A look at weather extremes and the big-picture climate connections.

Stubborn 2012 Heat Wave Roasts Eight States

Like an unwanted houseguest, intense heat and humidity have overstayed their welcome in the South Central states from Kansas southeastward to Mississippi. For many parts of this region, triple-digit heat is likely throughout this weekend and into the first full week of August, with even more records falling by the wayside. 

Air temperatures in Oklahoma near midday on July 31.
Credit: Oklahoma Mesonet.

So far during July, hundreds of records have been broken in an eight-state hot zone that encompasses Arkansas, Kansas, Louisiana, Mississippi, Missouri, Oklahoma, Tennessee and Texas (track records using Climate Central’s Record Temperature Tracker). In addition, those states -- as well as many others across the U.S. -- continue to be hammered by drought as rainfall has been scarce.

Consider the case of Wichita, Kan., which has been battered by blistering heat. Just 0.26 inches of rain fell in Wichita through July 30, about 3 inches below average. In addition, the monthly average temperature through July 30 was a balmy 88.2°F, which was 7.3°F above average. The temperature reached 111°F twice, on July 29 and then again on the 30th. Every single day in July (including Tuesday) saw a high temperature of at least 90°F.

Those kinds of record temps played out across the South Central states. In Little Rock, Ark., the high temperature on Monday of 111°F was the hottest temperature recorded there since 1986, and the second-hottest July temperature on record. That reading was also the third-hottest temperature on record for that location, according to the National Weather Service. The average high in Little Rock on July 30 was 93°F.

At North Little Rock, the low temperature on July 30 of 83°F tied the record for the highest low temperature recorded in the month of July. And at Batesville, Ark., the low temperature on July 30 was a toasty 84°F, which set a daily record and broke the record for the highest low temperature for the month of July. It also tied the all-time highest low temperature record.

Heat index forecast for August 2, showing heat indices of 105+ Fahrenheit persisting in the South Central states. Click on image for a larger version.
Credit: NOAA.

In Tulsa, Okla., an all-time record warm low temperature was recorded on July 30, when the temperature failed to drop below 88°F, which is close to the average high temperature for the date! The NWS continues to warn people in central Oklahoma to be prepared for heat index values exceeding 105°F, which can be extremely hazardous for human health. Heat is the No. 1 weather-related killer in the U.S.

Not only is the heat causing problems for people, it is also causing critical weather monitoring equipment to break down. On July 29, the National Weather Service reported that the Doppler Radar in Ft. Smith, Ark., had to be shut down due to extreme heat and air conditioning problems, and on July 30, the NWS in Tulsa reported similar trouble with their Doppler radar equipment. Such radar units are crucial for monitoring severe thunderstorms and tornadoes, among other weather-related hazards. Fortunately, or rather unfortunately, since these areas desperately need the rain, severe thunderstorms have been in short supply lately.

The heat is exacerbating the extreme drought conditions while also feeding off the parched soil, since dry conditions can lead to more heat extremes. Through the end of June, the South has had the most extreme weather during this period since the Climate Extremes Index began in 1910, with 56.86 percent of the region affected by extreme weather. Record warm temperatures and far below-average rainfall were the main drivers behind this record, according to the NWS.

The record heat continues what is already a record warm year in the U.S., and a sizzling and parched summer. The warm July follows a warmer than average June, which came on the heels of the warmest spring on record, which in turn was the culmination of the warmest March, third-warmest April, and second-warmest May. This year marked the first time that all three months during the spring season ranked among the 10 warmest, since records began in 1895.

NOAA Climate Extremes Index for the South from January through June of 2012. According to NOAA, extreme weather has affected a greater portion of the South so far this year than any other year in the century long record.

In a long-term trend that demonstrates the effects of a warming climate, daily record-high temperatures have recently been outpacing daily record lows by an average of 2-to-1, and this imbalance is expected to grow as the climate continues to warm. According to a 2009 study, if the climate were not warming, this ratio would be expected to be even.

On shorter timescales, record temperature imbalances can be much more significant, and this year-to-date, record daily highs have been outpacing record daily lows by a ratio closer to 9-to-1. Or, when you look at all warm temperature records, including overnight low temperatures compared to all cold temperature records, the ratio is closer to 7-to-1.

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