Government scientists this morning announced that an El Niño - an anomalous warming of surface waters in the equatorial Pacific that spans thousands of square miles - was under way.

They said it would probably last through the winter. El Niño has widespread effects on weather in the United States, but its specific impacts around here are impossible to predict.

El Niño, however, is known to have a dampening effect on the U.S. hurricane season. El Nino generates powerful upper-air winds from the west that travel into the Atlantic Basin and can snuff out incipient storms before they grow into hurricanes.

El Niños reoccur roughly every two to five years, with the last one in 2006.

Its other positive effects can include drought-breaking rains in the Southwest and more rain in the Southeast, lowering the risk of wildfires in Florida.

But El Niños also have produced devastating storminess in California and Central and South America and disrupt marine life on the West Coast.

Around here, El Niño has coincided with both mild winters and big snowstorms, including one of 21.3 inches in 1983.