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Avalanche Forecast

Archived

Feb 1st, 2022–Feb 2nd, 2022

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

Regions

Lizard-Flathead.

Treat open slopes at treeline and below as suspect, new snow sits on a weak surface hoar layer. Watch for signs of instability like shooting cracks and whumpfing.

Wind slabs will continue to form at higher elevations as westerly winds strengthen..

Confidence

High - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Arctic air brings cold temperatures, wind and little chance of snow until Friday.

TUESDAY: NIGHT: Cloudy with clear breaks. Moderate E winds. Freezing level at valley bottom. Isolated flurries

WEDNESDAY: A mix of sun and cloud. Moderate W winds. Freezing level at valley bottom. Alpine high of -18.

THURSDAY: Cloudy with sunny breaks. Moderate W winds. Freezing level at valley bottom. Alpine high -9. 

FRIDAY: Cloudy with flurries, up to 7cm. Moderate SW winds, gusting strong. Freezing level 1000 m, alpine high of -5. 

Avalanche Summary

On Monday a natural cycle was observed to size 2.5 in many areas. Ski cutting and explosive control work also produced slab avalanches to size 2. A vehicle remotely triggered a size 1.5 slab avalanche, indicating sensitivity of the buried surface hoar layer. 

A MIN report noted shooting cracks and whumpfing during their travel, showing reactivity of the January 18 crust (30-50cm) deep and the most recent surface hoar (20-30cm) deep).

A size 2.5 natural persistent slab avalanche was reported to have occurred on a path that had previously avalanched and reloaded bed the surface.

Snowpack Summary

At lower elevations up to 30cm of storm snow sits over a thick melt freeze crust. In sheltered terrain, a widespread layer of surface hoar sits immediately above the crust, typically 10-20 mm but as big as 30 mm in places. 

At higher elevations the storm snow is being redistributed by moderate to strong northwest winds, over a snow surface that was previously heavily wind affected. A thin melt freeze crust extends into the alpine on solar aspects. This crust may sit on the surface or below wind deposited snow. 

The widespread January 18 rain crust is now down around 40-50 cm but has not been producing avalanches recently. 

The mid snowpack is strong and well-consolidated above the early December facet/crust layer which is now down 100-200 cm. This layer has been dormant recently and is not currently a concern for the region but could still be a problem in the future. See the most recent forecaster blog for more details on this layer. 

Terrain and Travel

  • Be especially cautious as you transition into wind affected terrain.
  • Wind slabs may be poorly bonded to the underlying crust.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.

Problems

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.

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.