Two Images Tell the Story of 2012 Heat and Epic Drought

For the tens of millions of Americans who suffered from the punishing heat and drought during July, it probably comes as no surprise to learn that the two hazards were closely related. Both the unusually dry weather and the deadly heat resulted from the same weather pattern that set up across North America during the spring and summer, with a huge area of High Pressure, or a “heat dome,” parked above the South Central states, pumping warm air northward and banishing storms that could have dropped beneficial rainfall.

As you can see from these two graphics, the hottest areas in July were also some of the places that were caught in the grips of the most severe drought conditions. Because the ground was so dry, very little evaporation took place from the land surface and plants into the atmosphere. This meant that more of the sun's energy was able to go into directly heating the air, and the drier than usual conditions helped air temperatures climb higher than they otherwise would have. A whopping 4,420 daily high temperature records were set or tied during July, along with 3,673 warmest-overnight low temperature records. A total of 32 states had July temperatures among their 10 warmest, with seven states having their second warmest July on record.

Map of temperature departures from average for the month of July. Click on the image for a larger version.
Credit: NOAA Visualization Lab.

A NOAA visualization showing drought conditions across the country as of August 9, 2012. The darker red areas depict the regions where the drought is most intense. Click on the image for a larger version.
Credit: NOAA Visualization Lab.

July was the warmest month on record in the U.S. The average temperature for the month came in at 77.6°F overall, which was 3.3°F higher than the 20th-century average, and 0.2°F warmer than the previous hottest month on record, set in July 1936 back in the Dust Bowl era. This came at the same time as the so-called drought footprint—the area of the country affected by drought conditions—reached a record high, and the worst drought since at least 1956 laid waste to hopes for a bumper corn and soybean crop, spurring the Agriculture Department to issue the largest-ever disaster declaration in its history.

As Climate Central reported, there have already been more record daily high temperatures set or tied so far this year than were set or tied during all of 2011. And 2011 had the second-warmest summer on record for the lower 48 states.