The strong storms that developed early Thursday evening over Iowa were a bit of a forecast surprise with only very late runs of various forecast models depicting a possible robust environment to produce elevated thunderstorms capable of large hail. The NWS issued a number of warnings for the event and got hail reports to verify those warnings. The featured chart looks into the time of day frequency of having Severe Thunderstorm Warnings during the month of October. The chart presents the time of day frequency for Des Moines with the overall frequency plotted in tan and the values for October in blue. Of course, there are much fewer events during October so the plot gets a bit noisy vs the smooth full year values. Having such warnings during the night time is certainly more common than during the day as processes like the nocturnal "Low Level Jet" help fuel thunderstorms overnight.