I’ve been continuing to think about my mental map of the seasons.
Wet Fall — usually starts at the beginning of November, but can start as early as mid-October or as late as mid-November. Lasts definitely through November and well into December. Daytime temps start in the mid50s and gradually decline to the mid40s. Rain. And if not rain, then overcast. These are the days for which the region is famous. Occasional overnight freezing, but for the most part the temperature is remarkably constant, drops less than 10 degrees overnight. Most likely dramatic weather is the Pineapple Express — warmer wet weather that comes from the tropics, often with wind, usually with flooding.
Icy Winter — usually starts mid-December; if there’s a “real” snow in December, that’s the start. Otherwise, right around the solstice. Lasts through January, occasionally into early February. Daytime temps range from mid30s to low40s, with most overnights right around freezing, but can be quite a bit colder. A stretch of overnights in the low 20s and daytimes right around freezing isn’t uncommon. If we get any noticeable snow, it’s during this season. Can have stretches of very bright clear days, which are almost always also very cold. This weather often comes with freezing fog.
Wet Winter — usually starts after the last chance of “real” snow at the beginning of February, and lasts through the last stretch of really cold weather in mid-March. This looks a lot like Wet Fall, but less dark only because the days are longer. Gradually warms up out of the 30s and up into the low 50s. Almost always includes a “fake out” day that feels like spring, usually in mid-February. There WILL be a frost after that date.
This is mostly based on my personal experience, so it’s really only good for Olympia and Tacoma. YMMV in other parts of the Pacific NW.