Avalanche Forecast

Fair - Intensity of incoming weather systems is uncertain

Thursday: A storm is expected to bring 10-15 cm new snow with freezing levels around 900 m and ridgetop winds around 60 km/h from the southwest. Friday: The storm is expected to intensify, with a further 20-30 cm new snow for higher snowfall areas. Freezing level is expected to rise to around 1300 m late in the day. Strong ridgetop winds are expected to shift from southwest to northwest. Saturday: Dry. Freezing level around 500 m. Winds light or moderate.

In recent days, a widespread natural avalanche cycle took place to size 3.5 in response to loading from heavy precipitation, wind and warm temperatures. Many avalanches failed within the recent storm snow, although numerous avalanches also failed on persistent and deep persistent layers. Most of the avalanche activity had subsided by Tuesday 27th, although human triggered avalanches were reported to size 2 and explosive controlled avalanches were reported to size 2.5. With forecast snow and wind, I expect ongoing storm slab activity, and the potential for deep destructive persistent slab avalanches remains.

Moderate to heavy snowfall (with rain at lower elevations) and strong southwest winds have built deep and dense storm slabs. These storm slabs are expected to be most reactive in wind-exposed, upper elevation terrain. A rain crust and/or surface hoar layer buried mid-January can be found about 100cm below the surface, the depth varying greatly depending on whether the slope is wind-loaded or wind-scoured. This persistent weakness was very reactive during the last storm loading, and was responsible for much of the recent large avalanche activity. The structure of this layer has been reported to have been changing rapidly, and this is consistent with a warm, rapid loading event such as the one last weekend. Still, I would recommend giving this layer a little more time to bond before discounting it from the avalanche equation.The November crust near the bottom of the snowpack was thought to be well bonded. However, this deep and destructive layer "woke-up" in response to heavy snowfall, wind and warming over the last few days producing very large avalanches in isolated terrain.