with lester holt good evening americans feeling the heat tonight in ways and places they maybe never have where they live as high temperature records are expected to fall across much of the country. it is where we begin tonight. 38 million people across 20 states from california to the mississippi river right now living under heat alerts. record highs in the forecast today from cheyenne, wyoming where the forecast high is 99 to dallas/ft. worth airport which could reach 109. between now and wednesday nearly three dozen new record highs could be set the heat wave working its way to the east tonight, leaving the most vulnerable in its path at considerable risk experts are warning it is not summer as usual but rather another global gut check moment from a changing climate just as we face new obstacles in dealing with it. we ll get to that and the forecast from our team standing by in just a moment. let s start with miguel almaguer. reporter: shattering records and threatenin