Overview

• A deep marine layer and offshore low pressure have kept early-week highs 5–10°F below seasonal norms in coastal and inland valleys.
• A high-pressure ridge building Wednesday will drive a temperature surge into the upper 90s and low triple digits through Thursday.
• Heat advisories and Impact Days cover interior valleys, the Inland Empire and desert regions with fire risk elevated but limited by light winds.
• Desert communities near Borrego Springs could peak at 115–119°F while Bay Area inland pockets such as Livermore edge toward 100°F.
• Onshore breezes are forecast to return by Friday as the ridge weakens, restoring coastal stratus and easing inland heat.