U.S. growers of fruits and vegetables can look forward to a relatively calm start to summer, but El Niño effects could be felt later in 2012.

A weak-to-moderate La Niña season ended in April, as tropical Pacific sea surface temperatures, sea level pressures and trade winds returned to neutral levels, according to a recent report from the World Meteorological Association.

Looking ahead, the end of spring and beginning of summer promised more relatively benign weather.

“The latest results from forecast models and expert opinion suggest that sea surface temperature anomalies will likely oscillate around neutral conditions” through July, according to the report.

Beginning in August, however, there is about a 50/50 chance that El Niño conditions could develop, according to the report. The uncertainty is due to questions about whether the Pacific will warm enough to cause changes in the atmosphere, a necessary condition for El Niños.

Climatologists surveyed in the report say there is little chance of a La Niña developing in 2012.

Both El Niños and La Niñas can produce extreme weather conditions. In El Niños, the U.S. Northwest, Midwest and Northeast can be warmer and drier than usual.

The effect in other parts of the country can be the opposite, with the Southwest and central and southern California experiencing more moisture than usual and the Southeast more moisture and cooler temperatures.

La Niñas often have the opposite effects of El Niños, with above average precipitation in the Midwest, the Rockies, Northern California and the Pacific Northwest, and below-average precipitation in the Southwest and Southeast.