Mean: 336 or December 2
Median: 337 or December 3
Standard Deviation: 18.471534
Earliest: October 20, 1989
Latest: January 5, 1987

Sometimes, Houston see its first 32°F in January, like in the winter of 1970-1, 1986-7, and 1994-5.
Interesting to note the earliest 32°F at KIAH was 4 days after Hurricane Jerry made landfall.