The fog was remarkably thick over some parts of Iowa on Thursday prompting the NWS to issue a Dense Fog Advisory. The featured chart presents the combination of selected Iowa airport weather station observations of visibility (dots) with crosses overlain for those reports whilst under a Dense Fog Advisory for that location. The initial issuance needed to be extended in time and space as the fog spread and was stubborn to burn off during the morning hours. While Cedar Rapids did dip to low visibility around 9 AM, its duration was short lived and thus not warranting a NWS headline. You can see during the later morning hours as the fog lifted / burned off, the lifting of the Dense Fog Advisories as well.

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