What causes the Tule fog in the San Joaquin Valley?

The Tule fog is caused by the San Joaquin Valley's bowl-shaped geography trapping moisture, especially after rainfall and with calm winds.

How dangerous are pileups on Highway 99 during Tule fog?

Pileups on Highway 99 during Tule fog can be catastrophic, with historical incidents involving dozens of vehicles and multiple fatalities.

When is the next Tule fog expected in the San Joaquin Valley?

Fog is currently forecast in the San Joaquin Valley for at least the next week.

Home / Disasters and Accidents / Tule Fog Triggers Deadly Highway 99 Pileups

Tule Fog Triggers Deadly Highway 99 Pileups

20 Jan

•

Summary

Tule fog causes catastrophic conditions in San Joaquin Valley.
Highway 99 has seen numerous deadly pileups since the 1990s.
Recent crash involved 17 vehicles, resulting in one fatality.

Tule Fog Triggers Deadly Highway 99 Pileups

Dense Tule fog continues to plague the San Joaquin Valley, creating hazardous driving conditions, particularly on Highway 99. This meteorological phenomenon, unique to the region's geography, has a long history of causing deadly multi-vehicle collisions. Archive records show that since the 1990s, Highway 99 has been the site of numerous large pileups, some involving up to 90 vehicles.

The latest incident occurred on January 11, 2026, when 17 vehicles crashed on southbound Highway 99 near Fresno. Visibility was reduced to approximately a dozen feet, leading to the death of a 61-year-old driver. California Highway Patrol emphasizes that driver behavior, especially speeding in fog, is a critical factor in these tragic events.

Meteorologists explain that the Valley's bowl-like shape traps moisture, leading to persistent fog that can last for hours. Increased moisture from recent rainfall, combined with a lack of wind, exacerbates fog formation. Fog is expected to persist in the Valley for at least the next week, urging drivers to exercise extreme caution.