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Archived

Avalanche Forecast

Apr 25th, 2013–Apr 26th, 2013
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Glacier.

High winds overnight has likely added to the slab problem, causing the hazard rating in the alpine to be considerable.  Up to 16mm of precipitation for Saturday will also bump up the alpine hazard then.  Otherwise, spring conditions continue.

Weather Forecast

The South Columbia's will be dry due to a ridge of high pressure, while the North will be wetter as a low moves through.  Rogers Pass is on the boundary, so cloud and a chance of convective precipitation is expected.  More unsettled weather is forecasted for the weekend, starting on Friday with the bulk of the rain (up to 16 mm) arriving Saturday.

Snowpack Summary

Variable springtime conditions:  a 10-15cm thick crust on solar aspects and lower elevations overlies near isothermal snowpack which firms up overnight, and looses strength during the warmth of the day.  In the alpine, a mix of hard and soft slab persists, with dry snow on polar aspects.  Lots of variability in snow depth across terrain.

Avalanche Summary

The number of avalanche observations has dropped off, in part due to fewer people in the backcountry to report.  Cornice failures remain the biggest concern for triggering larger slab avalanches, which are mostly failing on the April 3 PWL (sun crust-surface hoar combo), down 40-80cm.  Cloud today will reduce the likelihood of moist avalanches.

Confidence

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

Avalanche Problems

Wind Slabs

Winds up to 60 kph overnight have likely added to the slab problem.  High variability of snow depth across terrain means some areas will be quite loaded, and others very thin.  These slabs have a potential for wide propagations in the right terrain.
Avoid freshly wind loaded features.Be aware of the potential for wide propagations due to the presence of hard windslabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 3

Persistent Slabs

Large avalanches failing on deeper weak layers are still being triggered by skiers/riders. They are also sporadically occurring naturally, triggered by wind loading, cornice fall and solar warming.
Be aware of the potential for full depth avalanches due to deeply buried weak layers.Extra caution needed around cornices with current conditions.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 2 - 3

Loose Wet

Moist sluffs are possible at lower elevations today, although cloud cover may keep things firm well into the day.  High freezing levels (possibly to 2500m) may result in loose-wet sluffs at higher elevations as well.
Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.Avoid slopes with glide cracks.

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

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 2