Career mode is using live weather (within the last 24h, see below), but apparently there are ways to turn it off in the latest updates. I haven’t tried them, so someone else could probably answer that better.
Anyway, I have a whole long thread explaining how the weather system appears to be intended to be used in career mode.
It can be localized with mountains, absolutely, but there are a lot of other indications and forecast tools that can give you an idea of the general conditions and probabilities of adverse weather. The deal is you’re diving into stuff that’s pretty deep into the syllabus of a real-world pilot, so it isn’t always easy to pick up in a short conversation. Bottom line, if it’s the warm season, it’s generally best to fly in the mountains before 10AM, haha.
Eh, the SF50 isn’t that fast. 
Doing an overhead or even a low pass along the runway isn’t unheard of at less-improved fields. It’s certainly not preferable to not do a straight-in or a normal pattern in a light jet, but again, there are prudent, real-world techniques you can use when you’re flying into fields like that.