January 1977 was the coldest month in modern Philadelphia climate record, averaging over a dozen degrees colder than our current normals and averaging just 20 degrees for high/low blend throughout the month. Compared to the relatively mild January we've had, January 1977 would definitely be a shock to our system. It is the true gold standard of cold months though in Philadelphia and one that arguably will be tough to reach again.
The "warm" day of January '77 was January 28th -- a high of 43 degrees in Philadelphia and Atlantic City. The day was also marked by a passage of a strong cold front during the early evening hours. Philadelphia's had its share of strong cold fronts in the past that dropped temperatures 15, 20 degrees in an hour; however, this front also brought potent winds along with a period of snow, resulting in a short duration blizzard in the Delaware Valley.
The wake of the cold front resulted in intense winds, gusting to 56 mph in Atlantic City, 52 mph in Philadelphia, 58 mph in Reading, and 67 mph in Allentown. Temperature drops of fifteen to as much as 26 degrees accompanied the front as it passed through within an hour's time. This storm was more notorious to Buffalo and Upstate New York as the Blizzard of '77 -- bringing a foot of new snow along with multiple feet of wind swept snow off of frozen Lake Erie. Locally, the system didn't bring much much in the way of snow -- accumulations were trace to a couple of inches with the squall front as it blew through the region. However, the impact of the storm was a several day duration of arctic chill and strong winds -- the high on the 29th in Philadelphia was just 18 degrees and it taking until February 2nd before the high temperature got back above freezing.