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Avalanche Forecast

Archived

Nov 28th, 2020–Nov 29th, 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, 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

Glacier.

High quality skiing and riding has been found this week. Continue to choose your routes carefully and test for triggerability before dropping in. Large natural avalanches have been running to valley bottom

Weather Forecast

A brief ridge of high pressure is forecast to bring clear spells and high temperatures of -9 today and -5 and cloudy tomorrow. A cold front is due to pass through on Monday bringing another 10cm of snow, falling freezing levels and strong SW wind.

Snowpack Summary

An additional 15cm overnight now makes 60 cm of storm snow over old snow and the Nov 23 surface hoar size 3. The surface hoar has been observed at treeline in isolated areas but in some other profiles has not been found. The Nov 5 crust is now between 90 and 140cm down which is within the triggerable range for skiers and snowboarders in some areas.

Avalanche Summary

3 large natural avalanches were detected early this morning by IDA. A skier triggered sz 1.5 on surface hoar in Avalanche Crest yesterday was reported using MIN. A sz 2.5 on Thursday also failing on SH with wide propagation was reported from just outside the park. Numerous new natural slides in the HWY corridor this week mostly sz 2 with a few sz3s

Confidence

Due to the number of field observations

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.

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.