* WHAT...For the Dense Fog Advisory, visibility one quarter mile or less in dense fog. For the Heat Advisory, heat index values near or exceeding 105 expected. For the Extreme Heat Warning, dangerously hot conditions with heat index values up to 112 expected. For the Extreme Heat Watch, dangerously hot conditions with heat index values up to 110 possible. * WHERE...Portions of central, south central and southwest Iowa. * WHEN...For the Dense Fog Advisory, until 9 AM CDT this morning. For the Heat Advisory, from noon today to noon CDT Sunday. For the Extreme Heat Warning, from noon to 9 PM CDT Sunday. For the Extreme Heat Watch, from Sunday evening through Monday evening. * IMPACTS...Heat related illnesses increase significantly during extreme heat and high humidity events. Hot temperatures and high humidity may cause heat illnesses. Low visibility could make driving conditions hazardous. Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. If driving, slow down, use your headlights, and leave plenty of distance ahead of you.