This past weekend, the San Joaquin Valley experienced exceptionally thick fog, marking one of the most severe occurrences in years. Over a stretch of 10 hours on Friday morning, Fresno-Yosemite International Airport reported visibility dropping to just 1/16th of a mile. Notably, such low visibility had not been recorded for that long in 15 years.
Record Low Visibility in Fresno
The fog conditions persisted through Saturday evening and into Sunday, where the airport measured 20 consecutive hours of visibility at only 1/8th of a mile. This level of fog had not been seen since January 1962, a staggering 64 years ago.
Contributing Weather Conditions
- Heavy rain at the start of the rain season
- Ground saturation and standing water
- High-pressure systems forcing the jet stream north
- Clear nights leading to temperature drops and increased humidity
These unique weather elements have combined to create ideal conditions for the formation of fog. The early rain soaked the ground, while subsequent clear skies allowed temperatures to fall close to the dew point, resulting in 100% relative humidity. This moisture condenses, forming the dense fog covering the valley.
The Valley’s Fog Dynamics
Geographically, the San Joaquin Valley is surrounded by mountains, which limits airflow and traps moisture. The lack of wind exacerbates the fog situation, allowing for a repetitive weather cycle. Until a major storm breaks this cycle, the fog is expected to persist.
Forecasts suggest that the next significant weather change may not occur until late January. Residents are left wondering if the fog will continue in its current dense form, or if it may transform into a colder, cloudier gloom reminiscent of earlier December conditions.
Future Outlook on Fog Conditions
The heart of the fog season typically runs from Veterans Day to Valentine’s Day. While fog can still occur into February and March, it generally diminishes as spring approaches. The recent weather has shown that when afternoon sunshine breaks through, conditions can lead to warmer, fog-free days. Conversely, persistent cloud cover may trigger prolonged fog scenarios.
As the region anticipates what lies ahead, understanding these patterns is crucial for residents navigating the current and future fog events. With each passing week, the dynamics of San Joaquin Valley’s fog will continue to unfold.
