out of 82 flagged divisions) - that is 68% instead of 33% - a Heidke Skill score of +52(!). On the expected dry tail (63 possible), 17 hit that tercile, the only negative skill score of -10! The unexpected wetness from Arizona to Wisconsin was again right along the northern dry La Ni ñ a fringe that would be excluded from La Ni ñ a-only dry forecasts.