1894: A record late snow of two to eight inches whitened parts of central and eastern Kentucky. Lexington received six inches of snow, and Springfield Kentucky received 5 inches.
1916: In three consecutive years, a tornado passed near or through the town of Codell, Kansas. The tornado on this day was an estimated F2. The estimated F3 tornado in 1917 moved two miles west of town. Finally, an estimated F4 tornado moved through Codell on May 20th, 1918. This tornado killed 9 and injured at least 65 others.
Source: The Weather Doctor.
1957: A tornado touched down to the southwest of Kansas City and traveled a distance of seventy-one miles cutting a swath of near destruction through the southeastern suburbs of Ruskin Heights and Hickman Mills. The tornado claimed the lives of forty-five persons and left hundreds homeless. It was the worst weather disaster on record for Kansas City. About all that remained of one house were a small table and a fishbowl atop, with the fish still swimming about inside the bowl. A canceled check from Hickman Hills was found in Ottumwa, Iowa, 165 miles away. Pilots reported debris at an altitude of 30,000 feet.
Source: NWS Office in Kansas City.
1983: A bow echo passed through the Houston area during the early morning hours on May 20th. The storm system caused 11 fatalities. The bow echo produced four downburst swaths and eight tornadoes.
2013: Several supercell thunderstorms developed during the early afternoon of May 20th along with a dry line in central Oklahoma. One of these storms developed near Chickasha and rapidly intensified, producing a tornado which touched down at 2:56 PM CDT on the west side of Newcastle. The tornado became violent within minutes, then tracked east-northeastward across the city of Moore and parts of south Oklahoma City for about 40 minutes before finally dissipating near Lake Stanley Draper. The tornado caused catastrophic damage in these areas and was given a maximum rating of EF-5. The tornado claimed 24 lives, injured scores of people, and caused billions of dollars in damage.
— NWS Seattle (@NWSSeattle) May 21, 2017