Meteorological Synopsis
Early on May 15, 1998, a stationary front was positioned from the western border of Minnesota, southward to Kansas. To the east of the stationary front, temperatures and dew points were unseasonably high. Several Minnesota cities reported record high dew points (including the Twin Cities of 70 °F (21 °C)) and low–minimum temperates for May 15. A deepening area of low pressure over Kansas ejected to the north, moving along the stationary front. Behind the low pressure area was much cooler and drier air. The clash of these two differing air masses was the impetus for the development of the severe weather.
A squall line moving at speeds to 70 miles per hour (113 km/h) with embedded supercells entered Minnesota from the southwest during the early afternoon hours, and raced northward across most of the state. The primary threat from these storm was large hail, which was enhanced by the strong downburst winds. In addition to the hail and high winds, five tornadoes also touched down with the supercells, killing one person.
Read more about this topic: May 15, 1998 Minnesota Storms