A Wind Chill Advisory is in effect for a good chunk of northern Iowa until 9 AM this Friday morning. The wind is also blowing snow around making for dangerous and variable driving conditions. The featured chart presents the time of day frequency of when Wind Chill Advisories are in effect as issued by NWS Des Moines. The overnight and especially early morning pre-dawn hours are certainly the favored time of day as that is typically when air temperatures are the coldest and it does not take much wind to drop wind chills into advisory thresholds when air temperatures are already below zero Fahrenheit. One quirk of the plot you may wonder about is the rapid changes in frequency every three hours. The reason is that NWS products are geared toward these hours of the day, so they are preferred starting and stopping hours for long fuse products like this advisory type.

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