* WHAT...Temperatures 90 to 98 for Inland Orange County, 90 to 102 for the San Diego County Valleys, 100 to 107 for the Inland Empire and 89 to 100 in the mountains. Temperatures increase slightly for the middle and end of next week, making for a prolonged and dangerous stretch of heat. * WHERE...Orange County Inland Areas, Riverside County Mountains, San Bernardino and Riverside County Valleys-The Inland Empire, San Diego County Mountains, San Diego County Valleys, and Santa Ana Mountains and Foothills. * WHEN...For the Heat Advisory, until 10 AM PDT Tuesday. For the Extreme Heat Watch, from Tuesday morning through Friday evening. * IMPACTS...Heat related illnesses increase significantly during extreme heat events. Hot temperatures may cause heat illnesses. * ADDITIONAL DETAILS...Low temperatures 5 to 10 degrees above normal will limit relief from the heat. Increasing temperatures into the middle of next week will increase the threat of heat-related illness across populations.