The culprit for the dry weather that has parched much of the Midwest may be fading, a University of Missouri atmospheric scientist said. But don’t expect much relief, yet. The dry soil will have an impact on this summer’s temperatures.
Tony Lupo, department chair of Soil, Environmental and Atmospheric Sciences at the College of Agriculture, Food and Natural Resources, said that the La Niña weather pattern – the Midwest’s toasty weather influencer for more than two years – has diminished.
That’s the good news. The not-so-good news is that while La Niña has faded, it hasn’t been fully replaced by El Niño that brings more moisture and cooler temperatures to the Midwest. Lupo said climate and historical data suggests the Heartland has entered a neutral period that could persist through late summer 2013.
This will bring more moisture to much of the Midwest, but at still below normal levels. A late summer pickup in normal rain will be too late for much of the next growing season, Lupo said.
A Change in the Pacific
La Niña and El Niño are regularly occurring climatic features, often changing places every few years.
During La Niña, sea surface temperatures across the equatorial Pacific Ocean are lower than normal by 3–5 °C. This typically directs the jet stream from the Pacific on a northeastern path over Canada. Rain producing storms follow the jet stream, leaving the central and south-central states dry. This route of the jet stream also blocks arctic air from moving south into the American midsection, resulting in higher temperatures.
Even if a neutral or El Niño weather patterns mutes the warmer trend in the Midwest, the dry soil left over from multiple years of drought will still result in higher-than-average summertime temperatures, Lupo said. Soil moisture influences air temperature. High soil moisture produces high evaporation, producing evaporative cooling. Without this evaporative cooling, daytime temperatures could be as much as 10 degrees higher, Lupo said.