Avalanche Forecast
Regions: Northwest Inland.
Stick to sheltered terrain to avoid the intense wind transport and dangerous avalanche conditions on Tuesday.
Confidence
Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the complexity of the snowpack’s structure.
Weather Forecast
A windy storm will continue until Wednesday afternoon.
MONDAY NIGHT: Isolated flurries with up to 5 cm of snow, strong southwest wind, temperatures around -8 C
TUESDAY: Scattered flurries with 5-15 cm of snow throughout the day, strong to extreme south wind, temperatures around -4 C.
WEDNESDAY: Flurries continue with another 5-10 cm of snow by the morning then clearing in the afternoon, moderate south wind, temperatures around -6 C.
THURSDAY: Partly cloudy, moderate south wind, temperatures around -8 C.
Avalanche Summary
Over the weekend there were several reports of natural size 1-2 slab avalanches on northeast alpine slopes (see some photos here and here). Most of the activity was on wind loaded slopes. There was also a size 1.5 skier controlled storm slab avalanche at Ashman (see here). No persistent or deep persistent slab avalanches have been reported since Dec 22.
With more wind and snow in the coming days, natural and human triggered slabs remain a concern.
Snowpack Summary
Strong to extreme wind is moving around 30-50 cm of snow that has fallen since New Year's Day. Thick wind slabs can be found in exposed open terrain while sheltered terrain should have mostly low density snow with some isolated storm slabs potentially forming. Be cautious on steep rolls in sheltered areas where the recent snow may be sitting above weak surface hoar.
The lower snowpack has two crusts that potentially have weak snow around them. One is 60-90 cm below the surface and the other is near the ground. These weak layers produce avalanches on Dec 21 and 22, but since then have been trending towards dormancy. We are uncertain about how likely it is to trigger avalanches on these deeper layers, but would be suspect of shallow rocky alpine slopes.
Terrain and Travel
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
- Choose slopes that are well supported and have limited consequence.
- Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.
Avalanche Problems
Wind Slabs
Intense wind from the southwest will form touchy wind slabs in leeward terrain on Tuesday. In sheltered areas storm snow may also form isolated slabs.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1 - 2
Persistent Slabs
Triggering large avalanches on weaknesses in the lower snowpack remains a possibility. In some areas the concern is weak snow around crusts 60 to 90 cm deep, while in others it is weak snow near the bottom of the snowpack. This problem is best managed by avoiding steep rocky slopes and approaching challenging and complex avalanche terrain with extra caution.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 2 - 3