Since 1900 the average high/low on the coldest day of each winter has been 19°/6° (in the last third of the 18th century it was 14°/2°; in the 21st century it's risen to a relatively temperate 20°/9°). The coldest day has occurred as early as Nov. 30 (winter of 1875-76) and as late as March 15 (winter of 1931-32). Nearly half of the coldest days of New York's winters have occurred in the four-week period between Jan. 9 and Feb. 6. For this analysis "coldest day" is based on daily mean temperature (average of high/low), not just the low temperature.
THE SPECTRUM OF THE BIG CHILL
The dates of the most frigid coldest winter day and the mildest coldest winter day are, in their respective years, one day apart. The coldest of them all fell on Dec. 30, 1917, when the high/low was 2°/-13°. At the other end of the spectrum, the mildest reading to have the distinction of being the coldest day of a winter was 31°/20° in the winter of 2001-02 on Dec. 31, 2001. January 18 is the date to see the most coldest days of winter - six. Three dates in February have been the coldest for five winters each: Feb. 2, Feb. 5 and Feb. 17.
TWO MEASURES OF "COLDEST"
Although the coldest day is usually the same date as the coldest temperature, they have occasionally occurred on different dates (on average, in one out of four winters). For instance, although the coldest reading of all time is -15°, the coldest day of all time, based on mean temperature, had a low of -13°. Although this is two degrees "warmer" than the coldest reading, the day's high of 2° was six degrees colder than the high on Feb. 9, 1934, so it ended up with a mean of -5.5° compared to a -3.5° in 1934. (The most recent instance was the winter of 2019-20 as its coldest day was on Dec. 19, with a high/low of 25°/16°, while the coldest reading was 14° on 2/15.)
A number of consecutive years, or a few years apart, have had their coldest day on practically the same date. And in one interesting case the coldest day of winters one hundred years apart (1916 and 2016) occurred on the same date - Feb. 15. And the coldest day of the winters of 1884 and 1984 were two days apart, on 12/23 and 12/25, respectively.
The coldest day of some winters has fallen on a holiday. The one exception is Christmas Eve day.
"COLDEST COLDEST, MEET MILDEST COLDEST!"
Of course, the coldest winters have a lot of very cold days that that would easily qualify as the coldest dates of many of the winters with average or above average temperatures.
SOMETIMES IT SNOWS
Snow falls very infrequently on the coldest day of the winter - just six winters have had an inch or more of snow on this day. However, a few were significant, with the stand out being the 12.5" accumulation on the coldest day of the winter of 1966-67 (Feb. 9, which had a high/low of 16°/7°).
Finally, the coldest day of the winter of 1963-64 was preceded by a snowstorm that dumped 11.5" the day before, while three storms that followed the coldest day of winter by one day dumped more than ten inches. The storm in February in 2003 dumped 16.3", but started on the coldest day of the winter, with 3.5" falling that evening.