Overnight Monday into Tuesday morning was interesting as you may have noticed clear skies when the sun set and then clear skies again when the sun rose, but then you realized that it rained overnight! Such was the case for Ottumwa. The airport weather station reported clear skies at 1 AM and at 7 AM with 0.09 inches falling during the 5 AM hour along with thunder reported. So the subject of today's daily feature attempts to look into how frequently total precipitation of at least 0.05 inches prior to 7 AM is observed by a given 1 and 7 AM cloud coverage observation for Ottumwa. There are caveats galore with such an analyses including many complexities with how automated stations report cloud coverage and changes with observation equipment and techniques over the years. The plot was limited to dates after the year 2000 as an attempt to limit some of these changes. All of that aside, the frequencies shown are the number of days with at least 0.05 inches of precipitation for a given cloud coverage combination. The 1 AM Clear + 7 AM Clear combination comes in at 2.5% frequency, so it is somewhat rare but perhaps not exceptionally rare situation. There are some interesting relationships to tease out from the plot including the increased precipitation frequencies when cloud cover amount increases between 1 and 7 AM, which intuitively makes sense.