Home / Weather / California Valley Swallowed by Giant Fog
California Valley Swallowed by Giant Fog
29 Nov, 2025
Summary
- Nearly 400-mile-long Tule fog reappeared daily for a week.
- Fog forms from radiation cooling and moisture trapped by inversions.
- Dense fog advisories warn of high transportation risks across valley routes.
California's Central Valley is currently experiencing a persistent and extensive fog bank, nicknamed Tule fog, which has been a daily occurrence for the past week. This phenomenon stretches nearly 400 miles, engulfing the entire valley from Bakersfield to north of Sacramento. The fog is a type of radiation fog, forming when heat radiates away at night, causing temperatures to drop to the dew point and moisture to condense.
The fog's persistence is amplified by a temperature inversion, where a layer of warmer air above traps the cold, dense fog and pollutants near the ground. This atmospheric condition, combined with lingering moisture from recent heavy rains, has created a stable environment for the fog to form nightly. Unless dry air or prolonged sunshine intervenes, the fog is expected to remain.
The National Weather Service has issued widespread dense fog advisories, highlighting a "high transportation risk" on numerous interstates and state routes within the valley. Drivers are urged to exercise extreme caution, reduce speed, and maintain safe following distances due to severely limited visibility.
