The widespread frost / freeze this past weekend was an interesting event. It is rare that the first significant frost event was so widespread over the state and also for a Freeze Warning to cover such a large portion of the country. The featured chart presents a histogram of the timing of the Freeze Warning product issued by NWS Des Moines. This recent event started at an abnormal time of 10 PM. This timing is a testament to how the cold temperatures were being driven by cold air advection into the state. Typically, the first events are driven by radiational cooling and as such are more isolated to the late overnight hours after a long period of cooling has happened overnight.

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