https://www.mercurynews.com/2019/04/10/who-killed-the-tule-fog-uc-berkeley-cracks-the-case/

Scientists have cracked the cold case of the Central Valley’s missing fog.

Tule fog – a thick, white, low-to-the-ground veil of condensation that shrouds the valley on winter mornings – has been slowly vanishing over the past three decades. Foggy days steadily increased between 1930 and 1970, but have since declined.