Cold and warm air masses collided violently over the central plains, whipping up rain, hail and 60-m.p.h. winds that tossed small planes around like toys at the Kansas City Downtown Airport. About 25,000 customers of the Kansas City Power & Light Co. were left in the dark when high winds and lightning knocked down power lines. Power was also knocked out in Independence, Mo., where winds gusted to 65 m.p.h. While record low temperatures, dipping down to 39 and 40, were reported in parts of Wyoming and Montana, temperatures into the 90s continued to bake the East Coast.