Depending on the severity of La Niña, most of Indiana could be in store for a slightly cooler and wetter winter, says Petra Zimmermann, who teaches climatology at Ball State and faculty director of the university’s meteorology and climatology laboratory.
La Niña is defined as cooler than normal sea-surface temperatures in the central and eastern tropical Pacific that impact global weather patterns, she said.
Recent readings of the Southern Oscillation Index (SOI) and Multivariate ENSO Index (MEI) indicate the Pacific Ocean moving into a La Nina event. A La Niña generally sends the polar front jet stream into a wavier pattern, with dips and valleys called ridges and troughs. This affects tracks of storms and whether or not cold Canadian air plunges toward the equator.
“The response in Indiana should be more muted than in some other parts of the nation,” Zimmermann said. “Generally, one can expect slightly cooler and wetter winter conditions, but again, that depends on the severity of the La Nina. Assuming a mild or moderate La Niña, I predict low-to-medium chances of slightly cooler temperatures, particularly for the northern two-thirds of the state. However, given Indiana’s fickle response to La Niña in the past, there’s a reasonable chance that temperatures could be average or even somewhat above average.”
Slightly above-average precipitation is possible for December through February, she said.
“Should the cooler temperatures pan out, much of this could fall as snow,” Zimmermann said. “The southern half of Indiana will even be more likely to see increased precipitation, though the somewhat warmer conditions farther south might yield more rain or possibly even more ice events.”
Prof. Zimmermann may be reached at pazimmermann@bsu.edu.