Ocean temperatures may hold key to predicting tornado outbreaks

NOAA | APRIL 18, 2016

Scientists with NOAA and the University of Miami identified how patterns in the spring phases of the El Niño-Southern Oscillation (ENSO), coupled with variability in North Atlantic sea surface temperatures, could help predict U.S. regional tornado outbreaks.

Twin tornadoes spawned from the same supercell in the Great Plains. Image credit: NOAA Legacy Photo; OAR/ERL/Wave Propagation Laboratory (PD)

Researchers investigated the spatial patterns of springtime U.S. regional tornado outbreaks from 1950-2014 and their connection to springtime phases of ENSO.

ENSO, or the El Niño-La Niña cycle, is a natural climate pattern in the Pacific Ocean. During an El Niño event, warm sea surface temperatures spread across the tropics.

In a La Niña year, the opposite happens: Cool sea surface temperatures dominate in the eastern tropical Pacific. These temperature shifts have a ripple effect on large-scale atmospheric processes conducive to tornado outbreaks across the U.S.

The researchers focused on four variations of ENSO events: strong winter events that persist well into spring, and weak events that dissipate soon after their winter peak. They found that weak El Niños led to tornado outbreaks in May throughout the Upper Midwest, while strong El Niños led to outbreaks in February across Central Florida and the Gulf Coast.

In contrast, weak La Niñas led to April outbreaks throughout the South, particularly in Oklahoma and Kansas, while strong La Niñas led to April outbreaks along the Ohio Valley and in the Southeast and Upper Midwest.

The results suggest that each of the four dominant spring ENSO variations is linked to distinct and significant U.S. regional patterns of outbreak probability. The strongest tornado connection was with strong, persistent La Niñas, consistent with the Super Outbreak of 1974 and the record-shattering tornado outbreaks of 2011, both of which occurred during strong La Niñas.

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