A vocabulary of landscape — a landscape of words
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tule fog
Tule fog is the dense ground fog that forms in California’s Central Valley in winter, sitting in the basin for days at a time with visibility down to a few yards. It forms after rain, on long clear nights, when the ground radiates its heat away and the moist air just above it cools below the dew point, and an inversion traps the whole thing under warm air with no wind to move it.
Etymology
The name is for the tule, the bulrush that grows in the valley’s marshes, and the word came into Spanish from Nahuatl, the Aztec language, and into English from Spanish. The phrase out in the tules means the middle of nowhere, from the same source.
Notes
It is a seasonal fixture rather than an event, and the valley’s highways carry warning systems. The fog also matters agriculturally: Fruit and nut trees need a certain number of cold hours to set a crop, and the overcast keeps daytime temperatures down, so the same weather that closes roads is what allows the orchards to work.