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Archived

Avalanche Forecast

Feb 19th, 2013–Feb 20th, 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
3: Considerable
The avalanche danger rating below treeline will be considerable
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
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.

Tricky conditions persist due to a weak layer in the top 50 cm of the snowpack.  This layer is widespread, but is more reactive in specific terrain features.  Careful evaluation is required.  Watch for large cornices, and warming during sunny breaks.

Weather Forecast

An upper trough will pass through the area today, maintaining overcast skies and a chance of flurries.  Temperatures remain mild with light NE winds shifting to SW.  On Wednesday, a ridge of high pressure will move in bringing clearing skies and sunshine.  Another front will move in on Thursday.

Snowpack Summary

Hard and Soft slabs overly a weak layer of surface hoar, now buried 50-60cm.  This surface hoar is best preserved and reactive between 17-1900m, and is most reactive on solar aspects where it rests on a buried sun crust.  RB scores of 2 (whole block), and wide avalanche propagations confirm that this layer is becoming touchier as it matures.

Avalanche Summary

In the park, avalanches to size 3, including one glide avalanche, were observed along the highway corridor.  One avalanche was observed below lookout col, shallow (30cm), but very wide propagation.  Several loose snow slides were noted on solar aspects.  Near neighbors have reported many avalanches on the Feb. 12 surface hoar layer. 

Confidence

Due to the number of field observations

Avalanche Problems

Persistent Slabs

The Feb 12 PWL is becoming more reactive as it matures.  Skier triggered and natural avalanches have been increasing on this layer, with RB scores of 2, whole block.  It is most reactive on solar aspects between 17-1900m.
Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.Choose well supported terrain without convexities.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Wind Slabs

Soft windslabs formed on the immediate lees of ridges above treeline. In wind-affected areas the recent storm snow will be more cohesive. These slabs overlay a touchy surface hoar layer and if triggered, avalanches may propagate widely.
Avoid freshly wind loaded features.Be aware of the potential for wide propagations due to the presence of hard windslabs.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2