In the past 115 years, there have been 58 days when the national average temperature dropped below 18. Carbin said those occurrences often happen in periods that last several days so it makes more sense to talk about cold outbreaks instead of cold days. There have been 27 distinct cold snaps.

Between 1970 and 1989, a dozen such events occurred, but there were only two in the 1990s and then none until Monday.

“These types of events have actually become more infrequent than they were in the past,” said Carbin, who works at the Storm Prediction Center in Norman, Okla. “This is why there was such a big buzz because people have such short memories.”

Said Jeff Masters, meteorology director of the private firm Weather Underground: “It’s become a lot harder to get these extreme (cold) outbreaks in a planet that’s warming.”

And Monday’s breathtaking chill? It was merely the 55th coldest day — averaged for the continental United States — since 1900.