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Avalanche Forecast

Archived

Nov 27th, 2021–Nov 28th, 2021

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

Regions

Northwest Inland.

Forecast snow and wind will form LARGE touchy storm slabs at treeline and above. These slabs will be especially reactive on leeward features. 

Careful route finding and conservative terrain use will be required to play safe in the mountains on Sunday.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

SATURDAY NIGHT: Snow/rain; 15-20 cm / Extreme, southwesterly winds / Low of -1 / Freezing level rising to 1300 m.

SUNDAY: Snow/rain; 5-15 cm / Extreme, southwesterly winds / High of -1 / Freezing level lowering to 900 m

MONDAY: Mix of sun and cloud with flurries / Moderate, southwesterly winds / High of -7 / Freezing level surface.

TUESDAY: Snow/rain; 10-20 cm / Extreme, southwesterly winds / High of -1 / Freezing level rising to 1200 m.

Avalanche Summary

Recent large, natural storm slab avalanches up to size 3 were reported on west and northwest aspects in the alpine.

Forecast snow and wind are expected to form touchy storm slabs at upper elevations that will be very reactive to human triggers.

Snowpack Summary

Forecast 15-20 cm of new snow and strong southwesterly winds will form reactive storm slabs sitting on a hard crust.

A crust formed in early November has been reported down 100-150 cm. There has been some evidence of large avalanches running on this crust. This will be a layer to monitor throughout the season.

Treeline snow depths are estimated to be 150-200 cm.

Terrain and Travel

  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
  • Avoid all avalanche terrain during periods of heavy snowfall.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Be especially cautious as you transition into wind affected terrain.
  • Remember that the snowpack will be significantly different at higher elevations than lower down.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.