Earlier in the episode it is mentioned that the temperature was -10 °F, at the end of the episode Abby states that it must be getting warmer because it started snowing. It is actually a common myth that it cannot snow below certain temperatures, while it is true snow is a lot less common when the temperature is below 0 °F it can still snow at any temperature. The only temperature where it would be impossible for snow to form would be absolute zero, as it is impossible for matter to exist at that temperature, or lack of temperature to be accurate.