In the Valley we live in a kind of bowl, surrounded on all sides by mountains that hold in the general haze all year. During winter there is morning fog that lingers. When it lifts, it reveals a solid-gray low cloud cover that last to about March or April, when we have 3 or 4 good days- followed by a blistering summer.
We visited the LA area for thanksgiving- clear-blue skys all day. As we drove back into the Valley it reminded me of Humphry Bogart in "The African Queen"-- going back into the the leech-filled river to pull his boat.