Weather variables, especially snowfall, affect the timing and duration of hazardous snow avalanche conditions. Snowfall amount, rate of accumulation, moisture content, and snow crystal types all contribute to the magnitude of unstable conditions. Wind is another critical weather variable capable of depositing large amount of dense snow into starting zones. Strong winds are capable of creating an unstable load rapidly even when little or no new snow has fallen. Because the prevailing storm track in Montana is west to east, east facing leeward slopes often receive the most snow from wind loading.
Temperature is a weather factor that affects the physical nature of the snowpack.
Low air temperatures over a thin, permeable snowpack cause a temperature gradient change weakening the snowpack and leading to an ongoing avalanche hazard as subsequent storms add to the snow load above this weak layer. This condition is most prevalent on north-facing slopes during winters with sever or prolonged low temperature events. High temperatures can also contribute to avalanche hazards by melting snow and reducing friction by increasing pore pressure in the snowpack. This condition develops best on slopes with southern exposure and the hazard is highest during the warmest part of the day. The complex interaction of all these weather and terrain factors contributes to the location, size and timing of avalanches.