Avalanche Forecast
Issued: Mar 1st, 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
A weak layer has reared its head as the overlying slab has matured. Human triggered avalanches are very likely. Keep in mind it's not always the first rider who triggers the slab.
Summary
Confidence
High -
Weather Forecast
Sunday night: Increasing cloud and isolated flurries. Moderate to strong northwest wind, extreme at ridgetop by early morning. Freezing level 800 m.
Monday: Flurries bringing up to 5 cm new snow. Moderate west wind, strong at ridgetop. Freezing level 1300 m.
Tuesday: 10-15 cm new snow overnight, clearing. Mix of sun and cloud. Moderate west wind. Freezing level 1700 m.
Wednesday: 10-20 cm new snow. Moderate northwest wind. Freezing level 1200 m.
Avalanche Summary
Friday and Saturday saw a surge in persistent slab avalanche activity on the February 22 surface hoar layer. Numerous skier triggered and remote triggered size 1-1.5 were reported by nearly every ski operation region wide even as professionals seek to actively avoid suspect terrain features. In a few instances, slopes were ski cut with no results, only to have the third or fourth skier in the group accidentally trigger the slab. Extensive propagation was showing connectivity between terrain features that normally do not avalanche concurrently, as well as between treewells in forested areas. Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline.
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.
Snowpack Summary
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). Uncertainty exists around distribution of the surface hoar, but it has been associated with avalanche activity on all aspects and elevations. Read more about surface hoar on our forecaster blog!
The mid and lower snowpack is well settled and strong.
Terrain and Travel
- 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.
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Avoid steep convex slopes.
- Choose slopes that are well supported and have limited consequence.
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).
Skier triggering of these persistent slabs is very likely, and has be 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 is forecast to pick up again on Monday, and resume windslab development in the alpine and exposed treeline elevations. Expect reactive wind slabs in lee terrain features such as just below ridgetop and on convexities.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 2nd, 2020 5:00PM
