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Archived

Avalanche Forecast

Feb 24th, 2013–Feb 25th, 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
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
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
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Glacier.

Slab overtop buried surface hoar is producing less frequent but larger avalanches at lower elevations and wind slabs are the main concern up high.

Weather Forecast

Westerly flow bringing light amounts of snow today. Pacific frontal system arriving to the region  this evening, expecting moderate amounts overnight with associated strong west winds. Lingering flurries on Monday and dry conditions are forecast for Tuesday.

Snowpack Summary

Top 30cm low density snow. Localized Feb 15 drizzle crust down 20-30cm. Feb 12 surface hoar(SH)/crust layer is down 40-50cm. Fracture line profile on size 2.0 avalanche, Mt Fidelity, showed the Feb 12 bed surface layer as SH size 3-7 on a 3cm crust. Moderate sudden planar compression test results and a Rutschblock 3 whole block on that layer.

Avalanche Summary

From yesterday: 5 natural slab avalanches ranging in size 2 to 2.5 east of the Rogers Pass summit.From Feb 22: Skier controlled size 2.0 slab avalanche on Mt-Fidelity, 33-40deg, south aspect, down 35-45cm, 1700m, 100m wide, 120m long

Confidence

Due to the number of field observations on Sunday

Avalanche Problems

Persistent Slabs

A buried surface hoar layer, down 40-50cm, reactive to skier triggering particularly where it sits on a crust on steep south aspects. The overlying slab is stiffening and will produce larger propagation avalanches when triggered.
Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3

Wind Slabs

Moderate to strong overnight winds with new snow available to be moved by it has created wind slab at the higher elevations. Evidence of wind affect was also seen in open areas below tree line.
Avoid freshly wind loaded features.Be cautious as you transition into wind affected terrain.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2