An unusually massive high-pressure system that's stalled over the center of the country is sending temperatures so high they're blowing the mercury out of thermometers nationwide. Heat records are being shattered in cities from Texas to Minnesota, and electric utilities are straining under the heavy demand from thousands of air-conditioning units. Here, a guide to the "oppressive" 2011 heat wave:

Just how bad is this heat wave?
Worse than anything we've seen in a long time. "Through July 16, 969 daily high temperature records were either tied or broken in the country, including 12 all-time highest temperature records," says Andrew Freedman at The Washington Post. Most of those records were broken in Arkansas, Kansas, and Oklahoma, in the center of the immense heat dome that's covering the nation's midsection. At least 22 deaths have been blamed on the heat wave, and it's not expected to end for several days.

What exactly is this heat dome?
"Vast amounts of warmth and moisture have been trapped under a huge 'heat dome,'" says the Associated Press. That dome is created when "a high-pressure system develops in the upper atmosphere, causing the air below it to sink and compress because there's more weight on top." The result is higher temperatures in lower parts of our atmosphere.

Are high temperatures confined to the central U.S?
No. The high-pressure system has been creeping eastward, and is expected to park itself over the Atlantic Seaboard for the next few days. "It's hot today, but it's going to be hotter later in the week," says Jim Keeney, a National Weather Service meteorologist, as quoted by Reuters. By the weekend, however, temperatures are expected to begin dropping somewhat.

Is this heat dome caused by climate change?
Perhaps. But there's no hard evidence that a summer heat wave in one region is caused by a global shift in climate. "While climate change may well have contributed to whatever is going on, it can’t be definitively fingered as the sole cause," says Alyson Kenward at Environment360. Climate scientists, however, are predicting that if greenhouse gases continue to increase in the atmosphere, we're going to be seeing a lot more of this kind of extreme summer weather.

Sources: Associated PressCNN, Environment360, Reuters, San Francisco Chronicle, Stanford University News, Washington Post