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

Regions

Sea To Sky.

The snowpack doesn't respond well to rapid change. The impact of the afternoon sun and warm temperatures could bump up the avalanche danger to HIGH. Watch for signs of instability and be conservative with your terrain selection.

Confidence

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

Weather Forecast

Wednesday: Sunny with some cloudy periods. Ridgetop winds 15-25/h km from the south and alpine temperatures + 9 degrees. Freezing levels 3500 m.

Thursday: A mix of sun and cloud. Ridgetop winds 10-20 km/hr from the southwest and alpine temperatures near + 4 degrees. Freezing levels 3000 m.

Friday: A mix of sun and cloud. Ridgetop winds 15-30 km/hr from the southwest and alpine temperatures + 5 degrees. Freezing levels 3000 m.

Avalanche Summary

On Tuesday afternoon numerous size 1-1.5 wet loose avalanches from steep south aspects were reported. A large natural avalanche size 2-2.5 from a north-facing alpine slope was also reported and likely occurred Monday night. 

On Monday explosive triggered storm and wind slab avalanches were reported up to size 2.5. Crown depths generally ranged 20-50 cm, with a 120 cm deep crown observed in a heavily wind loaded feature.

Our eyes and ears in the mountains are limited at this time of year and may continue this winter due to fewer professional observations. If you see anything (or don't) while out in the field, please consider sharing via the Mountain Information Network (MIN). Photos are especially helpful! Thank you so much for all the great MINs submitted so far!

Snowpack Summary

Up to 25 cm of recent snow sits over a thin melt-freeze crust on south aspects and surface hoar in wind-sheltered areas around treeline. Fat pockets of wind loaded snow may be found in leeward features at upper elevations. Forecast sun and rising freezing levels into the alpine will have the greatest impact on the upper snowpack, showing signs of instability. and also promoting slab development.

The snowpack depth varies substantially with elevation. Below treeline 30 to 70 cm, 80 to 100 cm near treeline, and around 150 cm may be found in the alpine.

The mid to lower snowpack contains a series of crusts, the most notable of which is also the deepest, sitting just above the ground at elevations above 1500 m. This crust may have a thin overlying layer of weak faceted grains and/or surface hoar crystals, especially in sheltered areas around treeline. There is uncertainty as to whether these layer will be a concern going forward. 

Terrain and Travel

  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
  • Be cautious of buried obstacles especially below treeline.

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.

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.