Avalanche Forecast
Issued: Mar 16th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
kklassen,
Avalanche Canada
Watch for lingering wind slabs in the alpine. New soft slabs formed below treeline on the weekend and overlie a persistent weak layer of surface hoar--this creates the unusual situation where low elevation danger remains a concern while upper elevations gradually improve.
Summary
Confidence
Weather Forecast
Monday Night: Flurries possible but no significant accumulation. Moderate to strong winds changing from westerly to northerly at ridgetop. Light and variable winds below treeline. Temperature falling to -10 or so. Mostly cloudy.
Tuesday: No significant precipitation. Light to moderate wind from the northeast at ridgetop. Light northeast winds below treeline.Temperatures -5 to -15. A few clouds.
Wednesday: No significant precipitation. Light winds from the north and northwest at ridgetop. Calm to light and variable winds below treeline.Temperatures -5 to -10. A few clouds.
Thursday: No significant precipitation. Light and variable winds. Temperatures -5 to -15. A few clouds.
Avalanche Summary
A wind slab avalanche cycle up to size 2.5 was observed on Saturday. One size 3 was reported on a south aspect as well. No avalanches were reported at lower elevations where surface hoar is known to exist but observations are scarce.
Natural avalanches are unlikely in the next few days as a cooling trend occurs. However, human triggering of isolated lingering wind slabs at upper elevations remains a possibility, especially on steep southerly slopes if the sun is strong. At lower elevations, human triggering of avalanches is also possible where slabs, even very soft ones, may now exist over persistent weak surface hoar layers, again perhaps somewhat more likely on sunny slopes.
Snowpack Summary
Temperatures had less of an effect over the weekend than expected but the sun was strong enough to create a new surface crust on steep southerly terrain, probably more so at lower elevations. Winds have continued to transport snow at upper elevations creating new wind slabs in some areas that were unstable on Saturday. At lower elevations, winds have created soft slabs in open areas below treeline. Two surface hoar layers 50-60cm and 75-90cm below the surface remain a concern especially if there's a slab on the surface from warming and/or winds over the weekend.
A cooling trend will likely tighten the bonds in the snowpack for the next few days. In the alpine, where windslabs are the main issue, this will probably improve some of the instabilities that came up over the weekend. However, at lower elevations more cohesion in the upper snowpack could actually increase the sensitivity of the persistent weak layers of surface hoar.
Terrain and Travel
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Approach lee and cross-loaded slopes with caution.
- Be very cautious in open terrain features, such as cutblocks, gullies, and cutbanks.
Problems
Wind Slabs
Winds on the weekend created new wind slabs on south, southwest, and west aspects--these are the primary concern. However, older wind slabs on most aspects from highly variable winds last week are still lingering so expect a mixed bag on all aspects in exposed terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Watch for places where weekend winds or warming and then cooling have created slabs in open areas. These slabs will probably be soft and might be quite subtle. While size is not expected to be large, be wary of terrain traps like treewells or creeks and ravines where debris piles up deeply even from small slides.
Aspects: All aspects.
Elevations: Below Treeline.
Likelihood
Expected Size
Valid until: Mar 18th, 2020 5:00PM
