Winds were gusty over the weekend thanks to stronger contrasts in air masses over the US with a more fall like weather pattern in place. On Sunday, these gusty winds were also helped by strong mixing of the lower atmosphere that transports higher momentum air to the surface during the daytime. You may have noticed the winds slacking after the stabilization of the atmosphere after sunset Sunday evening. This mixing of air aloft tends to also decrease humidity levels as near ground surface moisture is diluted with drier air. So it stands to reason that relative humidity would decrease as surface winds increase as is nicely shown by the featured chart of average relative humidity by wind speed during September for Des Moines. You may wonder though why values start bouncing around and even increasing with around 25 knot wind speeds and higher? This is due to a smaller sample size that is dominated by convective events (ie thunderstorms). These events will feature higher humidity values as it is typically raining with the storms!

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