* WHAT...Dangerously hot and humid conditions. Afternoon temperatures 105 to 115 degrees. Moderate to Major Heat Risk. * WHERE...In Arizona, Parker Valley and Yuma. In California, Imperial Valley. * WHEN...Until 8 PM MST /8 PM PDT/ Thursday. * 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.