...HEAT ADVISORY IN EFFECT UNTIL 8 PM EDT THIS EVENING... * WHAT...Heat index values around 105 expected. * WHERE...Portions of central, north central, and northern Maryland and northern Virginia. * WHEN...Until 8 PM EDT this evening. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses. PRECAUTIONARY/PREPAREDNESS ACTIONS... Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. By THe National Weather Service, Sterling, Va.