I've saved the best suggestion for last. Here are some of the features you want in a winter coat:
1. Make sure it features down insulation. In spite of commercial advertising to the contrary, there is nothing warmer than down -- in my opinion.
2. Make sure it is rated. My coat is from L.L. Beans. It is rated to 20 degrees below zero (fahrenheit). It is quite warm. You can do even better than this at a mountaineering store if you need to.
Note that the ratings on coats are generally geared towards moderate activity. If you are planning on standing around gazing at the stars through your telescope, you may need to buy something that is even warmer.
3. Make sure it has a hood. This is important because it represents yet another layer. You should wear both a hat and a hood if it is very cold.
Ideally the hood will stick out in front of your face just like the hoods of Antarctic explorers you see in National Geographic. This traps air near your face. The fur lining that lines the hood is a further air trap. A natural fur can provide a further benefit; it reflects heat back to your face.
Unfortunately for warmth, the fur on my hood is cotton and acrylic.
4. Make sure that all openings on the jacket seal. This includes the top of the jacket and the sleeves. There should be a pull string that lets you adjust the waist so that you don't lose air out of the bottom.
5. Buy Women's Coats and Jackets that is long enough. I special ordered mine in a long size. The racks in the store did not carry one that was long enough to suit me.
Ideally, I want a winter coat to extend far down on my thighs and the sleeves to reach down to my hands. For more info about Coats and Jackets, Fleece Jackets, please visit www.coatsjacketswear.com.