Late-May 1998 tornado outbreak and derecho

The Late May 1998 tornado outbreak and derecho was a weather event in the United States from May 30-31, 1998. It affected the northern half of the country and southern Ontario, from Montana to the Mid-Atlantic states.
Weather events.
Spencer, South Dakota tornado.
The first reports of severe weather were from Montana around 12:30 p.m. MDT. The tornado struck Spencer, South Dakota around 8:37 p.m. CDT. The Spencer tornado was an F4. Six people were killed in this tornado.
Derecho event (May 30-31).
The same storm that produced the Spencer, South Dakota tornado turned into a derecho affecting Minnesota, Wisconsin, Michigan, Ontario, and New York. The derecho killed another 6 people.
New York and Pennyslvania tornadoes (May 31).
On May 31, tornadoes broke out across Pennyslvania and New York, this being the most destructive to sweep across the two states since the 1985 United States-Canada tornado outbreak.