Long-range weather forecasters are calling for a continued scorching of Texas and the rest of the U.S. Southwest, and they blame it on an old favorite--El Niño. Despite its apparent demise late last spring, the unusual warmth of tropical waters has lingered in the eastern Pacific long enough to drive summertime drought in the Southwest. And when El Niño takes its final bow in the next month or two, its opposite number, La Niña, will take the stage, forecasters say, and likely keep the Southwest dry through next winter.
In a special report issued late last week, meteorologists at the National Weather Service's National Centers for Environmental Prediction (NCEP) in Camp Springs, Maryland, explain how El Niño appears to have kicked off the looming drought last January. According to computer models and analysis of weather maps, the tropical atmosphere cranked up high-altitude winds that arced northward and dried out as they descended over Central America and Mexico, parching those regions--a classic wintertime response to the ocean warmth of El Niño. As expected, that enhanced airflow also sent winter storms straight across the southern tier states and soaked them.
But this spring, in a twist that caught forecasters by surprise, the dry, descending air persisted and shifted northward. That brought Mexico's dryness to Texas and pushed the winter's wet storminess to the north. Now it's up to NCEP forecasters to figure out the tropical Pacific's next move. "We're expecting this warm water to peter out in the next 3 to 6 weeks," says NCEP's Anthony Barnston. Then, by winter, El Niño should be replaced by La Niña--cooler than normal waters across the tropical Pacific--that traditionally brings dryness to the southern tier. "If we don't get more normal precipitation in the late summer and early fall, we're looking at a very large [drought]," says Barnston.