Temperature can be a difficult forecast in winter. Once the ground is snow-covered, a layer of cold air tends to form over the snow at night and then persist throughout the day. This cold layer is often several hundred feet deep. Because cold air is denser than warm air, any incoming warm air tends to blow over the top of the cold air, creating a temperature inversion. The degree to which this warm air above can be mixed down to the ground (where we can experience it) varies greatly based on other weather conditions. Sometimes, a windy day will mix the air and bring warmer air to the surface, but forecasting this is tricky. When the ground has no snow cover, this boundary layer is easier to break because of daily rising thermal currents coming off the sun-heated ground. When the ground is snow-covered in winter, however, temperature forecasting can be a bit of a guessing game.
