Some warmer air aloft above the shallow sub-freezing air at the surface cold lead to some freezing rain in the early morning hours on Saturday. If you’re driving to Boulder from elsewhere in NE Colorado you might want to allow some additional time to get to the stadium, though I image CoDOT will treat the Interstates. Mignt be another factor limiting attendance at Folsom Field. GO UTES!!
when I lived in CO 32 years ago, they treated the interstate with pea-gravel. I think they tried passing it off as sand, but it really messed up my car’s paint. Not a lick of salt to melt the ice, but gravelly sand.
they may have changed in the intervening decades, but I don’t know.
When I lived in the area some places, including Ft Collins, were using some sort of ash which made for lots of dirty snow and cars. Boulder was mostly relying on the “solar plow”; sand in the intersections.
There really isn’t warm air aloft. This is more a case of no ice crystals being present in the layer of air near the surface, so the fog might precipitate out as freezing drizzle.