Of course they are not really a boundary for upper air, like the fire smoke that blows out to sea on satellite photos, but on the ground, where people experience the weather.
Whenever I anticipate hiking or leading field trips at Malibu Creek, Red Rock or Solstice Canyon, I check not only Malibu’s predicted weather, but Calabasas or even Agoura, because the North side can be considerably hotter. The ocean water has a ‘higher heat capacity,’ meaning it acts as a reservoir of temperature and does not heat up or cool off as quickly as the air over land, or the ground itself. Malibu can regularly be in the 60’s and 70’s, while the North side can be 80’s and 90’s on sunny afternoons, not pleasant for hiking.
Strong winds are always steered through (and sometimes compressed in) canyon passes, so make gusts the way freeway corridor walls and large trucks do. Air flows as a fluid, from high to low density, downward by gravity or upward with lightness and heat (convection). When a truck blasts by on a freeway, air rushes in behind it, so bursts push lightweight cars around in the lane, the way desert and ocean winds do when they meet on L.A.’s coastal plain. If you watch regular patterns and then use your imagination to picture the invisible air molecules, it’s easy to understand.
One time on a January morning, I was leading a NPS ranger training workshop at Satwiwa near Newbury Park (Rancho Sierra Vista, where they have a cool waterfall on the back side of Boney Mountain, on a non-drought year). Malibu Canyon was 62 degrees on the (south) coastal side, and on the north Calabasas side, 39 degrees! One ranger said they call them “sinks” on the North side.