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Archived

Avalanche Forecast

Dec 20th, 2017–Dec 21st, 2017
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
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Northwest Coastal.

Cool and stable weather should mean a gradually strengthening snowpack, but take note of shifting winds.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Thursday: Flurries in the morning, then clearing. Winds moderate northwesterly becoming light northeasterly. Treeline temperatures around -10C.Friday: Clear and sunny. Easterly outflow winds expecting to increase in valleys that drain towards the ocean. Temperatures around -15C.Saturday: Clear and sunny. Continued easterly low level outflow winds. Temperatures around -17C.

Avalanche Summary

Explosive control work on Tuesday managed to produce some large avalanches that failed on the crust buried at the end of October on north through east aspect alpine slopes in the Stewart area. A natural storm avalanche cycle was observed last weekend up to size 2.5. Colder weather is most likely to reduce the amount of avalanche activity in the coming days.

Snowpack Summary

The region picked up 20 to 60cm of storm snow last weekend accompanied by winds out of the southwest, west, northwest, and most recently the east. Since then, little additional snow has fallen, but cooler temperatures have kept snow dry and susceptible to being blown around by the wind. Wind slabs may rest on a melt freeze crust (reported to be 3 to 15cm thick), and there are reports there also may be surface hoar resting above this crust in sheltered locations. Below this crust the mid-pack is reported to be generally strong. You can expect to find a second prominent crust, which was buried at the end of October, 100 to 200cm below the surface. This lower layer may have associated facets, particularly in more shallow locations.

Avalanche Problems

Wind Slabs

20 to 60cm of snow fell during the weekend with wind from the SW, W, NW and SE. As a result, wind slabs on a wide variety of aspects should be expected.
Be alert to conditions that change with elevation, aspect and exposure to wind.Watch for signs of instability such as whumpfing or cracking.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 3

Deep Persistent Slabs

This problem appears to be ongoing, particularly in areas around Stewart and to the north. Likely trigger points are in steep, rocky alpine terrain.
Minimize exposure to overhead avalanche terrain, carefully select genuinely safe spots to re-group.Storm slabs in motion could step down and trigger deep persistent slab avalanches.Be especially cautious in areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3