Info from The Longmont Times-Call local paper, with some editing:
The high temperature (Wed) was 51F, around 1 p.m.
3:55 p.m.: according to records at Vance Brand Municipal Airport, (KLMO) it was a seasonal 42F.
~4 p.m.: the Arctic front hit.
4:15 p.m.: the temperature at the airport was 28F...