Avalanche Forecast

Issued: Nov 27th, 2015 8:29AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Loose Wet, Wind Slabs and Deep Persistent Slabs.

bcorrigan, Avalanche Canada

South Columbia.

Rising temperatures in the alpine may change the snowpack dramatically, especially on solar aspects. Forecasters are working with little information this early in the season. Share your observations through the Mountain Information Network. MIN

Summary

Confidence

Fair - Due to the number and quality of field observations

Weather Forecast

An arctic high continues to dominate the weather pattern over western Canada and is not forecast to move out of the area until Tuesday or Wednesday next week. In the meantime, an above-freezing layer (AFL) of air will pass through the region between 1500 and 3000m bringing temperatures in that elevation band to as high as +5°c., especially on solar aspects. Arctic air pooling in the valley bottoms will keep the temperatures well below freezing until the next storm system flushes out the cold air

Avalanche Summary

We've received a few reports of avalanche activity from operators that include relatively large (size 2.5) avalanches triggered by explosives, as well as a number of large natural avalanche that happened a few days days ago. Yesterday there were reports of small-loose avalanches believed to have run on the Nov 23rd surface hoar.

Snowpack Summary

The snowpack has been described by some observers as "extremely variable", with wind effect in all open alpine areas from the Northerly winds after the last storm. Surface hoar is widespread and observed to 4mm in sheltered locations, while windward slopes have been scoured down to bare rock in other places. Cold arctic air and temps down to -20 in some areas are promoting surface facetting. The above-freezing-layer now passing through the region could dramatically alter the snowpack.

Problems

Loose Wet

Rising temperatures on solar aspects may trigger "snowballing" in steep alpine terrain, with the possibility of loose wet avalanches being triggered at treeline as well

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Be careful with wind loaded pockets while approaching and climbing ice routes.>

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Wind Slabs

Wind slabs are still lurking out there, in places you might not expect them. Reverse loading from northerly winds have built slabs on south aspects .

Use ridges or ribs to avoid pockets of wind loaded snow.>Avoid freshly wind loaded features.>Be cautious as you transition out of wind sheltered terrain.>The new snow will require several days to settle and stabilize.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

There is concern about the potential to trigger a deep instability in shallow snowpack areas that may have facetted snow from earlier in the season. Mostly on northerly aspects.

Be aware of thin areas that may propogate to deeper instabilites.>Now is a good time to dig a snow profile (or two) and figure out how the snowpack changes with aspect and elevation.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

2 - 5

Valid until: Nov 28th, 2015 2:00PM