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El Niño’s impact on South’s weather

Twenty years or so ago, I attended a conference on the west coast, at which a distinguished climatologist made a presentation on theories being developed about a weather phenomenon called El Niño.

It all sounded so far-fetched, the poor guy was nearly hooted off the stage.

Since then, El Niño has become an established weather event, with consequences that can be extreme, as farmers over the Mid-South and much of the Midwest learned to their sorrow last year.

El Niño occurs when surface ocean temperatures in the equatorial Pacific become warmer than normal, causing a disruptive effect in the atmosphere, pushing the jet stream off track, and creating unusual weather in other parts of the world, including the southern states.

A corollary phenomenon, La Niña, a cooling of the equatorial ocean temperatures, often disrupts weather over the Pacific Northwest and causes dry conditions across the South.

In 2009, the U.S. got both.

“Last year started with a La Niña, which was expected to change to an El Niño in the fall of 2009,” says Nancy Lopez, USDA physical scientist at Stoneville, Miss., who spoke at the annual meeting of the Mississippi Association of Crop Consultants. “Instead, the change occurred in April.”

Compounding the El Niño was a stationary boundary that constantly sent tropical storms over the area, producing extremes of very dry and very wet. At Stoneville, Lopez noted, January-April was very dry, followed by 13.5 inches of rain in May.

But, conditions were highly variable. “From January-June, at Stoneville, we received 27.21 inches of rain,” she says. “On an almost direct line across Highway 82, at Starkville, Miss., only 170 miles away, rainfall totaled 42.79 inches.

“Most of the state had a 6-inch differential during this period, either 6 inches short or 6 inches excess.”

June was abnormally hot across much of the area, with 3.75 inches of rainfall at Stoneville, while July was cool with above normal rainfall, 4.88 inches. October rainfall was record high, 15.51 inches, and the year’s total was 65.5 inches, 12.6 inches above normal.

“Some areas had totals in excess of 70 inches for the year,” Lopez says. Bolivar County, just to the north, reported 81.77 inches. The normal annual total for the state is 52-53 inches.

El Niño patterns occur irregularly; the Scripps Institution of Oceanography, which has done extensive research of the phenomenon, says every three to seven years. A strong El Niño can persist for a year or more.

The National Weather Service, at mid-January, said the current El Niño may continue at least until June, bringing above normal precipitation and hotter than normal summer temps.

Across the pond, British meteorologists are positing that 2010 may be the warmest year on record worldwide, thanks to El Niño. The last really strong El Niño occurred in 1998, they say, and was a key factor in making it the hottest year on record.


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