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Avalanche Forecast

Archived

Dec 15th, 2018–Dec 16th, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

Watch for unstable snow on steep and wind loaded terrain features.

Confidence

Low - Due to the number and quality of field observations

Weather Forecast

SATURDAY NIGHT: 10 cm of snow as a front passes overnight, strong wind from the southeast, alpine temperatures around -10 C.SUNDAY: Flurries easing throughout the day with 3-8 cm of snow, wind easing from strong to moderate throughout the day from the south, freezing level up to 700 m with alpine high temperatures around -3 C.MONDAY: Mainly cloudy with isolated flurries and localized accumulations of 5 cm, strong wind out of the south, alpine high temperatures around -3 C.TUESDAY: 5-10 cm of snow, strong wind out of the southwest, alpine high temperatures around -3 C.

Avalanche Summary

Several natural slab avalanches were reported during the stormy weather over the past few days. Two large (size 2) avalanches were observed on east-facing wind-loaded slopes near treeline (1700 m) and several smaller slabs have been reported in steep gullies at lower elevations. See this MIN report. These avalanches are likely running on the interface between the storm snow and old snow roughly 20-40 cm below the surface. This slab has produced notable cracking with skier traffic and could produce large human triggered avalanches on steeper slopes.

Snowpack Summary

20-40 cm of new snow has covered the region so far this week, the product of an ongoing series of storms. Areas like Howsons in the far southwest had storm totals closer to 50 cm. The combination of new snow and forecast strong south winds is likely forming thicker and more sensitive wind deposits at higher elevations. Even below the wind, the new snow will need a bit more time to form a good bond with the weak surface hoar and facets that were sitting on the surface prior to the storms. (See this MIN report).Deeper in the snowpack, there are reports of several crusts including an early season crust with facets near the bottom of the snowpack.The new snow has brought alpine snow depths up to 100-150 cm and started to cover the rocks, stumps, and open creeks at lower elevations.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.