Fading La Niña May Queue Up Enhanced Severe Weather Risk for Southern Plains

Even as La Niña begins moving out of the picture this spring, it could be priming the atmosphere for a pattern that favors U.S. severe weather. A forecast group based at Columbia University has issued an outlook for the period March through May calling for enhanced odds of tornadoes and hail across much of the nation, especially over the Southern Plains.

Produced by Columbia researcher Chiara Lepore, the outlook is based on research showing that the state of the El Niño/Southern Oscillation (ENSO) during winter provides some skill in predicting large-scale severe weather patterns across the U.S. the following spring.

La Niña has prevailed in the tropical Pacific for the second straight winter. This winter’s weak to near-moderate La Niña event was more potent than the marginal La Niña episode of 2016-17. In its latest monthly ENSO update, issued Thursday, NOAA’s Climate Prediction Center calls for the current La Niña event to weaken through the spring. CPC also gives an 80% chance that either El Niño or neutral conditions will be in place by the end of 2018.

In line with previous research, the Columbia team has shown that severe weather is more likely over large parts of the nation after a La Niña winter than after an El Niño winter. Their outlook issued for March-May 2018 is quite similar to the example shown for weak-to-moderate La Niña conditions in a 2017 Geophysical Research Letters paper by Lepore and colleagues Michael Tippett (Columbia) and John Allen (Central Michigan University). Since the state of ENSO for a given winter can often be predicted fairly well by the prior October (as was the case this year), the group’s technique can provide an outlook for the next spring’s severe weather prospects with a few months of lead time.