First know the weather and how to take care of yourself when you are working in the cold.
Cold Related Illness and Emergencies
Then how to dress: When working in cold weather, you need to dress in layers that will wick away moisture, insulate from the cold, and keep out the wind and rain. From head to toe and inside to outside, here is what to wear.
Use the Layering Principle
Base Layer: Wicking fabric to keep your skin dry and prevent that clammy feeling.
Insulating Layer: Fleece or wool, vest or shirt that can be added or removed depending on how cold you feel.
Windproof and Water-Resistant Outer Layer: A jacket, preferably with a hood, to keep out the elements.
The following are some websites about the cold and being in it.
The Ironman's Tips for Staying Comfortable While Observing in Cold Weather CDC Winter Weather | A Prevention Guide to Promote Your Personal Health and Safety