* WHAT...Dangerously hot conditions. Afternoon temperatures 100 to 113. Major Heat Risk. * WHERE...Chuckwalla Mountains, Chiriaco Summit, Joshua Tree NP East, and Joshua Tree NP West. * WHEN...Until 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.