Dear Tom,
I was reading a report on the July 1995 Chicago heat wave. It noted there were no clouds over that period. Was there a capping of the environment that caused the lack of clouds?
Dr. Kenneth Thompson Ogden Dunes, Indiana

Dear Dr. Thompson,
There absolutely was a strong-capping environment during the tragic 1995 heat wave. Extensive high-pressure ridging, both surface and aloft, resulted in sinking air over the region that inhibited cloud formation, despite oppressive dew points in the upper 70s and lower 80s. Those high dew points combined with triple-digit temperatures, produced heat indices as high as 125 degrees, that ultimately resulted in more than 750 fatalities. During the peak of the heat wave, from July 13-15, Chicago climatologist Frank Wachowski reported that the city logged 90 percent of its possible sunshine.