In Minnesota, we always talked about the two levels of freezes. The official one at 32, and then the "killing" freeze in the mid-20s. My low so far this season has been 29.7. There is stuff still quite alive in my yard.
Big variation with calm winds this morning. Manassas made the teens, IAD low 20s, most of the DC beltway area in the mid-20s, my hill was 30, DCA 31, and DC downtown in the low 30s.
It is pretty easy. Last night the winds stayed up and kept the atmosphere more mixed. Therefore there was a more homogeneous temperature distribution. On the 20th, it was whisper calm, and that is where the river and heat island take over. The river on the 20th was still 47 degrees at little falls.
Andrews was 31. H2O in Alex was 31. I was 30. I don’t know what you are talking about. We know exactly where the thermometer is, in the middle of a grassy area on the river side of the runways.
The story, as I understand it, is that someone bought the original Eastern server. He had it for a while and kept it active. But he passed away at some point. I think Ian and others know the full study.