Out with La Niña, in with El Niño?
El Niño or La Nina: Which will stand up and take control of this summer's crop weather in the Midwest?
The weather-forecasting community has spent recent weeks looking for a signal on the direction and strength of the El Nino/Southern Oscillation (ENSO), the measurement determining which prevailing system -- La Niña or El Niño, both of which with distinctly different consequences to crop production -- will drive the weather during this year's growing season.
Spring and summer moisture in the Corn Belt is typically lower in a La Niña system than during El Niño. Higher temperatures, at least in the Midwest, often accompany those drier conditions.
Right now, we're sitting at "ENSO-neutral," says National Oceanic & Atmospheric Administration (NOAA) meteorologist Klaus Wolter. That means it could go either way. The data right now shows a move away from La Niña -- a good thing for Corn Belt crop yield potential, generally -- is likely in the cards. Whether that will unfold into an altogether shift to El Niño or just a "disappearance" of La Niña has yet to be seen. And, there's quite a difference between the 2.
"La Niña has gone through a second-winter stage similar to 2008-09, and consistent with expectations formulated right here in late 2010: big La Niña events have a strong tendency to re-emerge after 'taking time off' during northern hemispheric summer," Wolter says. "Based on the evolution of recent atmosphere-ocean conditions, the MEI has obviously already reached ENSO-neutral conditions, with little chance of dropping back into La Niña conditions any time soon. There is a distinct possibility that we could see a switch to El Niño over the next three to six months. However, all multi-year La Niña events of the last 13 years have shown a tendency to weaken or even disappear during this time of year."
On Monday, Iowa State University ag meteorologist Elwynn Taylor said he expects La Niña to stay in effect for just under 2 more weeks. But, by April 22, a shift to ENSO-neutral conditions will likely lead to "a neutral growing season (normal crops) and possible shift to El Niño by August or later," he says.
Despite the observed shift away from La Niña, it hasn't meant a change in the outlook for temperatures and precipitation so far. University of Nebraska Extension irrigation engineer C. Dean Yonts is in the Panhandle of western Nebraska, an area where moisture's closely guarded and irrigation is a necessity. He says though rivers and waterways are at levels near their capacity, it's not a time to take those resources for granted, as it may not take much time for that to change. The reservoirs on the North Platte river system in Nebraska, for example, are just 400,000 acre-feet short of their total 2.5 million-acre-foot capacity.
"Irrigators in the North Platte River valley should remember that just a few years ago these reservoirs were just about empty, but then refilled to capacity in about a year. What happens if the dry conditions we experienced just a few years ago return not only in the coming year but into the next several years. If you look at long-range forecasts, temperatures in April are forecasted to be above normal," Yonts says. "In fact, if you look at long-range forecasts for the next year, there is a greater chance for above normal temperatures than average temperatures. Maps indicate equal chances for above or below normal precipitation, except during the 2012 harvest season, when above normal precipitation is predicted."