* WHAT...Dangerously hot and humid conditions. Afternoon temperatures 104 to 116 degrees. Major Heat Risk. * WHERE...In Arizona, La Paz and Yuma counties. In California, Palo Verde Valley. * WHEN...Until 8 PM MST /8 PM PDT/ Sunday. * IMPACTS...Heat related illnesses increase significantly during extreme heat events. Overexposure can cause heat cramps and heat exhaustion to develop and, without intervention, can lead to heat stroke.