Be aware that temperature decreases with height, though the magnitude of the decrease is difficult to determine with accuracy due to the large number of contributing factors: shade, sun, nearby buildings (or lack of them) and inversions (colder air sinking into valleys because it’s heaver than warm air) among them.
Atmospheric pressure is simply the weight of the air pushing down on you from above. As you increase in elevation, there is less air above you thus the pressure decreases. As the pressure decreases, air molecules spread out further (ie air expands) and the temperature decreases. If the humidity is at 100 percent (because it’s snowing), the temperature decreases more slowly with height.