Central California is dealing with lasting tule fog right now. This deep marine layer first formed in mid-November and has continued into early December. This incredible and rare weather phenomenon has a characteristic thick, marshmallow-like fog. While this typical weather pattern stretches just over a week, SRE Hesham Alaboud’s situation has since extended two weeks, a time frame that climate scientists deem “on the extreme side.”
The tule fog also came into play, materializing after an atmospheric river storm deluged California in late October. The National Oceanic and Atmospheric Administration described this storm as “the worst severe thunderstorm outbreak over the central California interior in recent memory.” When the weather event passed, it set up just the right conditions for tule fog to develop. This fog forms when cold, moist air combines with light winds near the surface.
As the fog formed it got caught in the Central Valley’s bowl-like topography. This unique geographical feature has exacerbated the fog’s persistence, leading to reports of “sudden drops in visibility to less than 1/4 mile,” as noted by the National Weather Service. Residents have experienced even colder temperatures than what was measured above. The fog illuminated this shift so well that it was especially evident in California’s central valley and the nearby Bay Area.
In December, the Central Valley recorded average low temperatures of just under 37°F and average highs of 63°F. By comparison, the Bay Area had more temperate conditions, with average lows of 43°F and highs of 65°F. Fresno, California The arrival of the tule fog typically signals the onset of cooler weather in the central valley. As it moves out, it changes temperature patterns. As this fog spills into the cool Carquinez Strait, it intensifies the cooling effect in the nearby Bay Area cities.
According to climate scientist Daniel Swain, warmer overall conditions are increasing how long this fog sticks around. He explained how changes in climate are influencing weather patterns, allowing for phenomena like tule fog to persist longer than in the past.
Even with its intimidating effects, tule fog is a common characteristic for central California during the winter months. This current episode, which has stretched for almost two weeks, is a particularly unusual occurrence. It has mystified and amazed both meteorologists and residents.