Archived

Avalanche Forecast

Mar 12th, 2017–Mar 13th, 2017

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

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

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Northwest Inland.

Warm stormy weather will elevate the danger on Monday. Very conservative terrain choices or professional-level training are recommended for any travel in avalanche terrain.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY NIGHT: Storm continues with another 10-15 cm of snow, strong southwest winds, and climbing freezing levels.MONDAY: Another 2-5 cm during the day, strong southwest winds, freezing levels climb to about 1000 m with alpine temperatures around -2 C .TUESDAY: The next pulse brings 5-15 cm starting late Monday night, moderate southwest winds, freezing level dropping with alpine temperatures around -6 C.WENDESDAY: Lingering flurries with 2-5 cm, moderate southwest winds, alpine temperatures around -10 C.

Avalanche Summary

A MIN report from Friday describes a size 1 wind slab avalanche at Hudson Bay Mountain (here). A natural size 2 wind slab was also reported on a northeast aspect in the Howsons.On Monday, the new snow is expected to form reactive storm slabs and has the potential to awake persistent slabs above the weak February interface.

Snowpack Summary

Storm snow totals may reach 20-40 cm by Monday morning with deeper deposits in lee terrain. Rising temperatures will make reactive storms slabs. A weak interface that was buried in late February may finally have enough snow above it to form a reactive slab. The interface is composed of facets, crusts, and surface hoar that may be 40-80 cm deep. There's some uncertainty about the distribution and reactivity of this interface. A well consolidated mid-pack sits above weak basal facets (sugary snow) near the ground. The deeper basal weakness remain a concern in thin rocky start zones and shallow snowpack locations.

Avalanche Problems

Storm Slabs

20-40 cm of new snow will form fresh storm slabs that will be thicker, stiffer, and more reactive in wind affected terrain.

Minimize exposure during periods of heavy loading from new snow and wind.Avoid open slopes with any steepness over 30 degrees.Stick to simple terrain and be aware of what is above you at all times.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Persistent Slabs

A reactive slab has possibly formed above a weak layer of crusts, facets, and surface hoar that formed in February.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Stick to simple terrain and be aware of what is above you at all times.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 2

Deep Persistent Slabs

A lingering weakness at the bottom of the snowpack may reawaken with the load of the new snow and warming.

Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3