If you're in the Tule fog, your humidity and dewpoints are going to be at saturation, so why would you irrigate? Virtually all of your plants (including palms) are likely to have fully open stomata in these conditions and are surely gorging themselves on the atmospheric moisture in addition to what they can harvest from your soil moisture. And of course your soil-structure/composition is all important in figuring this out in your situation once your humidity and dewpoints decrease. I'm sure your Rhopies would be just fine with irrigation since it's plenty chilly and wet where they come from, but IMHO it would just be a waste of your $$$ to do it, particularly if they're established.
I agree with what Tom Blank says above, and will add anecdotally that I lived on Big Pine Key in the hot, hot Florida Keys with very little rainfall for months at a time and brutal tropical sun bearing down, particularly in springtime with few clouds and near-zero rain. On a limestone rock, basically. And very different from Miami and much of mainland Florida, where there is land and convection to make rainfall, the Keys have nothing really to generate any rain on their own. And yet they are covered in vegetation. The Lower Keys have a freshwater lens that plants can tap into (it was about 3' deep at our house) if their roots can reach, but I had many plants--containerized, planted or native--that just survived almost entirely on the perpetually high humidity and the occasional bit of rainfall for all that time. And in the upper Keys (e.g., Islamorada and Key Largo) there isn't any groundwater, and yet plants survive there as well during the dry season. Many parts of the world have similar situations where there isn't much regular rainfall, and yet plants can do just fine using whatever atmospheric or soil-based resources are at hand, through drought and deluge.
I now find myself in the Palm Springs area, where it is much, much drier in winter than either Florida or the Central Valley of California where you are, and palms here are generally still growing albeit at a very slow pace, I reduce irrigation markedly for the cool season, but don't turn it off completely. I factor in, additional to simple observation and past experience, the individual needs/metabolism and stress-tolerances of the plant; soil composition/structure (our porous sand and DG/granitic alluvium); sun/shade exposure and positioning; our low atmospheric humidity, in which water transpires out so very quickly; and the level of establishment of the plants (in my garden usually about three years for most plants to establish a far-ranging root-system). I change cool-season distribution of irrigation to one-minute spurts late morning and very early afternoon where solar warmth is still incoming (and always water containerized plants about 10-11am for that reason)...I avoid any late-day irrigation, which will likely deliver quite an unhealthy, wet chill to the roots of any tropical lowland plants.
You'll of course have a very different situation where you are in Fresno, but this just to illustrate that I think all of the above factors have to be considered by anyone in delivering the right amount of irrigation, always keeping in mind the often very diverse native climes from which our garden plants originate.