Forecast of the Day • A National Weather Forecasting Contest

OK, here's one final day with a forecast at the edge of a cold air mass. Models show the next big push of cold air arriving in Glasgow, in northeastern Montana, late Friday. The minimum temperature forecast will depend on whether the temperatures start dropping rapidly before or after the end of the day (11 pm MST). So let's forecast Friday's Tmin and see when the cold air arrives.

And here is the NWS discussion talking about how this February has been: "Update on records at the NWS Glasgow office: Feb 2019: 2nd coldest Feb on record through midnight. The average temp is -3.9F or 22.8 degrees below normal. 2018 was the 6th coldest on record. 1936 is the coldest on record at -15.8 for the average temperature for the month!" And also this: "Feb 2019 is the snowiest February on record with 28.2" of snow."

Question: The NWS discussion also says that they are lowering forecasts because of the extensive snow cover they currently have. Why does snow cover lower the expected temperatures?