(Atlantic) Iowa State Climatologist Justin Glisan says there is an 80-percent chance of the current Enso-neutral weather pattern transitioning to La Nina. Glisan says El Nino is a warm phase, and La Nina is the cold phase.
Glisan says we’re currently in an ENSO Neutral, which is between the warm and the cold phase, or near-normal sea surface temperature anomalies in the tropical Pacific. The same pattern transitioned from Winter to Spring last year.
“When we do see a transition from ENSO Neutral to La Nina as we did this year, we get a double-dip La Nina, or a La Nina forming in the fall into Winter,” explained Glisan.
Glisan said this ENSO weather behavior would determine where thunderstorm activity sets up over the Pacific. In the La Nina phase, he says thunderstorms are further west and affect the jet stream over the United States, impacting temperature and precipitation.
“Typically, when we see a La Nina transition in the fall, we see above-average temperatures, and that’s what we see in the outlook,” said Glisan. “The initial outlook is showing us a pretty good chance of above-average temperatures across much of the United States from late September through October.”
Glisan says precipitation is highly variable during a transition back to a La Nina. He told me the precipitation signal is not clear at this point, and the sign will become more known as we head into the winter months.
“When looking at the precipitation maps during La Nina years, there is a bullseye for wetness over the Ohio Valley and the Pacific Northwest, and a dry signal for much of the southern states,” said Glisan. “Iowa happens to be in the middle of that interface. But if we look at last winter’s La Nina behavior, we were near average in terms of precipitation and warmer than average.”
Glisan said precipitation chances would become more apparent as we approach the winter months.
