Weather Factors

Cold temperatures extend the time it takes for the snow to set and is generally associated with instability and poor binding in the snowpack. Slow warming during the day and cold nights is favorable for the bonding between layers in the snowpack. In general, the snow is most stable when it is hard. Intense warming during the day or heavy rainfall can create instabilities and trigger weak layers deep in the snowpack. Keep in mind: The snow conditions and their associated avalanche danger will change dependent on the time of the day.

Strong winds will transport snow, where it settles in gullies, bowls and troughs on the lee side of the mountain. Wind transported snow can quickly form cohesive slabs on top older snow layers - which can be triggered as slab avalanches. After periods of high wind, riders should be extra careful in the transitions between hard and soft snow. If in avalanche terrain, the weight of the rider can propagate weak layers below this new wind slab, causing the softer wind slab to slide on top of the hard windblown surface.

In general, there is not a direct correlation between high amounts of new snow and high avalanche danger. This is due to the interation between snowfall, temperature, and wind. As a rule of thumb, you should be careful if more than 30 cm (12 in) of new snow has fallen in a 24 hr. period. But in cases where temperatures are closer to freezing, and wind transportation is low, the critical amount of snow can increase to 60cm. On the contrary, if temperatures are very cold, and there has been a high amount of wind transportation, then as little as 10 cm (4 in) can lead to dangerous avalanche conditions. Critical amount in favorable conditions: 30-60 cm during the last 1-3 days. Critical amount in unfavorable conditions: 10-20 cm during the last 1-3 days.