Summer of 2012 Is Hottest on Record For Many in U.S.

The books have closed on meteorological summer, which encompasses the June-through-August period, and the data that is starting to trickle in from the National Weather Service shows that tens of millions of Americans experienced their hottest summer on record. 

The National Oceanic and Atmospheric Administration (NOAA) has not yet announced whether the lower 48 states had its warmest summer on record, but after July set a record for the warmest month in recorded history, it’s quite plausible that the summer as a whole was the warmest such period as well.

Map of surface temperature departures from average during July 2012, showing how the U.S. was unusually warm. Click on the image for a larger version. Credit: NASA GISS.

For cities like Milwaukee and Detroit, it was the hottest summer on record. And many other locations had one of their top five warmest summers.

In Minneapolis-St. Paul, it was the third-warmest on record, behind the summers of 1988 and 1933. July was the second-warmest month on record in the Twin Cities, thanks to a long-duration heat wave that gripped much of the Central and Eastern states, breaking thousands of longstanding temperature records. August was the 15th straight month with above average temperatures in the Twin Cities.

Like many cities, the Twin Cities have had their warmest year-to-date on record, beating 1987 by more than 1°F, an unusually large margin.

In St. Louis, which has also had its warmest year to date, there were a record 11 days this summer when temperatures reached or exceeded 105°F, and the National Weather Service stated that the records for 90-degree plus days as well as other longstanding temperature records may fall by October. St. Louis experienced 21 100-degree days this summer, tying for fourth on its all-time list.

Chicago also sizzled, with its third-warmest summer, behind 1955 and 1995. The average temperature was 4.3°F above average, and the city recorded 40 days with temperatures of 90°F or above. In Columbus, there were 44 days with high temperatures of 90°F or above, breaking the record of 42 days, set in 1944.

In Washington, D.C., this summer was the third warmest on record, and this year has been the warmest of any on record so far.

While the West Coast was a lot cooler than the rest of the lower 48 states this summer, the region did get in on the warmth during August. Reno, Nev., and Fresno, Calif., set records for the warmest August, for example.

Map showing the extent and severity of the drought conditions in August 2012. Click on the image for a larger version. Credit: NOAA.

During the June-through-August period alone, there were a whopping 9,685 daily record high temperatures set or tied in the U.S., compared to just 2,260 record daily lows. 

As Climate Central reported in August, record daily high temperatures through August 5 eclipsed the number of record daily highs set during all of 2011, a remarkable feat. For the year, record daily highs have been outpacing record daily lows by a ratio of about 6-to-1, which reflects the trend identified in a 2009 study on how temperature records are changing as the climate warms.

A recent study found that the odds of extremely hot summer temperatures are increasing dramatically due in large part to manmade global warming.

In addition to the heat, the big weather story this summer was the punishing and extremely expensive drought that rapidly intensified and expanded across much of the U.S. The heat helped worsen the drought by drying out plants and soils faster, while the dry conditions in turn helped boost temperatures ever further, powering a so-called positive feedback loop that contributed to the records set this summer. The drought has eased slightly in recent weeks, but is forecast to linger in some areas for the next few months at least.

The warm summer continues the drumbeat of much warmer-than-average U.S. weather so far this year, with the warmest spring on record following a mild winter. During spring, the U.S. saw its warmest March, third-warmest April, and second-warmest May.