LAST EDITED ON Sep-09-08 AT 10:13AM (MST)[p]It only seems light and thin because us hunters are so used to bulky and thick jackets made by most hunting clothes manufacturers. Sitka is different, it's based on mountaineering designs. Have you ever seen a high quality soft shell jacket from a company like North Face, Mtn Hardware, Arcteryx, etc? They are very similar to the Sitka jackets. Rather than big bulky insulation they instead use higly efficient insulation and a layering principle. Sitka uses body mapping to determine where your body loses heat and really needs insulation and where it does not. It is elimated in places where we don't need insulation and that reduces bulk. It also uses Polartec fleece which is very efficient and retains much more heat with less fabric than other types of insulation. It feels thin and fits trim because it is supposed to be. That way you can move about and it moves with you. You can draw your bow or shoot your rifle without interference. You will be able to hike easier and will have more range of motion. The 4 way stretch fabric is awesome. You won't feel like the Michellin Man like you do with some bulky hunting jackets.
To answer your question, yes I think it will be warm enough. Partner the Celcius jacket with a good base layer, the Celcius vest, Traverse Shirt, or a good sweater, and you will be plenty warm enough.
You will want at least the 90% pants for what you are describing. The Celcius bibs would be an even better choice for real cold. The Traverse pants are good for early season, they are not designed to be warm. The 90% pant is the next step up in warmth and the Celcius bib is the ultimate.