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Avalanche Forecast

Archived

Feb 21st, 2018–Feb 22nd, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

Watch for wind slabs and cornices at upper elevations. Keep in mind that the possibility of a large avalanche on a deep weak layer still exists and choose terrain carefully.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY: Mix of sun and cloud. Ridge wind light, northeast. Temperature -15. Freezing level valley bottom.FRIDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, southwest. Temperature -12. Freezing level valley bottom.SATURDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind light, west. Temperature -10. Freezing level valley bottom.

Avalanche Summary

Tuesday there were reports of a skier triggered size 2-2.5 cornice failure that produced very large, bus-sized cornice chunks on an north aspect at 2400m. As well as a size 1.5 natural wind slab failure (50-70 cm deep) on a west aspect at 2050 m.On Monday we received reports of a cornice triggered size 2.5 slab avalanche on a high north east alpine face near 2900m. We also received reports of natural wind slabs to size 2.5 (most crowns 20-40cm thick) on a wide range of aspects above 1900m elevation. On Sunday, several natural wind slab avalanches to size 2 were reported on primarily east aspects between 2200m and 2600m.Also on Sunday, skiers were able to intentionally trigger small (size 1) wind slab avalanches in immediate down wind (lee) features near ridge crests. See here for an update on conditions near Golden. Although deeper, persistent avalanche activity has become less frequent over the past week, light triggers in shallow rocky areas, as well as large triggers such as a cornice collapse or step down from a wind slab release, still have the potential to result in large destructive avalanches.

Snowpack Summary

Recent storm snow totals are 15-30 cm with more in the very south of the region near Kimberley, where totals are closer to 50 cm. Moderate south west through north west winds have redistributed these accumulations into deeper, reactive slabs in wind-exposed terrain. The recent snow sits on the old interface that was buried mid-February consisting of; a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, and surface hoar on sheltered slopes.Below the snow surface several persistent weak layers make up a complex snowpack which is slowly beginning to show sign of improving but still remains suspect. In the top 1-2 m of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below tree line.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.