From GU Energy, the science behind staying hydrated while being active outside during the winter months:
Other than dressing properly to not over- or under-heat, athletes need to be aware they will have increased water loss and decreased thirst while exercising in the cold. All the same principles for maximal exercise performance exist in both cold and warm environments. These principles include making sure to start exercise in a hydrated state, and consuming enough fluids during exercise to prevent dehydration and the decrease in performance it brings.
It’s chilly, but get out and enjoy the sunshine!
Link to Dehydration and Thermal Stress in Winter Sports at GU Energy.