A spring heat wave stretched from the Midwest to the East Coast, toppling high temperature records in at least 21 cities. Thunderstorms accompanied by winds up to 70 m.p.h. rumbled across the Plains and tornadoes killed three persons in Texas. It was 83 degrees in Muskegon, Mich., setting a new record high for the second day in a row. The mercury climbed to 79 in Mansfield, Ohio, surpassing the 1973 record of 78. Fort Wayne, Ind., had 83, one degree above the 1952 record high.