* WHAT...For the Heat Advisory, heat index values up to 108 expected. For the Extreme Heat Warning, dangerously hot conditions with heat index values up to 114 expected. * WHERE...Portions of central, east central, northern, northwest, and southeast Oklahoma. * WHEN...For the Heat Advisory, until 8 PM CDT this evening. For the Extreme Heat Warning, from noon to 8 PM CDT Tuesday. * IMPACTS...Heat related illnesses increase significantly during extreme heat and high humidity events. Hot temperatures and high humidity may cause heat illnesses.