One of the most frequently issued National Weather Service headlines is the ever exciting Dense Fog Advisory. A number of such advisories have been issued over Iowa this week as a cooler air mass has interacted with late summer elevated humidity. The featured chart looks into the frequency of such advisories issued by NWS Des Moines by time of day. The chart presents the summer season (June, July, August) frequency along with the overall full year frequency. The difference between the two is quite informative. During the summer season, solar inputs are very strong and will work to "burn off" the fog pretty much every day. Of course, there is no "burning" process, but a process of heating the ground, heating the lower atmosphere and reducing relative humidity levels. Such is the case again this Friday with morning fog and a number of advisories currently active.