News•August 5, 2011

Records Fall During Extended Heat Wave

Record-breaking heat and drought have spread across several southern states, including Oklahoma and Texas. The National Weather Service issued heat warnings or advisories for parts of 15 states across the South this week. Credit: Al Jazeera.

As hot weather continues to bake much of the county’s midsection, the National Weather Service issued heat advisories and extreme heat warnings for parts of 15 southern states yesterday. Across states like Texas, Oklahoma, Arkansas, and Mississippi, temperatures set new daily high records, adding to the tally of thousands of temperature records that were broken so far this summer across a wide swatch of the country.

Here are some of the most striking records set during the past week:

On Wednesday, the mercury hit 115°F in Fort Smith, Arkansas, which shattered the all-time record of 107 degrees, set back in 1896. Fayetteville, Ark. hit 110°F on Wednesday, which broke the 47-year-old record of 102°F. Little Rock also set a new all-time record high temperature, at 114°F.

July 2011 was the warmest month on record in Lubbock, Texas. This year, the city has already had at least 34 days with temperatures at or exceeding 100°F, which breaks the previous record of 29 days set during the “Dust Bowl” era. With most of August still to come, this new record will probably end up even higher.

Tyler, Texas hit a record-breaking 36-day streak of triple-digit temperatures on August 2. Dallas-Ft. Worth has had 34 straight days with temperatures above 100°F (the second longest streak for the area).

It was also the hottest July on record in Oklahoma, where the state’s average temperature was 89.1°F. That’s more than seven degrees above average for July, and 1°F warmer than the previous record set in 1954.

Most of extreme southwestern Oklahoma has had 43 consecutive days or more with temperatures above 100°F, and the streak is expected to continue well into August. On average, this region expects 30-40 days above the century mark each year. According to Gary McManus, Oklahoma associate state climatologist, the highest number of 100°F days ever in one year is 86, set in Hollis in 1956:

“With a month still to go in the summer, we’re approaching that record rapidly.”

The current heat wave comes on the heels of a very hot July across much of the country (with the noteworthy exception of the West Coast). During the month of July, 2,722 weather stations in the U.S. reported record daytime high temperatures. There were also more than 6,000 locations where the overnight low temperature either tied a record or was warmer than it had ever been on a given day.

Tying or breaking daytime high and overnight low temperatures isn’t that unusual. What’s incredible is that there were 443 places in the U.S. where the overnight temperature was warmer than it had ever been, on any day in recorded history. And there were 763 places where the all-time daytime temperature was broken.

US drought monitor, showing the widespread “extreme” to “exceptional” drought conditions in Texas, Oklahoma, and New Mexico, and less severe drought extending eastward along the Gulf Coast.

The astonishing heat hanging over Texas, Oklahoma, Arkansas, and several other South Central states is partially related to the region’s ongoing drought. As shown in the U.S. Drought Monitor, this year’s parched conditions are among the worst on record, and that’s contributing to the excessive hot weather (it’s also a factor in this spring’s record wildfire season).

Normally, much of the sun's heat goes towards evaporating moisture from the soil and plants, which helps keep the air cool. But this summer, with less moisture available, nearly all of the sun's energy is being directed at heating up the air. Moreover, parts of Texas and Oklahoma haven’t seen rain in weeks or even months, so there’s been little relief from the persistent heat.

Over the next couple of months, the National Weather Service has forecast that drought conditions will hang on in much of the South, and may even intensify in some places. And according to climate science research, rising greenhouse gas levels in the atmosphere are projected to make severe drought and record heat waves like this one more common in the Central Plains in the coming decades.