Can I wear this jacket by itself in the winter and be warm enough?
No not for cold winters. This jacket is more suitable for 30 degree F or greater temp. It does not have much insulation so a few minutes out in the real cold and you will start to feel it.
I always wear this by itself with just Tees or Polo Shirt and it still keeps me warm.
I live in Toronto, ON, Canada and this is at best a late Fall, early winter jacket. This jacket has a windproof shell but has no insulation like a down jacket. I would say it is good for above freezing temperature at best.
Depends on where you live. It's a good jacket for temps around 35-45 degrees for short periods but you also can't wear a lot under the jacket as it is fitted.
Most people would not consider this jacket warm enough for extended periods of time outdoors in the winter. It is quite thin. Blocks the wind well but lacks proper insulation.
Depends on where you live. It's a softshell with a light fleece texture inside. Great windstopper, but not insulated. With a down vest or sweater inside, pretty warm. I use it for spring skiing in New England.Not for midwinter conditions.