Avalanche Forecast
Issued: Feb 27th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
shorton,
Avalanche Canada
Warm temperatures and sunny breaks could weaken the upper snowpack. Really watch your exposure to overhead hazard, it would be easy to be surprised by weird avalanches on Friday.
Summary
Confidence
Low - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.
Weather Forecast
THURSDAY NIGHT: Cloudy, moderate southwest wind, freezing level drops to 1000 m overnight with alpine temperatures around -4 C.
FRIDAY: Mix of sun and cloud, freezing level climbing to 2000 m in the afternoon, moderate wind with strong gusts from the southwest. Increasing cloud and light snow starting in the evening.
SATURDAY: Cloudy with 3-8 cm of new snow, moderate to strong wind from the southwest, freezing level drops from to 2000 to 1400 m.
SUNDAY: Mix of sun and cloud, light wind from the west, freezing level reaches 1500 m in the afternoon.
Avalanche Summary
On Thursday a few small cornice falls were observed near Elkford, one of which triggered a size 2 slab on the slope below. A few small (size 1-1.5) slab avalanches were triggered by skiers on Tuesday and Wednesday, including a small storm slab that may have failed on surface hoar.Â
The most recent deep persistent slab activity we know about is described in this MIN report from February 11 and this MIN report on February 9. This layer may become reactive again with warming temperatures and the appearance of the strong late winter sun.
Snowpack Summary
The 10 to 35 cm of snow from Sunday/Monday has been absolutely hammered by wind Wednesday as evidenced in this MIN submission. Wind was strong enough to get into below treeline features even. Wind stiffened slabs now rest on a variety of old surfaces including a firm crust on solar aspects, soft faceted snow, possibly surface hoar in sheltered areas, and old wind slabs near ridge crest.Â
A thick rain crust sits 30-60 cm below the surface and can be found up to 2100 m. Avalanche activity was last observed at the faceting interface between this crust and overlying snow on February 17.Â
The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.
Terrain and Travel
- Avalanche hazard is expected to to increase througout the day, think carefully about your egress.
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
Problems
Wind Slabs
10 to 35 cm of storm snow was heavily affected by shifting wind Wednesday that even got into tree'd terrain. As temperatures warm and the sun comes out over the next few days human or potentially even natural avalanches become more likely.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Weak snow at the bottom of the snowpack hasn't gone away unfortunately. As temperatures warm and the strong sun comes out over the next few days we need to be thinking about the potential for large destructive avalanches. Cornice failures become more likely during these kinds of conditions and a failing cornice could be the perfect trigger for the deep persistent slab. Human triggering would be most likley around steep rocky terrain features, or anywhere the snowpack is thin and weak.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 28th, 2020 4:00PM
