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Avalanche Forecast

Archived

Feb 15th, 2020–Feb 16th, 2020

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

Regions

Purcells.

Large deep persistent slab avalanches continue to be reported in the Purcells. Be extra cautious of large steep alpine slopes, especially those getting hit by the sun.

Confidence

Moderate - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

SATURDAY NIGHT: A weak front crossing the region brings up to 10 cm in the southern Purcells and 5 cm in the northern Purcells, moderate wind with strong gusts from the west, alpine temperatures drop to -10 C.

SUNDAY: Mix of sun and cloud with some isolated flurries, moderate wind from the northwest, alpine high temperatures around -6 C.

MONDAY: Mix of sun and cloud, light wind from the northwest, alpine high temperatures around -8 C.

TUESDAY: Mostly sunny, light wind from the northwest, alpine high temperatures around -8 C.

Avalanche Summary

A few natural size 2 avalanches were reported on east facing wind-loaded slopes on Saturday and a few small (size 1) slabs have been human triggered at treeline and alpine elevations over the past few days.

Large sporadic avalanches continue to be reported every few days. On Thursday, a size 2.5 deep persistent slab avalanche was observed in steep rocky alpine terrain on a southwest slope near Golden (see the MIN report). On Wednesday, a large snowmobile triggered avalanche was reported on a convex roll at treeline at Quartz Creek (see the MIN report). On Monday, two deep persistent avalanches (size 2.5 and 3) were triggered with explosives in the central part of the region, both running on north aspects in the alpine. These isolated large avalanches highlight the importance of careful snowpack and terrain evaluation in the Purcells.

Snowpack Summary

20-50 cm of low density snow has fallen over the past week and has shown some reactivity at higher elevations where it has been redistributed it into wind slabs. This snow sits above a rain crust that extends up to 1600-1900 m. Sun crusts can be found near the surface on steep south-facing slopes. The middle of the snowpack is generally settled but the base of the snowpack contains basal facets. It remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall. 

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.