Today's WaPo includes a graphic representation of presidential inauguration weather (click to enlarge):
Weather doesn't follow a 4-year cycle, so here are CapitalClimate charts of the detailed January 20 Washington, DC, temperature and precipitation records since 1933:
Note the large temperature range, from a high of 70° in 1951 (not an inauguration year) to a low of -2° for Reagan's second inaugural in 1985, the coldest inauguration in history. The long-term averages of 42° for a maximum and 27° for a minimum are equal to the coldest of the year in Washington.
The record precipitation for the date of 1.77" fell in 1937. An inch or more also occurred in 1979 and 1988, with 1995 close behind at 0.99". In all, 39 out of the last 78 years since 1930, or exactly 50%, have had at least a trace of precipitation on January 20.
The maximum snowfall on the date was 3.8" in 1975, although 7" fell the day before Kennedy's inauguration in 1961. At least a trace of snow fell in 23 years, or just under 30% of the time. Of those, 17 had measurable amounts, and 1" or more was observed 9 times. The maximum amount of snow on the ground was the 8" in 1961. There has been a trace or more of snow on the ground in 25 of the years since 1930, and 19 of those had at least an inch.
So, the bottom line of inauguration weather history is: If you're planning to attend the events, particularly those outdoors, be prepared with a variety of clothing and footwear.
Other references on inauguration weather history:
Global Day of Overshoot
3 months ago