NASA satellite imagery shows the 2009 El Niño. Red and white areas were 4-7 inches above normal sea level while blue and purple areas were 3-6 inches below normal. Sea surface height indicates temperature change as water expands and contracts.

Long-range weather forecasters expect an El Niño return sometime this year but its timing and strength are still beyond the reach of reliable predictability.

Odds for an El Niño occurrence increase as temperatures warm in the Pacific. Above-average sea surface temperatures are currently being measured over much of the eastern tropical Pacific.

The El Niño–Southern Oscillation (ENSO) affects the location of the jet stream, potentially altering rainfall patterns across the West, Midwest and Southeast.

The National Weather Service’s Climate prediction Center currently puts the chances of an El Niño occurrence by summer at 50 percent and 65 percent by fall.

The Australian Bureau of Meteorology last week predicted a 70 percent chance of an El Niño in the next four months.

At this point, however, most prognosticators expect El Niño to have little affect on Midwestern fall crops.

The most recent summer El Niño occurred in 2009 when the June-August period was cooler and, at times, wetter than normal — and the U.S. produced record corn and soybean crops.

Current indications, however, suggest that if El Niño occurs, it’s significant weather impacts are more likely to happen in the fall.

Anthony Barnston, chief forecaster for the International Research Institute for Climate and Society, recently said in an ABC News interview that although the timing and the intensity is still difficult to predict, conditions are right for an El Niño return.

“We have above-normal temperatures in the tropical Pacific Ocean and that often precedes an El Niño because there’s a large volume of above-average water temperature below the surface of the ocean,” Barnston said. “Volume often tends to come up to the surface; often, but not always.”

“That’s the uncertainty,” Barnston said. “It’s more likely to rise than not.”

Barnston suggested El Niño will likely occur between April and June and last until the start of 2015.

ENSO-neutral is favored for Northern Hemisphere this spring, according to the Climate Prediction Center but the Center’s most recent ENSO report indicates increasing chances but a high degree of uncertainty:

“The model predictions of ENSO for this summer and beyond are indicating an increased likelihood of El Niño this year compared with last month. Most of the models indicate that ENSO-neutral (Niño-3.4 index between -0.5°C and 0.5°C) will persist through much of the remainder of the Northern Hemisphere spring 2014, with many models predicting the development of El Niño sometime during the summer or fall.

“Despite this greater model consensus, there remains considerable uncertainty as to when El Niño will develop and how strong it may become. This uncertainty is amplified by the inherently lower forecast skill of the models for forecasts made in the spring.”

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