Last week will almost certainly go in the books as the hottest stretch of this summer. This big heat had been waiting patiently in the Midwest for most of July, biding its time to move this way.

Here's how temperatures across the U.S. for July compared to averages for the month. The maroon areas were warmer than average, while the blue that covers much of the East indicates that July was cooler than average for us. The dominant jet stream flow in July looked like this. Because the jet stream typically lies at the boundary between warmth to the south and cold to the north, this kind of pattern meant that we were on the edge of the big heat for most of July - and we did have a few minor hot spells broken by occasional visits from cooler, drier air.

Last week the jet stream moved north into Canada, leaving most of the lower 48 states knee-deep in record-setting hot air. If you're now tired of the big heat, take heart - it looks like we'll be shifting back into a more seasonable pattern for the rest of the month.