With rumbling thunderstorms living up to their name this Friday morning, the featured chart shows the climatology of thunder reports based on the Des Moines Airport weather station. The chart is a histogram showing the frequency by week of the year and hour of the day. For hour of the day, it nicely shows two peaks at about 9 PM and at 4 AM (coincidentally when thunder is occurring now this morning!). The 9 PM peak represents the thunderstorms that fire during the late afternoon hours thanks to intense heating and instability that builds during the day. The 4 AM peak is driven by something called the Low Level Jet, which feeds thunderstorm complexes into the early morning hours that roll through Iowa during the summertime. For week of the year, the weeks of June are the peak which is a function of having the highest combination of instability and shear.

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Tags:   thunder