I'm from Ohio and in my area, thunderstorms are incredibly common. Like, most of the time it rains it's usually a thunderstorm. I'm writing a story that takes place near Sacramento, California and at one point in my story there is a thunderstorm. I never thought this would be a problem, because I always thought that thunderstorms were a common, ubiquitous, universal thing pretty much everywhere. But then today I find this map, which has me worried: ...and I look at the area between San Francisco and Sacramento, and I see absolutely no yellow at all! Now I'm confused, because it appears everything west of the Rockies is an entirely different planet with totally different weather! Is it really that far-fetched to have a thunderstorm in northern California? Do they really never happen, like at all? Are readers going to call BS when they see the word "thunderstorm"? Or might there be ways I can get out of it? To me, "thunderstorm" is synonymous with "rain" because like I said, when it rains in my area it's usually a thunderstorm. But I also know it rains incessantly in Seattle, and I see no yellow there either, so could I maybe make it a regular rain storm? Or do those not happen in the Sacramento area either? At this point I'm kinda questioning everything I know...
I'm from Sacramento. We do have thunderstorms here once in a great while, but not nearly as often as on the east coast (where I spent much of the first part of my life). Maybe once or twice a year. More often it's thunder and lightning, without the rain.
I live in a tourist town in Oregon that has thunderstorms. One summer evening I was eating at a restaurant that had a good view of the nearby hills, when a thunderstorm started in those hills. The Californian tourists temporarily abandoned their meals and went outside to watch the fascinating novelty. (Edited to note: Huh. The area that my town is in also shows as having no thunderstorms, on your map. But we have at least a few a year. Or maybe just a couple. More than none.) On the other hand, when I lived in the Bay Area, where I more than once said, "Yes, we have earthquakes, but at least we don't have tornadoes," a tornado took out a tree on my employer's campus. I think that you can have your thunderstorm, but it should be exciting and surprising.
If you google Sacramento Thunderstorm, you get hits. There's a YouTube clip at that sounds like a pretty typical storm where I'm from, but one of the comments says it's the best storm he's seen in 50 years in Sacramento. So, yes, sometimes storms, but not as often? (or - what @ChickenFreak said)