Avalanche Forecast

Issued: Dec 22nd, 2017 5:01PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

cgarritty, Avalanche Canada

Purcells.

Where there is uncertainty in the snowpack, conservative terrain is the answer. Check out todays Forecasters blog for tips on managing the spatial variability associated with our current persistent slab problem. LINK

Summary

Confidence

Moderate -

Weather Forecast

Saturday: A mix of sun and cloud. Light to moderate northwest winds. Alpine temperature of -17.Sunday: Mainly sunny. Light southwest winds. Alpine temperature of -15.Monday: A mix of sun and cloud. Light variable winds. Alpine temperature of -17.

Avalanche Summary

Reports from the past few days showed a few size 1-1.5 remote triggered (triggered from a distance) avalanches in the alpine and at treeline. Additional reports showed natural wind and storm slab avalanches to size 2 in the alpine on north and east aspects in the alpine along with skier triggered and natural size 1 loose snow avalanches in steep terrain at tree line and in the alpine. Explosives were the primary trigger for Thursday's activity. Slab avalanche activity can be expected to persist or possibly increase as our recent snow consolidates into a slab above the range of weak surfaces present at the December 15 interface. In areas where new snow has not yet consolidated into a slab, expect continued potential for triggering loose dry avalanches in steep terrain.

Snowpack Summary

Stormy weather over the past week has brought 30-50cm of new snow top the region. The new snow lies over a wide variety of old surfaces, including large surface hoar (weak, feather-like crystals), hard crusts formed by sun or wind, and sugary facets. The bond at this old snow interface becomes critical as the overlying snow gradually consolidates into a slab. The most concerning areas areas will be those that have seen previous surface hoar development, such as sheltered areas at and below tree line and sheltered northerly aspects in the alpine. A crust which was formed by rain in late November is a major feature in the snowpack and is down approximately 60-100cm at tree line elevations. Snowpack tests suggest the snow above is currently bonding well to it.Snowpack depth decreases rapidly below tree line. Look out for early season hazards such as rocks, stumps, and open creeks.

Problems

Wind Slabs

Shifting winds since the storm have been redistributing new snow into wind slabs on a variety of aspects. The most recent of these are the result of Friday's north to northeast winds. Keep this reverse loading pattern in mind as you gain elevation.

Be aware of areas that have been reverse loaded by windsTravel on ridges and/or ribs to avoid wind loaded slopes belowBe cautious as you transition into wind affected terrain.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

Reactivity at the buried December 15 interface will likely be greater where the new snow has settled into a cohesive slab above buried surface hoar. Use extra caution in wind affected areas and around steeper, sheltered slopes at treeline and below.

Buried surface hoar may be preserved on open slopes and convex rolls at and below tree lineWatch for signs of instability such as whumpfing, or cracking. Be aware of increased danger in areas that received greater new snow accumulations.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Dec 23rd, 2017 2:00PM