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Avalanche Forecast

Archived

Dec 1st, 2020–Dec 2nd, 2020

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

Regions

Northwest Inland.

We're going from cold and stormy to unseasonably warm and sunny in quite a hurry which is expected to de-stabilize our snowpack. Cornice failures and very large natural avalanches are possible as we head into the warm spell.  

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday looks to be warm right up into the alpine. Temperatures return to more seasonal norms Thursday and Friday with a chance for a bit of fresh snow Saturday.

TUESDAY NIGHT: Freezing level between 2500 and 3000 m through the night, strong to extreme southwest wind, 1 to 5 cm of snow possible at ridge top with rain falling at most elevations.  

WEDNESDAY: Mostly clear skies through the bulk of the day with cloud cover increasing after sunset, freezing level holding between 2500 and 3000 m, strong to extreme southwest wind, no precipitation expected.

THURSDAY: Broken cloud cover, freezing level between 500 and 700 m, moderate to strong southwest wind, 1 to 5 cm of snow.

FRIDAY: Broken cloud cover, freezing level at or near valley bottom, moderate to strong southwest wind, up to 5 cm of snow possible.  

Avalanche Summary

Observations are very limited but the combination of snow and wind over the past few days has almost certainly formed wind slabs in open terrain. 

Please submit your observations to the Mountain Information Network!

Snowpack Summary

The storm produced about 15 to 50 cm of new snow with areas in the far north of the region receiving the bulk of the precipitation. The wind effect is thought to be extensive. See this MIN from a few days ago which does a great job of showing the effect of the wind.

Heavy wind effect seems to be the theme from last week, and that is expected to continue into this week.

Snowpack depths range from 60 cm in eastern parts of the region up to over 100 cm in western parts of the region. Lower elevation terrain may still be below the threshold for avalanches. Reports suggest the bottom half of the snowpack consists of crusts, and in some cases weak snow may be developing around these crusts. This will be a layer to monitor as the season progresses.

Terrain and Travel

  • Avoid all avalanche terrain during periods of intense solar radiation.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Avoid exposure to slopes that have cornices overhead.
  • Avoid freshly wind loaded terrain features.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.