Slow moving storms and associated clouds on Thursday helped to isolate the most extreme heat index values to southeastern Iowa with places like Cedar Rapids briefly reaching the triple digits. The featured chart looks into the dew point climatology by air temperature during the month of July for Cedar Rapids. The chart nicely shows a fortunate feature of Iowa's summer time dew point temperatures with decreasing values found with the most extreme air temperatures. The reason why has to do with surface energy budgets and the requirement of more input energy to heat a higher water content air. It is also a sort of self fulfilling prophesy that drier air is able to more quickly heat and mix down warmer air aloft, so air temperatures can reach higher temperatures. The climatology plotted shows a bit of an inflection point near 95°F as the average dew point values start to decrease.