@AmeliaNG In addition to @CGrant56's excellent tips, the method I normally use is I deactivate weather effects on sims. This can be done in the game save by going to 'Game Options' > 'Seasons' > and un-check the box that says "Enable Temperature Effects On Sims". Personally, I do this because of the issue you're complaining about... the sims do not always automatically change to the weather-appropriate clothes they need to keep themselves from 'overheating to death' or 'freezing to death' (life-threatening conditions). I see this as unfair and inappropriate to proper/logical gameplay, so until this (hopefully someday) is different, I uncheck this box & save settings.
There are some bug reports on freezing and weather effects on the sims at this link: https://answers.ea.com/t5/Bug-Reports/READ-FIRST-Compiled-list-of-reported-Issues/m-p/7962773#Weather14
