Wed Dec 17 13:40:00 UTC 2025: News Article Summary

California’s Central Valley Engulfed in Weeks-Long Tule Fog Event

Central Valley, CA – For over two weeks in late November and early December 2025, California’s Central Valley was blanketed by a persistent, sprawling tule fog, an atmospheric phenomenon visible even from space. The fog, stretching across 400 miles from Redding to Bakersfield, was captured in stunning detail by NASA’s Terra satellite and NOAA’s weather satellites.

Tule fog, named for the tule sedge that grows in the region’s marshes, is a radiation fog that typically forms in the Central Valley during colder months when conditions are calm, and the soil is moist. This year, exceptionally wet conditions throughout autumn, coupled with a high-pressure system that acted as a “lid,” trapping moisture, created the perfect environment for prolonged fog formation.

While the fog remained mostly confined to the valley by the Coastal Range and Sierra Nevada mountains, it occasionally pushed through the Carquinez Strait toward San Francisco Bay. The fog layer also brought cooler temperatures to the valley, contrasting sharply with the warmer-than-normal conditions in the rest of the state. However, scientists note that the overall air mass was warmer than in previous tule fog events, possibly due to warm ocean temperatures and a low Sierra Nevada snowpack. This might explain why the fog sometimes formed at a higher altitude, resembling stratus clouds, rather than a dense ground-level fog.

While such prolonged fog events have occurred in the past (e.g. Fresno saw 16 consecutive days in 1985), research suggests that tule fog has been occurring less frequently in recent decades. Despite the challenges it poses to transportation, tule fog is actually beneficial for the valley’s fruit and nut trees, providing the necessary chilling hours and protection from direct sunlight needed for dormancy and future productivity.

NASA’s Earth Observatory continues to monitor the event, using satellite data to study its impact on the region and provide insights into the complex atmospheric conditions that contribute to its formation.

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