Your explanation is very good. Here is my modification 시원하다 used in the summer, when you feel refreshed with cool breeze. 선선하다 used in the early fall, when feel refreshed with a little low temperature(you get a little goose bumps after long exposure.) 서늘하다 used in the mid fall, when you feel a little chilly(you will get goose bumps at once). 쌀쌀하다 used in the late fall, early winter, when you feel chilly. Here are some words of such categories 사느랗다, 사느랗다, 사늘하다, 살랑하다, 서느렇다, 설렁하다, 싱겅싱겅하다, 싸느랗다, 싸늘하다, 쌀랑하다, 써느렇다, 써늘하다, 썰렁하다