Avalanche Forecast
Issued: Dec 13th, 2019 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
20-30 cm of new snow rests on a layer of surface hoar. Expect it to become touchy as it settles into a storm slab in the mild temperatures. Watch for shooting cracks and electric propagation, especially near openings in the trees.
Summary
Confidence
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
Friday Night: Mainly cloudy, isolated flurries with trace accumulation, alpine low -6, light northwest wind.
Saturday: Mainly cloudy, isolated flurries with trace accumulation, alpine high -6, light northwest wind.
Sunday: Mix of sun and cloud, isolated flurries with trace accumulation, alpine high -10, moderate northwest wind.
Monday: Mix of sun and cloud, isolated flurries with trace accumulation, alpine high -10, moderate northwest wind.
Avalanche Summary
Reports from Thursday and Friday mostly describe sloughing and small loose dry avalanches up to size 1. Soft storm slabs propagating at ridgetops but breaking up quickly as they ran, were also limited to size 1.
Prior to the new snow, numerous natural, explosive and skier triggered avalanches size 2-2.5 on a variety of aspects have been reported recently throughout the region and in neighboring Glacier National Park. Some of these avalanches were triggered in areas of shallow snowcover or wind slab and stepped down to the persistent November layer resulting in avalanches large enough to injure or bury a person.
Snowpack Summary
20-30 cm of new snow has covered a widespread layer of large, feathery surface hoar crystals. The new snow can be expected to gain cohesion and settle into a slab in the mild temperatures, especially at treeline and below.
The new snow also buried soft wind slab found in the lee of features such as ridge tops, ribs and gulleys.
A weak layer formed in late November is now buried around 1 m below the surface. This is the layer of concern relating to the persistent slab avalanche problem. The weak layer may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. It can most likely be found in areas sheltered from the wind, but open to a view of the sky, such as near treeline. Below this, variety of crusts from late October are buried deeper in the snowpack.
Problems
Storm Slabs
20-30 cm of new snow is expected to gain cohesion and settle into a slab in the mild temperatures, especially at treeline and below. It sits over a widespread weak layer of large, feathery surface hoar crystals. This can be a recipe for touchy storm slab avalanches, sometimes involving remote triggers and wide propagation.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
This weak layer formed in late November may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. It is buried around 1 m below the surface and can most likely be found on steep south-facing slopes or in areas sheltered from the wind, but open to a view of the sky.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 14th, 2019 5:00PM
