Scorching June Heat Wave Puts 50 Million in U.S. on Alert

By Andrew Freedman

A scorching heat wave that began in the High Plains is baking the Central Plains, and on Friday prompted warnings for the big cities of the Mid-Atlantic and Southeast. The combination of triple-digit heat and high humidity has prompted the National Weather Service (NWS) to issue heat warnings and advisories for at least 18 states from Kansas to New Jersey, south to Mississippi, putting at least 50 million people under some form of a heat alert.

Map of land surface temperature departures from average, as detected by a NASA satellite. Credit: NASA.

Heat watches and warnings are in effect for major metro areas such as St. Louis, Indianapolis, Columbus, Nashville, Charlotte, Raleigh, Richmond, Washington, D.C., Baltimore, Philadelphia, and New York.

The heat wave has already broken numerous longstanding records, which in some cases dated back to the Dust Bowl era of the 1930s. Many of the records being set have been for warm overnight low temperatures. In Des Moines, for example, the low temperature on Thursday was a tropical 81°F, breaking the old record for the date of 78°F that was set in 1931. According to the NWS, this was just the second time in the past 75 years when the low temperature was 81°F or warmer in this location.

When temperatures fail to cool below about 80 degrees at night, the risk of heat-related illness in persons without access to air conditioning, particularly the elderly, goes up dramatically, according to public health experts. The National Weather Service has been stressing heat safety tips, reminding Americans that heat is the top weather-related killer, with hundreds of deaths each year. Smoke from the wildfires in Colorado and other Western states is adding to concerns about poor air quality in the East, with numerous air quality advisories in effect on Friday.

During the June 22-to-28 period, there were 2,132 warm temperature records set or tied in the U.S., compared to 486 cold temperature records. This includes 267 monthly warm temperature records, and 54 all-time warm temperature records.

For the year-to-date, warm temperature records have been outpacing cold temperature records by about 7-to-1.

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.

All-time records set Thursday included several in Kansas, where Norton Dam recorded a high of 118°F, beating the old record of 113°F set just a few days earlier. Dodge City, Kan., set a daily high temperature record with a mark of 108°F. That came one day after that town recorded its all-time highest temperature of 112°F, breaking the old record of 110°F, which had been recorded just two days earlier, on June 26.

St. Louis hit a blistering 108°F on Thursday, which was hot enough to set a monthly temperature record, breaking the previous mark of 105°F, which was first reached in 1936. Several other locations in Missouri also set monthly high temperature records on June 28, including Columbia, where the high was 107°F.

Indianapolis set a record for the highest temperature ever recorded during the month of June, with a high of 104°F. The old mark was 102°F, which was last recorded in 1988, the year that global warming first made national headlines.

Fort Wayne, Ind., tied its all-time highest temperature record of 106°F, with there's a forecast high of at least 100°F for Friday. Evansville, Ind., reached 107°F, which broke its record for the highest June temperature.

The heat is the result of a sprawling area of High Pressure aloft, centered over the South Central states, which is pumping warm air northward and keeping rain chances low to nonexistent. Severe thunderstorms have already erupted on the northern edge of the heat dome, in an area that meteorologists refer to as the “ring of fire,” a term that refers to the tendency for thunderstorms to form and then ripple along the boundary between extreme heat and cooler air to the north.

The latest heat wave comes during a year when the Lower 48 states have already set temperature records for the warmest spring, largest seasonal departure from average, warmest year-to-date, and warmest 12-month period, all new marks since records began in 1895. While the globe has been tracking slightly cooler than recent years — thanks in part to the influence of now dissipated La Nina conditions in the tropical Pacific — the U.S. has been much warmer than normal.