Avalanche Forecast
Issued: Dec 20th, 2017 3:50PM
The alpine rating is Wind Slabs and Deep Persistent Slabs.
, the treeline rating is , and the below treeline rating is Known problems includeCool and stable weather should mean a gradually strengthening snowpack, but take note of shifting winds.
Summary
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.
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
Expected Size
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
Expected Size
Valid until: Dec 21st, 2017 2:00PM