By Gary McManus
La Nina has officially returned to the equatorial Pacific waters and that gives strong likelihood to the continuation of the drought in the southwest.
The climate phenomenon, marked by cooler than normal waters off the west coast of South America, has been named as one of the primary culprits behind 2011's extreme weather, such as the record flooding in the Northern Plains and the disastrous drought in the Southern Plains.
While that La Nina faded throughout spring before ending in June, the National Weather Service's Climate Prediction Center issued a La Nina Watch during August when the possibility of its return increased.
Data now show that La Nina returned last month, prompting the issuance of a La Nina Advisory by the CPC. Current long-range forecasts indicate a gradual strengthening of La Nina and its impacts throughout the fall into the winter should be expected.
"This means drought is likely to continue in the drought-stricken states of Texas, Oklahoma and New Mexico," says Mike Halpert, deputy director of the Climate Prediction Center in a National Oceanic and Atmospheric Administration.
The shifting of air patterns in the equatorial Pacific due to La Nina can lead to the disruption of normal weather patterns across the globe.
The impacts most common in the United States are above normal temperatures and below normal precipitation across the southern one-third of the country and cooler and wetter than normal weather in the Pacific Northwest and Ohio Valley.
The impacts due to La Nina are normally strongest from late fall through early spring in the Southern Plains, although not every La Nina produces the typical impacts. The return of La Nina is particularly troubling news for Oklahoma, Texas and New Mexico.
In Oklahoma drought has caused an estimated $2 billion in agricultural losses. Wheat, cotton and cattle operations have been particularly hard hit since last fall.
According to data from the Oklahoma Mesonet, the January through August statewide average rainfall total was 14.16 inches, nearly 11 inches below normal and the second driest such period since records began in 1895.
McManus is associate state climatologist for the Oklahoma Climatological Survey.