Avalanche Forecast
Issued: Mar 2nd, 2020 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
It's spicy out there right now. Between fresh wind slabs and a touchy persistent weak layer, human triggered avalanches are very likely. Keep in mind it's not always the first rider who triggers the slab.
Summary
Confidence
Weather Forecast
Monday night: 5-10 cm new snow. Moderate west wind, strong at ridgetop. Freezing level 1300 m.
Tuesday: Mix of sun and cloud, flurries starting in the evening. Moderate west wind. Freezing level 1500 m.
Wednesday: 5-15 cm new snow. Light to moderate northwest wind. Freezing level 1200 m.
Thursday: Up to 5 cm new snow. Light to moderate southwest wind. Freezing level 1600 m.
Avalanche Summary
Friday, Saturday and Sunday saw a surge in persistent slab avalanche activity on the February 22 surface hoar layer. Numerous skier triggered and remote triggered size 1-2 were reported by nearly every ski operation region wide even as professionals seek to actively avoid suspect terrain features. Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline.
In several instances, slopes were ski cut with no results, only to have the third or fourth skier in the group accidentally trigger the slab. In other cases, avalanches were triggered on slopes with old ski tracks or where avalanches had already released.
Naturals triggered by cornice falls, loose snow running out of extreme terrain or warming temperatures were observed mostly around size 2, but up to size 3. Natural wind slab avalanches size 1-2.5 were observed on easterly aspects in the alpine on Sunday.
Snowpack Summary
Light snowfall and strong winds are building fresh wind slabs in the alpine and open areas at treeline.
A weak layer of widespread surface hoar sits 40-70 cm deep, ontop of a crust on solar aspects. The overlying snow has been cohered into slabs by incremental loading through successive storms, wind and mild temperatures. As slab character and depth increase, so do reactivity and size of avalanches failing on the weak layer. Read more about surface hoar on our forecaster blog!
The mid and lower snowpack is well settled and strong.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Even brief periods of direct sun could produce natural avalanches.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
- Surface hoar distribution is highly variable. Avoid generalizing your observations.
- Avoid steep convex slopes.
Problems
Persistent Slabs
A weak layer of surface hoar sits 30-60 cm deep. The overlying snow has been cohered into slabs by incremental loading through successive storms, wind at upper elevations and mild temperatures at lower elevations. As slab character increases, so do reactivity and size of avalanches failing on the weak layer (surface hoar). Read more about surface hoar on our forecaster blog!
Human triggering of these persistent slabs is very likely, and has been observed extensively through the region over the last few days even as professionals seek to actively avoid suspect terrain features (eg. convex rolls). Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Wind slab development continues in the alpine and exposed treeline elevations. Expect reactive wind slabs in lee terrain features such as just below ridgetop and on convexities. If triggered, windslabs have the potential to trigger deeper weak layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 3rd, 2020 5:00PM
