Today's featured chart looks into the frequency of having overcast skies at a given air temperature during June using period of record observations from the Des Moines Airport. It is always interesting when clear signals are found within plots like this one, but there is sometimes a quirk that is difficult to explain. The easy to explain signal is the decreasing frequency of overcast reports as the temperature increases into the mid 90s. Sunshine during June is certainly important to drive higher air temperatures and conversely cloud free skies to help support the most intense radiational cooling overnight events, but what is happening with the slight increase oin overcast frequency starting in the mid 90s? This likely has to do with the juxtaposition of these extremely warm temperatures only happening during the late afternoon hours and that such warm temperatures are likely driving developing thunderstorm activity off to the west, which increases overcast conditions as the clouds spread east aloft. For this weekend, mostly clear skies are forecast for Saturday with highs in the lower 90s.

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