* WHAT...For the Heat Advisory, heat index values up to 109 expected. For the Extreme Heat Watch, dangerously hot conditions with heat index values up to 113 possible. * WHERE...Portions of northwest and west central Arkansas and east central, northeast, and southeast Oklahoma. * WHEN...For the Heat Advisory, from 1 PM to 8 PM CDT Monday. For the Extreme Heat Watch, from Tuesday afternoon through Tuesday evening. * IMPACTS...Heat related illnesses increase significantly during extreme heat and high humidity events. Heat related illnesses are possible especially impacting those not acclimated to the conditions or those performing strenuous activities.