Avalanche Forecast
Issued: Dec 28th, 2019 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
ahanna,
Avalanche Canada
The persistent slab problem is evolving into a low probability/high consequence scenario where you may not observe any indication of instability before making a dangerous decision. The formation of new wind slabs up high will add a layer of complexity to terrain selection.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Saturday night: Mostly cloudy, isolated flurries with trace accumulation, alpine low -9 C, alpine wind moderate from the southwest.
Sunday: Scattered cloud, alpine high -7 C, alpine wind light southwest.
Monday: Scattered cloud, flurries starting in the pm accumulating 5-10 cm overnight. Alpine high -7 C, alpine wind building through the day to strong west overnight.
Tuesday: Mostly cloudy, flurries accumulating up to 5 cm, alpine high -5 C, alpine wind tapering to light west by evening.
Avalanche Summary
Small loose dry avalanches were observed out of extreme terrain over the weekend. No new slab avalanche activity has been reported since Monday.
Last weekend there were reports of numerous natural and explosive triggered avalanches up to size 2.5
Snowpack Summary
Moderate westerly winds are likely to have blown around 15-30 cm of new snow, forming soft windslab in alpine lees. Anywhere from 60 to 120 cm of 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 culprit for the large natural avalanche cycle last week. Activity on this interface has likely 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
The old storm snow is slowly settling into a slab which rests on weak surface hoar 60 to 120 cm below the surface. Natural activity on this layer may have cycled out, but human triggering may still be possible, especially in more challenging/complex terrain.
Aspects: All aspects.
Elevations: All elevations.
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 29th, 2019 5:00PM
