News•July 2, 2012

Heat Wave Continues As Storm Cleanup Drags On

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Andrew Freedman

By Andrew Freedman

A heat wave will drag on for yet another week in parts of the U.S., with more record warm temperatures likely in the Upper Midwest, High Plains, and the Carolinas. Meanwhile in the Mid-Atlantic, cleanup efforts are still underway after fierce thunderstorms ripped through the region on June 29, knocking out power to more than 3 million people and killing 17.

Although the scorching heat that had set at least 155 all-time high temperature records across the country between June 24-30 retreated from some areas on Monday, the overall weather pattern remains favorable for extreme heat to build right back in as the week goes on. This is bad news for people who still don’t have power, including hundreds of thousands of Mid-Atlantic residents. Utilities are working to restore electricity after one of the most destructive severe thunderstorm events in years felled trees and power lines from Indiana to Virginia.

Forecast heat index for July 4, 2012, showing intense heat in the Plains states and from the Carolinas to the Mid-Atlantic. Click on the image for a larger version. Credit: NOAA.

The complex of storms, known as a “derecho” event (pronounced “der-AY-cho”), caused destructive winds as strong as 92 mph, which is well above hurricane force. Unlike an actual hurricane, which can be tracked and forecast accurately days in advance, utility companies, emergency management officials, and the public had a maximum of a few hours notice that severe weather was on its way.

“Unlike a polite hurricane that gives you three days of warning, this storm gave us all the impact of a hurricane without any of the warning of a hurricane,” Maryland Gov. Martin O'Malley told reporters.

The extreme heat has been fueling the severe weather, including the derecho event as well as an intense thunderstorm that struck the Chicago area on July 1, knocking out power to 200,000 people there.

On Monday, the heat will be centered on the Southeast and Upper Midwest. The high temperature in Minneapolis is forecast to exceed 100°F, which only happens about three times a decade, according to meteorologist Paul Douglas, who writes a blog for the Minneapolis Star Tribune.

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“We've run out of adjectives. Tropical? Incandescent? Torrid? Swamp-like! None of them quite work today,” Douglas wrote.

Fewer high temperature records were set on Sunday compared to the last several days of June. Louisville hit 103°F, breaking a daily high temperature record of 99°F. Bowling Green, KY was a toasty 105°F, breaking its daily high temperature record of 102°F, which was set in 1941, and Lexington broke its daily record of 98°F by several degrees, topping out at 103°F.

A technical discussion from the National Weather Service did not offer much hope that cooler conditions will prevail during the week.

“HOT AND HOTTER WILL CONTINUE TO BE THE STORY FROM THE PLAINS TO THE ATLANTIC COAST THE NEXT FEW DAYS,” forecasters wrote. “THE WIDESPREAD EXCESSIVE HEAT WARNINGS AND HEAT ADVISORIES HAVE CERTAINLY DECREASED IN COVERAGE…BUT TEMPERATURES WILL REMAIN WELL ABOVE NORMAL ACROSS A LARGE PORTION OF THE U.S.”

Long-range forecasts show extreme hit continuing to affect the Plains, with triple digit temperatures likely, while the Northeast and Mid-Atlantic may finally cool off a bit. This is bad news for places like Hill City, KS, which hit 115°F on during the last week of June. The heat combined with drought conditions is causing serious problems for farmers, and there is no sustained relief in sight in the form of either rainfall or cooler weather.

Record temperatures set or tied on June 30, 2012, from the Climate Central Record Tracker.

The heat wave that is now extending into early July has been remarkable in its intensity and geographical scope. Consider that during just the June 25-July 1 period, 1,851 daily high temperature records were set or tied in the U.S., along with 609 record warm overnight lows. This compares to 149 record cold daily highs, and 267 record cold overnight lows during the same period.

Of these records, 157 were all-time high temperature records, and nine were all-time records for warm overnight low temperature. In fact, most of the year's all-time high temperature records were set or tied during the ongoing heat wave.

The year-to-date has seen at least 21,969 record daily highs set or tied, and 18,180 records for warm overnight low temperature. By comparison, only 3,395 records have been set or tied for cold daily high temperature, and just 2,443 records for cold overnight low temperature. This translates to a ratio of about 7-to-1 in favor of warm temperature records. 

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. Other studies have shown that climate change increases the odds of extreme heat events and may make them warmer and longer lasting.

Here are some of the noteworthy temperature records that were set or tied during this heat wave so far:

It is unusual for all-time high temperature records to be set or tied during June, rather than July or August, which tend to be warmer months on average. According to the Weather Underground’s Christopher Burt, in the region from Missouri to Maryland and south to Georgia, 95 percent of the all-time high temperature records were set during July and August.