Dense fog advisories are active across wide swaths of the United States this week, from California's valleys to the Pacific Northwest and Middle Tennessee. San Francisco Bay Shoreline and East Bay Interior Valleys were placed under a dense fog advisory by the National Weather Service on Sunday at 5:58 a.m., with the advisory in effect until 9 a.m. Multiple regions are reporting similar conditions as moisture settles in overnight.
When a dense fog advisory is issued, it means widespread dense fog has developed and visibility often drops to just a quarter-mile or less. This isn't just inconvenient—low visibility could make driving conditions hazardous. If you're commuting during early morning or evening hours when fog typically thickens, expect sudden changes in sight lines and adjust your speed accordingly. If driving, slow down, use your headlights, and leave plenty of distance ahead of you. Patchy dense fog will result in sudden changes in visibility.
If visibility drops to near-zero while you're driving, the safest move isn't to keep going slowly. In extremely dense fog where visibility is near zero, the best course of action is to first turn on your hazard lights, then simply pull into a safe location such as a parking lot of a local business, and stop. Once stationary, turn off all lights except the hazard flashers, engage the emergency brake, and release the brake pedal to ensure your tail lights are not illuminated, reducing the risk of other drivers colliding with your stationary vehicle. The goal is to get completely off the roadway so other drivers see your hazards but don't mistake your tail lights for a vehicle still in motion.