California has always had periodic cold-waves with terrible freezes...1913, 1925, 1937, 1949, 1990 and 2007 being amongst the most (in)famous. But in general the immense barrier of the Rockies and the various other mountain ranges of the Western USA keep the cold flowing east. And the mighty Pacific generally acts as a tremendous moderator. But it does happen. But nowadays it's more of an agricultural issue than it is one for tropical ornamental horticulture, since the latter generally exists in developed suburban, semi-urban or urban landscapes with their broad UHIs, as noted by Nathan above; and agriculture has been chased out to less hospitable areas by the power of the developer and the mighty dollar.
But as in most places, many plants will be damaged but recover, others will die, and provide gardeners and landscapers with open spaces for something new. Not always a bad situation, in fact an assist to overplanters or those who purposely utilize marginally hardy fillers to round out a young landscape. And there are areas that get scorched by cold most years, even right next to the coast, this due to the particularly varied geography and topography in the west. The nursery industry is no stranger to it, and replacement plants are a healthy part of the plant industry. Also one must keep in mind that, not only are the most severe events east of the Divide more spectacularly cold than in the west, but also the very tender landscaping materials used in Central and Southern Florida are far more pervasive there as compared to the generally more conservative landscapes encountered in most of California, and I believe also in Southern Arizona and Southern Nevada...so the effects are usually much less noticeable in the southwest. But yes, it can fill those of us with large collections of tender materials with a similar angst, to be sure. But at the end of the day you have to readjust, learn, and move on within your level of comfort.
Also, I notice that you posted a wind-chill temperature map, rather than the 2m temperature map. Remember that wind-chill is irrelevant to plants, as it only affects animals. Plants can be dried out by the intense, dessicating winds that often accompany extreme cold events, but it's not "wind chill" as is usually equated with the effect of a lower temperature.