Nearly 40% of Decembers since 1869, or 59, have experienced cold snaps/cold waves that lasted five days or longer (about half were seven+ days). The most recent occurred in 2017. In addition to the five-days+ qualifier, a cold snap needed to have an average high temperature of 32° or colder to be part of this analysis. The longest of them lasted 15 days, in 1876; six have had sub-zero readings; six had twelve inches of of snow or more; and six had no snow whatsoever (not even a trace). Finally, six Decembers had two periods of Arctic cold.
The coldest December cold wave occurred in 1917, when the six days between Dec. 26-31 had an average high/low of 17°/2°. Most recently, the last six days of Dec. 2017 had an average high/low of 23°/15°, which tied for ninth coldest.
Fifteen Decembers have had cold waves lasting ten or more days. The lengthiest was 16 days in Dec. 1904 (average high of 32°/22°), followed by a 15-day stretch in 1876 (27°/17°). The coldest of these lengthy cold waves was one of 10 days in 1872 (24°/10°).
TWO IN ONE MONTH!
Six Decembers had two significant cold snaps. The last time it happened was in 1955, with one of five days and the other lasting six days (they were three days apart). The two in 1917 covered 15 days (eight days apart).
COLD SNAPS MORE PREVALENT 100+ YEARS AGO
The greatest concentration of Decembers with cold waves was between 1876 and 1904, when 20 of the 29 Decembers had at least one cold snap. The most consecutive Decembers to have a cold snap is four, which has happened four times: in 1901-1904, 1914-1917, 1932-35 and 1942-45; there have also been four three-year streaks, with the most recent being 1958-1960. The most consecutive years without a cold snap is eight, and it's happened twice, in 1981-1988 and 2001-2008. And there was a seven-year hiatus from 2010 to 2016.
SNOWIEST & LEAST SNOWY
Six cold snaps received more than 13 inches of snow. The most was 22.5" in 1883, and 21.5" in 1872. The most recent was in 2000 when 13.3" fell. Five of the Decembers had snowstorms that dumped a foot or more, with the most being 18.0" on Dec. 26, 1872. And although December 1942, with 6.0", isn't found on the "most snowy" list below, it's worth mentioning because it had measurable snow fall on six of the cold wave's ten days.
At the other end of the snow spectrum, ten December cold snaps had no measurable snow. Eight of them were five or six days in duration, but December 1870 and December 1989 lasted 11 and 10 days, respectively.
BELOW- ZERO READINGS
Seven of the Decembers had at least one sub-zero low. The most recent was in 1980 (on Christmas Day). These cold waves accounted for all of the twelve sub-zero lows that have been reported in December. And although December 1872 had no below-zero readings, it had the distinction of having six days in a row with lows in the single digits (ranging from 4° to 8°). At the other end of the spectrum, the coldest temperature of five December cold snaps was a relatively mild 18° or 19° (most recently in 1970).