Avalanche Forecast

Issued: Mar 13th, 2017 3:32PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs, Persistent Slabs and Deep Persistent Slabs.

shorton, Avalanche Canada

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.

Summary

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.

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

Valid until: Mar 14th, 2017 2:00PM