Avalanche Forecast
Issued: Dec 29th, 2019 3:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
cgarritty,
Avalanche Canada
Our persistent slab problem has evolved into a low probability/high consequence scenario. Maintain diligent group management and keep avoiding classic weak points like shallow rocky start zones and steep convexities if you're venturing into bigger terrain.
Summary
Confidence
Weather Forecast
Sunday night: Clear periods. Light southwest winds.
Monday: Increasingly cloudy with flurries starting in the evening and 10-15 cm accumulating overnight. Strong southwest winds. Alpine high temperatures around -5.
Tuesday: Cloudy with flurries bringing approximately 5 cm of new snow, continuing overnight. Moderate south winds easing over the day. Alpine high temperatures around -6.
Wednesday: Mainly cloudy with continuing flurries bringing 5-10 cm of new snow and 2 day snow totals to 25-35 cm. Moderate southwest winds. Alpine high temperatures around -5.
Avalanche Summary
Reports from Saturday included observations of several recent small (size 1.5) natural wind slab releases. These occurred between 1800-2300 metres on steeper northeast aspects and featured crown depths of up to 40 cm.
Small loose dry avalanches were observed out of extreme terrain over the weekend.
Last weekend there were reports of numerous natural and explosive triggered avalanches up to size 2.5
Snowpack Summary
Recent moderate westerly winds are likely to have blown around 15-30 cm of recent low density snow into soft wind slabs in alpine lees.
Below the recent snow, 60 to 120 cm of older storm snow is resting on a widespread layer of large, feathery, surface hoar which we're calling the "December 12th Surface Hoar." This layer was the primary failure plane in the large natural avalanche cycle observed last week. Activity on this interface has tapered off, but there remains some uncertainty as to how quickly the snowpack is gaining strength.
A weak layer formed in late November is now buried around 1 m or more below the surface. This interface may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect.
Terrain and Travel
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Caution around convexities or sharp changes in terrain.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
Problems
Persistent Slabs
A weak layer of surface hoar exists 60 to 120 cm below the surface. Natural activity on this layer is no longer expected, but human triggering may still be possible in suspect areas like shallow, rocky start zones or steep convexities.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
15-30 cm of new snow coupled with moderate southwest wind is likely to form fresh wind slabs in exposed alpine terrain features.
Aspects: North, North East, East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Dec 30th, 2019 5:00PM
