* WHAT. High temperatures of 88 to 100 in the mountains and foothills. Low temperatures in the mid 60s into the 70s. * WHERE. San Diego County Mountains. * WHEN. Until 8 PM PDT Monday. * IMPACTS. Hot temperatures may cause heat illnesses. * ADDITIONAL DETAILS. Moderate HeatRisk can be dangerous for outdoor activities.

* WHAT. Dangerously hot conditions with high temperatures of 108 to 113. Low temperatures in the upper 70s and 80s. Slight cooling is expected on Tuesday into the latter part of the week. * WHERE. Coachella Valley and San Diego County Deserts. * WHEN. Until 8 PM PDT Monday. * IMPACTS. Heat related illnesses increase significantly during extreme heat events. Warm overnight temperatures will lead to less relief from the heat, prolonging impacts. * ADDITIONAL DETAILS. Major HeatRisk from excessive temperatures.