With commentary . This is for DCA since the station began there and does not include Dec 1989 which was even greater below normal due to time of year but not as bitter cold daily temps
Gold-1994 with an incredible-140 for 7 days 1/15-1/21
Silver- 2026 with a -121 1/24-1/30
Bronze-1982 with -117 and a 10 day of -178 and a one day -33 departure 1:11-1/17
4th-1977 at -108 but only 3 days were at or above normal that month with 0,1,2 as the + departures. Fell below freezing every day of the month
im looking at a few more but these well may be the toppers