WeatherTalk: The woods are lovely, dark, and deep ... and also cold
Trees are a drag force on the wind, which helps cold air collect and sink to the ground.
FARGO — On cold nights, it is often noticeable that the coldest low temperatures occur in wooded areas of northern Minnesota rather than out on the flat plains of the Dakotas. Flat terrain encourages more wind and lower wind chill values because the flat terrain offers much less roughness to slow down the wind.
When there is very little wind, colder pockets of air will sink down to the ground and then drain into low spots of ground simply because cold air is denser and heavier than warmer air. Even a very light wind will help keep the air mixed up and keep these cold pockets of air from collecting near the ground where the air temperature is measured. In the North Woods, the trees act as a drag force on the wind and are more likely to generate the perfectly calm air that favors the sinking and collecting of very cold near the ground.