The past three years have been dominated by a La Niña weather pattern, but models are showing that may finally be coming to an end.
Iowa State Climatologist Justin Glisan, speaking to a group of producers at the Iowa Ag Expo Feb. 1 in Des Moines, said this is the third time since 1950 where La Niña has stuck around this long. As the months move on, he said the time frame of March, April and May has a high probability of shifting from La Niña to a more neutral pattern. The probabilities start shifting toward El Niño the further the forecast goes.
“It’s showing an 82% chance of a transition through then,” Glisan said. “If we look at that time frame, precipitation behavior is usually above average or more. There is more precipitation usually in a neutral pattern.”
Models are showing a higher probability for slightly cooler temperatures across the upper Midwest this spring and a wet signal across the Ohio Valley shifting into Iowa with near normal precipitation conditions across western Iowa and a dry signal across the Upper Midwest.
“That’s a few good signals to see as we transition from La Niña to neutral,” he said. “Oceanic waters are trending back towards where they should be or near normal. We are seeing a shift of higher probabilities of wetter conditions into eastern Iowa.”
As of the January 19 three-month outlook, the furthest out the National Oceanic Atmospheric Association goes, eastern Iowa, eastern Missouri and all of Illinois have higher probabilities of above normal precipitation through April. Western Iowa and western Missouri are showing equal chances of above or below normal precipitation.
In terms of temperature, the Iowa, Missouri and Illinois regions are all showing equal chances above or below normal.
Glisan also noted that Iowa is emerging from its 25th driest year in the last 150 years, and while that drought is being felt in western Iowa, Missouri and southeast Iowa, it isn’t the common theme throughout the region.
“This is interesting because when you have a dry year there’s an absence of thunderstorms, clouds and warmer temperatures,” he said. “We haven’t really seen that. That’s been the saving grace in terms of drought all across the state.”
One trend Glisan noted independently of the La Niña shift is how the growing season is getting longer for farmers in the Midwest. While that is not necessarily a bad thing, the stretched out season hasn’t come with as much moisture.
“It’s anywhere from 10 to 14 days longer, he said. “While that’s good news in terms of planting hybrids and picking what you want to plant, July precipitation has declined. So we are not seeing as much rainfall as we normally get during tasseling maturity.”
While July rainfalls have declined, making the middle of the growing season drier, August rainfall has increased overall, Glisan said.
