The extreme heat in the central and southern US could make outdoor activities uncomfortable and potentially hazardous, especially with heat indices reaching triple digits in the Deep South and Southern Plains. Rain and thunderstorms in the East and Southeast may disrupt outdoor plans, particularly on Sunday, which is expected to be the wettest day. The risk of flash flooding and lightning could also pose safety concerns in these areas. Cooler temperatures in the Northwest may provide some relief but could affect those unprepared for the chill.