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Avalanche Forecast

Archived

Nov 24th, 2019–Nov 25th, 2019

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

Regions

Purcells.

Strong westerly wind combined with up to 20 cm of new snow has likely formed storm slabs which will be most problematic near ridge crest. The weak & highly variable snowpack likley needs time to adjust. Conservative terrain selection is prudent Monday.

Confidence

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

Weather Forecast

After a stormy weekend we’re transitioning to clearing skies, colder temperatures and no significant precipitation for the foreseeable future.

SUNDAY NIGHT: Freezing level dropping to valley bottom, light west/northwest wind, trace of snow possible.

MONDAY: Broken cloud cover, freezing level at valley bottom, light NW breeze, no significant precipitation expected.

TUESDAY: Scattered cloud cover, freezing level at valley bottom, light variable breeze, no significant precipitation expected.

WEDNESDAY: Broken cloud cover, freezing level at valley bottom, moderate east wind, no significant precipitation expected.

Avalanche Summary

We received a report of a skier controlled avalanche on a north facing alpine feature in the central portion of the region late Sunday. The size 2 wind slab avalanche was about 20 cm deep. Other than that, no recent avalanche activity has been reported. There may have been a natural avalanche cycle Saturday night into Sunday in the northern portion of the region. If you were out this weekend please let us know what you were seeing on the MIN! 

Snowpack Summary

Winter is slowly creeping down to the valley. Snowpack depths range from about 10 to 120 cm. The weekend storm produced 10 to 20 cm of snow accompanied by strong west, southwest & northwest wind. Storm snow accumulations are greatest in the north of the region. 

The young snowpack is highly variable due to previous wind transport and areas of shallow snow which are highly faceted. Most treeline and below treeline areas are probably below threshold for avalanches at this time. A potentially problematic melt freeze crust from late October can be found above basal facets in the lower snowpack. There's a great "pre-weekend-storm" summary of current conditions in the Golden area here.

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.