DES MOINES — The weather experts say we’re fully out of the La Nina pattern now but haven’t yet transitioned into El Nino, which could gradually bring about significant changes in Iowa’s seasonal temperatures, rainfall and snowfall.
State climatologist Justin Glisan says an El Nino Watch is now posted and sea surface temperatures are near-normal, but changes are coming. “The surface temperature anomalies are trending warmer, though ocean and atmospheric coupling has not occurred,” Glisan says, “so for El Nino to actually come to fruition, the atmosphere has to respond to those warmer sea surface temperature anomalies in the eastern Pacific and we haven’t seen that yet.”
An El Nino pattern typically means Iowa sees more moderate temperatures and better chances for precipitation. Glisan says the computer models show it will arrive soon, perhaps within weeks. “If we look at the modeling, the transition to El Nino is expected in late spring into early summer,” he says, “and we have higher probabilities of that pushing into a northern hemisphere winter.”
Glisan says forecasters are getting a better idea of the intensity of the incoming El Nino. “In the April-May-June timeframe, we start to see the modeling go above the El Nino threshold, so those warmer sea surface temperature anomalies,” Glisan says, “and then, as we get into late spring into summer, we start to see the model average converge around 68% probability of a El Nino occurring.”
Past El Ninos have led to cooler and wetter summers, with milder and less snowy winters in the Northern Plains.
Glisan moderated this month’s North Central Regional Climate update for the National Weather Service.