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Archived

Avalanche Forecast

Mar 20th, 2013–Mar 21st, 2013
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Glacier.

Cornices are large and unsupported.  A few have failed recently, causing large avalanches.  The new storm snow will be a concern everywhere, however solar aspects are most problematic due to buried sun crusts.

Weather Forecast

A low will bring increasing precipitation today, with most intense accumulations occurring mid-day.  Upslope (westerly) locations will receive locally heavy amounts, accompanied by strong southerly winds.  Freezing levels will rise to 1300 m today, and drop tomorrow as a cold front follows.  Unsettled conditions will remain for tomorrow and Friday.

Snowpack Summary

Storm snow slabs exist in the alpine, but are sporadic.  Reports from north aspects (Dome Glacier) indicate the upper snow is well bonded; however avalanches to size 2.5 were observed yesterday from solar aspects in the Connaught drainage.  Where storm slabs rest on a buried suncrust-surface hoar combo (March 11), wide propagations can be expected.

Avalanche Summary

Numerous slabs were seen yesterday, mostly in the top 30-40cm.  Skiers on Mt. Sifton yesterday were able to cut a cornice to check the slope, and released a size 2.5-3 avalanche on a south aspect, 40cm deep x 100m wide.  Another size 2.5-3 slab was seen in the Asulkan drainage on Mt. Abbott. 

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Wednesday

Avalanche Problems

Storm Slabs

Another 8-10cm of snow overnight has added load to last weeks storm interface.  More snow, moderate winds and warm temps today will add to this problem, especially on solar aspects where buried suncrusts are providing good failure planes.
Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Avoid steep slopes below cornices.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 2 - 3

Wind Slabs

Isolated wind slabs in the alpine and near ridge crests surprised a few skiers yesterday.  These failures could break down to deeper instabilities.  Cornices are very large and unsupported.
Be careful with wind loaded pocketsAssess start zones carefully and use safe travel techniques.

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2

Persistent Slabs

It will likely take a large trigger, like a cornice or another avalanche to trigger the surface hoar/crust layer from February 12, now down 1-1.5m. The resulting avalanche would be very large and destructive if triggered.
Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 3 - 4