As people across the Metro headed back to work Tuesday morning after the holiday weekend, accidents quickly started popping up due to icy conditions. But it hadn't snowed, there was no freezing drizzle, and it certainly wasn't raining. What happened?
With the dew point considerably colder than the air temperature, fog was not exactly expected overnight. However, conditions reported at Eppley included a mix of patchy fog, fog/mist, and freezing fog just before 10 p.m. Monday through about 3 a.m. Tuesday. Freezing fog is a known culprit in the formation of black ice on roads, which is very difficult to see.
A temperature inversion in the atmosphere also likely played a part in the icy conditions. While the atmosphere usually cools with height, a layer of warmer air above the colder surface causes a temperature inversion. This can lead to what is called "radiation frost" which can stick to roads.
These conditions together made for a messy morning commute.