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 right now. Avoid sharp changes in terrain shape and keep in mind it's not always the first rider who triggers the slab.
Summary
Confidence
Weather Forecast
Sunday night: Flurries bringing up to 5 cm new snow. Moderate to strong northwest wind, extreme at ridgetop by early morning. Freezing level 700 m.
Monday: Flurries bringing up to 5 cm new snow. Moderate west wind, strong at ridgetop. Freezing level 1200 m.
Tuesday: Flurries bringing 5-15 cm new snow. Moderate west wind. Freezing level 1500 m.
Wednesday: 10-25 cm new snow. Moderate west wind. Freezing level 1000 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 1-2 were reported by operators across the region 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. Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline.
Natural size 2-3.5 persistent slabs were also observed, suspect triggers include cornice falls, tree bombs and wind loading.
Snowpack Summary
Recent wind has redistributed surface snow in the alpine and exposed treeline, loading snow into lee terrain features. Fresh wind slabs will continue to form as the wind picks up again Monday.
A weak layer of widespread surface hoar sits 40-70 cm deep. On solar aspects it sits on a sun crust which makes an excellent bed surface for avalanches. 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!
The early-February melt-freeze crust down 50-100 cm is dormant but still on our radar. 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.
- Avoid steep convex slopes.
- Choose slopes that are well supported and have limited consequence.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Problems
Persistent Slabs
A weak layer of surface hoar sits 40-70 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!
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. If triggered, windslabs have the potential to trigger deeper weak layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 2nd, 2020 5:00PM
