When you meet someone newly relocated to the central valley of California the topic of weather will quickly be broached:
“Hot enough for you? Well lucky for us it’s a dry heat.”
“Winter’s pretty mild around here ‘cept…for the fog.”
At which point the newly arrived will probably answer, “Oh fog, no I’m used to fog, I grew up in [fill in the blank with the name of somewhere with anemic coastal style fog.]” Or better yet, they will tell you they grew up in the Midwest with snow blizzards. If you have good home training you’ll politely smile and welcome them to the area. If you’re not so well-mannered you’ll guffaw and tell them they have no idea what they’re in for. Either way, if you happen to meet up with these folks again a few months into “fog season” you’ll see their self-assurance has eroded and their eyes are bugged out and glassy. “This is way worse than any fog/snow I’ve ever seen. It’s soooooo thick!” Told ya (or wanted to tell ya) so!
Tule (too-lee) fog is a weather phenomenon unique to the central valley of California. Named after the Tule River, the fog is produced when moist air fills the valley bed and is trapped against the cold damp ground by an inversion layer of warmer air above. Essentially the vapor droplets in the fog freeze forming an impenetrable cloud on the ground.
Until I read Cai’s description of Tule Fog I thought it was everywhere. I had no idea that it was unique to California. I remember many times driving in fog so thick that it was impossible to see anything and being afraid to pull to the side of the road for fear of being rear ended. As a side note, it does not help to roll your window down and stick your head out–visibility does not improve. I looked at Cai’s Tule Fog postcard many times and thought I saw headlights in the fog. What I didn’t see (until the rug show at Friends-By-the-Sea where it was pointed out to me) was Tule Fog written as plain as day.