What is the city’s longest period of continuous subzero temperatures?

Dear Tom,
I remember a January when temperatures did not get above zero day or night. What is the city’s longest period of continuous subzero temperatures?
— Frank W. Russell, Nalcrest, Fla.
Dear Frank,
The frigid spell that you remember was not in January, but over the Christmas holidays in 1983. The mercury dropped below zero at 7 a.m. Dec. 22 and remained there for 100 straight hours until 11 a.m. Dec. 26. During this prolonged frigid spell, the city not only recorded its coldest Christmas Eve, with a high of minus 11 and a low of minus 25, but also its coldest Christmas, with a high of minus 5 and a low of minus 17. Strong west winds sent windchills plunging to minus 80 and blowing snow created ground blizzards in open rural areas. December 1983 remains Chicago’s coldest December on record, averaging 14.3 degrees, a stunning 13.4 degrees below normal.