Today was the hottest day so far this summer with an afternoon high of 93F (34C) and a heat index of 100F (38C). It's a bit early to have such high temperatures. In 2008, the highest temperature of the year was 93F, but it didn't happen until September 3. In 2007, the maximum high for the summer was 96F on August 29. So perhaps this is a sign of the upcoming summer temperature pattern.
Check out the areas of poor air quality. The yellow shading indicates moderate air quality, the orange indicates unhealthy air for sensitive groups, and the red areas (Houston and Dallas, Texas) indicates unhealthy air for all groups. Today was a ozone action day in Indianapolis and Cincinnati. The cause of the air quality alert is due to the high temperatures and a still atmosphere. Without the wind to mix things up, the atmosphere becomes stagnant and ozone levels increase.
Click on the photo below for a larger view. It was taken earlier this month from the International Space Station as it was flying over an erupting volcano in Japan.