Ever since my first experience of "unprepared for terrible weather", I always check the weather forecast diligently, and I always make sure I bring one extra jacket, just in case the weather forecast is not accurate.
Even though I prefer cool weather over hot weather, still, I learn all the tips of keeping warm, and I equipped myself well. Last year, I got myself an Ultra Light Down jackets from Uniqlo, which is so light and compact that I can squeeze it into one of the lens compartment in my camera backpack. That is my "to bring" item whenever I travel in spring, autumn and winter :)
For our upcoming family trip, the weather forecast looks great! "Abundant of sunshine" makes me happy and "Brilliant sunshine and warm" sounds awesome!