Every ski resort publishes a "conditions" report or a "ski report".  Usually it's done daily and gives you a summary of the temperatures, trails open, lifts running, weather conditions, and more.

Here's some tips to keep in mind for different temperatures:


40° AND ABOVE
  Torso:  Turtleneck or shirt or T-shirt, plus wind shirt or light jacket.
  Legs:  Pants only.
  Head/Face:  Light hat or none.  Goggles to cover eyes.
  Hands:  Light gloves or liners.
  Feet:  Light socks.
Put lift ticket on a garment that will not be removed.

28° TO 40°
  Torso:  Turtleneck or shirt plus medium parka or jacket.
  Legs:  Long johns and pants; or pants and warm-ups; or bib ski pants.
  Head/Face:  Light or medium hat.  Goggles to cover eyes.
  Hands:  Medium gloves or wool mittens.
  Feet:  Light socks.

15° TO 28°
  Torso:  Turtleneck, light sweater, and medium to heavy parka or jacket.
  Legs:  Thermal long johns and heavy pants; or medium pants and warm-ups; or long johns and bib ski pants.
  Head/Face:  Medium to heavy hat.  Goggles to cover eyes.
  Hands:  Heavy gloves or wool mittens with liners.
  Feet:  Medium socks.

5° TO 15°
  Torso:  Turtleneck, shirt, medium sweater or vest, plus heavy parka or jacket.
  Legs:  Thermal long johns, pants and warm-ups; or thermal long johns and bib ski pants.
  Head/Face:  Heavy tight-knit hat that covers ears and forehead.  Goggles to cover eyes.
  Hands:  Heavy gloves or heavy wool mittens with liners.
  Feet:  Wool socks.

5° AND BELOW
  Torso:  Thermal undershirt, turtleneck, shirt, heavy sweater or vest, plus heavy parka or jacket.
  Legs:  Heavy thermal long johns, heavy pants and warm-ups; or heavy thermal long johns and bib ski pants.
  Head/Face:  Salve on face.  Face mask or scarf and neck gaitor over mouth and nose.  Goggles to cover eyes.  Heavy tight-knit hat that covers ears and forehead.
  Hands:  Heavy gloves with liners or heavy wool mittens with liners and windproof shell.
  Feet:  Wool socks. Keep boots loose to aid circulation.  If windy, add another layer to torso. No exposed flesh on head. Add hood to parka if available.