Archived

Avalanche Forecast

Mar 13th, 2017–Mar 14th, 2017

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

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 weather has opened the door for large avalanches on deep weak layers. It's time to be extra conservative with your terrain choices.

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

TUESDAY: Another storm with 5-15 cm of new snow, strong southwest winds, freezing level dropping with alpine temperatures around -4 C.WENDESDAY: Lingering flurries with 2-5 cm, moderate southwest winds, alpine temperatures around -8 C.THURSDAY: Scattered clouds with isolated flurries, moderate southwest winds, alpine temperatures around -8 C.

Avalanche Summary

Small avalanches have been reported in wind affected terrain the past few days, including a few naturals up to size 2 and a few size 1-1.5 skier-triggered avalanches. A MIN report from Friday describes a size 1 wind slab avalanche at Hudson Bay Mountain (here).The storm snow is expected to form reactive slabs and has the potential to form a persistent slab above the weak February interface.

Snowpack Summary

Another 5-15 cm and strong winds will continue to build storm slabs after Sunday's storm delivered 15-30 cm. Warm temperatures will make touchy slabs at higher elevations and unstable wet snow at lower elevations. 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 and may be 40-80 cm deep. There's uncertainty about the distribution and reactivity of this interface. The mid-pack is well consolidated and sits above weak 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

Another storm pulse will develop thicker storms slabs that will be extra reactive in the lee of exposed terrain.

Minimize exposure during periods of heavy loading from new snow and wind.Use conservative route selection, stick to moderate angled terrain with low consequence.

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.

Choose well supported terrain without convexities.Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 2 - 3

Deep Persistent Slabs

A lingering weakness at the bottom of the snowpack may reawaken with the load of the new snow and warming. It'll be most reactive in thin rocky start zones and shallow snowpack locations.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3