CLARKSVILLE, TN (CLARKSVILLE NOW) – With a high of 96 degrees and a heat index up to 107 expected today, the National Weather Service has issued a Heat Advisory. The advisory is in effect through 7 p.m. “Hot temperatures and high humidity may cause heat illnesses,” the NWS said. “Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors.”