2012: The National Centers for Environmental Prediction in the United States replaced the Rapid Update Cycle (RUC) weather prediction model with the Rapid Refresh (RAP) model.
1982: The Weather Channel went on the air in the United States.
2000: The GOES 11 weather satellite was launched. Part of the Geostationary Operational Environmental Satellite program, GOES 11 was used as a backup satellite until it replaced the GOES 10 in 2006, and would provide weather forecasting data mainly for the Western United States and Pacific Ocean from 2006 until its retirement in 2011.
2007: A three-day tornado outbreak featuring more than 100 tornadoes began across a large area of the Central United States. One tornado destroyed 95% of the town of Greensburg, Kansas, and was the first tornado ever rated EF5.
1995: A major hailstorm caused around $1 billion in damage in the Dallas–Fort Worth metroplex. This was the costliest hailstorm in United States history.
1965: A series of violent tornadoes affected the Twin Cities area of Minnesota.
1981: Tropical Storm Arlene moved across Cuba. Minimal damage was reported.
1995: More than 20 inches (510 mm) of rain in just 12 hours caused major flooding in southern Louisiana, causing more than $1 billion in damage.
1990: A severe tropical cyclone made landfall in the Andhra Pradesh state of India, killing nearly 1,000 people.
1933: A tornado killed almost every resident of the small town of Beatty Swamps, Tennessee. Because of the destruction, the town was abandoned permanently.
1953: An F5 tornado destroyed areas of downtown Waco, Texas, killing 114 people.
1948: A Douglas DC-4 crashed while flying into a thunderstorm near Libenge, Congo, killing 31 of the 32 aboard.
1998: The NOAA-15 weather satellite was launched into a polar orbit from Vandenberg Air Force Base, California. Originally planned for just a 5 year mission, as of early 2020 the satellite was still returning useful atmospheric and space data from several instruments.
2007: Cyclone Akash made landfall in Bangladesh, causing almost $1 billion in damage.
1966: The Nimbus 2 weather satellite was launched. It collected information about atmospheric temperature and cloud cover until early 1969.
1986: Severe flooding from an ice jam completely destroyed the town of Winisk, Ontario, which was subsequently abandoned. Two people were killed.
2001: A Yakovlev Yak-40 aircraft crashed while flying through a thunderstorm near Sari, Iran, killing 30 people, including several members of the Islamic Consultative Assembly and other government officials.
1902: A tornado killed 114 in Goliad, Texas.
2018: Cyclone Sagar struck northwestern Somalia, killing 56 people in three countries. It was the strongest tropical cyclone on record to strike Somalia.
1916: A tornado struck the town of Codell, Kansas. Incredibly, the same town would be hit by two more tornadoes on May 20, 1917 and May 20, 1918.
1976: Typhoon Pamela passed over the island of Guam, damaging or destroying 80% of the island's buildings but only killing one person.
1951: Hurricane Able, the strongest off-season Atlantic hurricane ever recorded, reached its peak strength of 115 miles per hour (185 km/h) off the coast of Cape Hatteras.
1917: Edward Lorenz, meteorologist and original founder of the field of chaos theory, was born in West Hartford, Connecticut.
1988: TACA Flight 110 lost power to both its engines due to water ingestion after flying through a heavy thunderstorm. Unable to reach an airport, its pilots made a successful deadstick landing on a grass levee near NASA's Michoud Assembly Facility.
2009: Cyclone Aila struck Bangladesh, killing more than 300 people.
1917: At one point thought to be the longest single tornado track on record, a family of several tornadoes killed over 100 people in Illinois and Indiana.
2018: For the second time in two years record flooding struck Ellicott City, Maryland.
1941: After searching for several hours, the German weather ship Sachsenwald recovered two survivors from the sinking of the battleship Bismarck
2010: Tropical Storm Agatha made landfall near the Guatemala–Mexico border, killing more than 200 people due to flooding, landslides, and a sinkhole.
1998: After a supercell spawned an F4 tornado that nearly wiped out the town of Spencer, South Dakota, the storms organized into a destructive derecho that tracked over 1,000 miles (1,609 km) across the southern Great Lakes region of the United States and Canada.
1953: Tropical Storm Alice moved over the western tip of Cuba.