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Southern Heat and Drought Projected to Continue into Fall, Forecasters Say

At this point in the summer, many Texans are probably wondering if they’re ever going to see rain and cooler temperatures again. Across most of the state, it’s been a rough summer of severe drought and record heat, and according to recent forecasts from the National Weather Service (NWS), the region isn’t going to see much in the way of significant relief for several months.

A new temperature and precipitation outlook released yesterday by NOAA’s Climate Prediction Center shows that unusually warm and dry weather is likely to continue through the next three months. Similarly, a newly published drought outlook shows that states like Texas, Oklahoma, New Mexico, and Arizona should expect the current drought to continue, or even worsen. 

The latest US Drought Outlook, issued August 18, 2011. Brown areas show regions with expected drought persistence, with green areas showing expected drought improvement. The Climate Prediction Center has an annotated version of this image. Credit: drought.gov.

“This forecast is based partly on the possibility that La Niña may be coming back,” said Ed O’Lenic, a senior meteorologist at the Climate Prediction Center. Over the past several weeks, he says, sea surface temperatures in the tropical Pacific Ocean have been cooler than average, which may be a signal that La Niña is going to return for a second consecutive winter. Right now, O’Lenic says there is a 50 percent chance La Nina will develop again.

La Niña is a natural climate phenomenon characterized by cooler than average waters in the equatorial Pacific Ocean. The cooler conditions can influence global weather patterns, and during typical La Niña years the American Southwest tends to be drier than average. Scientists are researching how global climate change may affect La Niña and its sibling climate cycle, known as El Niño, but there is still a large amount of uncertainty.

This summer’s drought in states like Texas and Oklahoma is actually a “legacy of La Nina from last winter,” says O’Lenic. The unusually dry conditions developed last fall and winter, and have persisted well into the spring and summer of 2011.

Some parts of Texas have had a bit of rain during the past month, but as O’Lenic says, it hasn’t been enough to relieve the exceptionally dry conditions. “Going from the worst drought in many, many years to one that isn’t quite as bad isn’t much of an improvement,” he says. And while there is still a chance that a tropical storm or hurricane could roll in from the Gulf of Mexico and deliver enough precipitation to affect the drought, he says, “the drought conditions are likely to continue throughout the South and Southwest.” The rainfall deficit is just too large for one storm to overcome.

Temperature departures from average during July 2011, showing the unusual heat in Texas, Oklahoma, and much of the East. Credit: NOAA/NCDC.

As the climate warms, climate scientists also predict that precipitation extremes will become more common, ranging from severe droughts like this year’s in the South to more frequent heavy rainfall and floods, like those that battered the Mississippi and Missouri River basins earlier this spring. Earlier this year, researchers found that global warming has already made intense bouts of rainfall more common in parts of North America and Europe.

In the Southwestern U.S., which has long been prone to cycles of lengthy droughts, rising temperatures could make the region even drier. Yet, while this year’s drought in Texas has been rated the worst single-year drought since instrument records began more than 100 years ago, historical data looking back over more than a thousand years shows there have been dry spells much worse that what the region has seen recently.

Over the past few months, the drought contributed to the record-breaking heat that has gripped several southern states. Last week, the National Climatic Center (NCDC) released a climate report for July, showing that last month was the fourth-warmest month on record for the country. It was hottest month ever on record for both Oklahoma and Texas, and Oklahoma also set a new record for the warmest average statewide temperature for any state, at 88.9°F. Both states also experienced some of the lowest levels of July precipitation since the 1880s, which exacerbated the already devastating drought. Several cities in Texas have set new records for the most consecutive days with high temperatures at or above 100°F.

Across the entire U.S., nearly 3,000 daily high temperature records were broken during July, and more than 6,000 weather stations reported record warm overnight minimum temperatures as well, says Deke Arndt, chief of NCDC’s Climate Monitoring Branch. Furthermore, he says, 78 stations in the U.S. reported new all-time record high daytime temperatures, and 213 set new all-time records for the warmest overnight temperatures. 

When you consider how many stations reported temperatures that were within the top 10 percent warmest on record, Arndt says, in addition to the number that were truly record-breaking, “this was easily the most extreme July on record.”