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Avalanche Forecast

Dec 20th, 2020–Dec 21st, 2020
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
4: High
The avalanche danger rating below treeline will be high
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Lizard-Flathead.

A new storm with intense loading rates is set to hit the region by Monday afternoon and continue overnight. Danger ratings may rise to HIGH by late afternoon. Avoid all avalanche terrain during periods of heavy loading from new snow and wind.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

SUNDAY NIGHT - Early evening flurries, minor accumulations / light to moderate south west wind / low -4

MONDAY DAY - Moderate to heavy accumulations 15-25 cm / moderate south west wind / high of -1 

MONDAY NIGHT - 20-30 cm / gusty south west winds / low of -4

TUESDAY - Cloudy with lingering flurries, light accumulations possible / windy at times / high of -3

WEDNESDAY- Sunny with cloudy periods, high of -5

Avalanche Summary

On Sunday there was extensive natural and explosives triggered avalanche activity up to size 3.

There have also been a few accidentally skier triggered avalanches involving both storm snow and the December crust layer such as this one from the MIN.

 

On Saturday explosives produced results up to size 2 on the early December crust. On Friday there were a few natural size 2 wind slab avalanches reported in the alpine.

Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter!

Snowpack Summary

After a break Sunday night, snow will pick up again on Monday. This continued loading will mean more new reactive storm slabs.

Depending on aspect and elevation 60-100 cm now sits on the early December crust. There is increasing evidence that this persistent weak layer, with facetted crystals and surface hoar crystals above and/or below it are reaching a tipping point. 

Deeper in the snowpack are two hard melt-freeze crusts that formed in November that may have some weak crystals around them. There is uncertainty if and where in the region this may be a problem. 

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Don't let the desire for deep powder pull you into high consequence terrain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Avalanche Problems

Storm Slabs

The snowpack isn't getting much time to adjust to recent snowfall and wind as a new wave of precipitation is set to hit the region Monday afternoon. Simple, low angle terrain away from overhead hazard is a good choice right now.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 2.5

Persistent Slabs

This layer has reached a tipping point. Depending on elevation and aspect, 40-100 cm of snow currently sits above a buried crust from early December. Sugary, facets and surface hoar around the crust mean persistent slabs are likely reactive, especially to human triggers. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1.5 - 3