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Avalanche Forecast

Archived

Nov 30th, 2020–Dec 1st, 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, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Lizard-Flathead.

Wind slabs on leeward slopes may be reactive to human triggering, especially in steep unsupported terrain features. The afternoon sun may have enough punch to weaken snow surfaces, especially on steep south slopes. Heads up for changing conditions.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

High pressure builds off the coast on Tuesday bringing a mix of sun and cloud. Wednesday afternoon may see a temperature inversion above 2000 m.

Monday Night: Light snow expected up to 5 cm. Strong WNW winds in the alpine. 

Tuesday: Mix of sun and cloud. Alpine temperatures near -2. Strong ridgetop winds from the WNW. Possible Alpine temperature inversion bringing warm air above 2000 m.

Wednesday: Mostly cloudy with some sun. Alpine temperatures near 0 degrees or warmer if the inversion is strong. Ridgetop winds light from the East.

Thursday: Mix of sun and cloud. Alpine temperatures near -2. Ridgetop winds light from the southwest.

Avalanche Summary

Observations are limited right now, but there have been no reports of recent avalanches. We appreciate the recent reports submitted to the Mountain Information Network. Keep them coming!

Snowpack Summary

Wind slabs have formed in open terrain as last weeks 10 to 20 cm of snow is redistributed and formed into more cohesive slabs. These slabs may sit above a layer of surface hoar in sheltered terrain and above a hard crust in other areas.

Surface snow conditions may change with forecast sunshine and warmer temperatures up high on Tuesday afternoon and Wednesday. Surface snow may be moist and reactive on sunny slopes then re-freeze overnight into a crust.  

Snowpack depths at upper treeline elevations are nearing 100 cm and beginning to exceed the threshold for avalanches, while the snowpack is much thinner in the valleys. 

The lower snowpack consists of crusts. Weak snow may be developing around these crusts in some areas, which will be a snowpack feature to monitor as the season progresses.

Terrain and Travel

  • Avoid areas where the snow feels stiff and/or slabby.
  • Avoid freshly wind loaded terrain features.
  • Be alert to conditions that change with elevation and sun exposure.

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.