An extreme heat warning will take effect at 10 a.m. Thursday for the San Diego County mountains, including Julian and Pine Valley, and the county deserts, including Borrego Springs. Forecasters expect highs ranging from the mid-90s to 105 degrees in the mountains and 115 to 120 degrees in the deserts through 8 p.m. Sunday.
The warning expands to the San Diego County valleys at 10 a.m. Friday and remains in effect through 8 p.m. Sunday. High temperatures are forecast to reach the mid-90s in the western valleys and climb to around 105 degrees near the foothills, affecting communities including El Cajon, Escondido, La Mesa, Poway, San Marcos and Santee.