Dear Tom, 
Last December 23rd, the high temperature for the day failed to reach zero. How many days, before Christmas, in Chicago weather history have recorded subzero high temperatures?

Kent Rhodes  Lisle

Dear Kent,

The city’s high of minus one last December 23 was, indeed, a rare event. Checking the city’s climate archives dating back to late 1870, Chicago has recorded only seven such days, in the fledgling cold season, with a subzero high on or before December 25. Those other six occurrences: minus 2 on December 20, 1871, minus 2 on December 28, 1880, minus 2 on December 15, 1901, and in 1983, minus 6 on December 23, minus 11 on December 24, and minus 5 on December 25.