New snow, wind and mild alpine temperatures are increasing danger ratings. Now is the time for very conservative terrain choices and avoiding exposure to overhead avalanche hazard. The potential for large avalanches to run long distances exists.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
TONIGHT: Snow. Accumulation 10-15 cm. Ridge wind light, north. Temperature -5. Freezing level 300 m.THURSDAY: Mix of sun and cloud, light flurries. Accumulation up to 2 cm. Ridge wind light, northeast. Temperature -6. Freezing level valley bottom.FRIDAY: Mostly sunny. Ridge wind light, northeast. Temperature -8. Freezing level valley bottom.SATURDAY: Mostly cloudy. Ridge wind light, south. Temperature -5. Freezing level valley bottom.
Avalanche Summary
Tuesday there were reports of two skier triggered size 1 wind slab releases just northwest of Terrace, where a soft slab up to 35 cm deep had formed on wind-loaded features.Monday evidence of a natural avalanche cycle from size 2.5 - 3.5 was reported on north to south aspects between 1000-1700 m, west of Terrace, with several persistent slabs suspected to have failed on the mid or early January layers during the height of the weekend's storm.Sunday north of Meziadin Junction a natural size 4 and a natural size 3.5 were observed on a southwest and northeast aspect at 1800-2000 m and are suspected to have failed on the mid-January layer.On Saturday wind and storm slab avalanches failed naturally to size 2 on a variety of aspects in both alpine and treeline elevation bands. A natural size 3 persistent slab avalanche was observed on a steep north facing alpine feature with a crown up to 100 cm in depth, which suggests the mid-January interface was involved. A another very large avalanche (size 3.5) was reported from an unknown aspect/elevation.
Snowpack Summary
Wednesday's storm delivered another 20-30 cm of new snow during the day, and a mix of rain and freezing rain for areas west of Terrace, bringing storm snow totals of over 100 cm in the last 10 or 12 days.Beneath the storm snow lies a 5-20 cm thick crust that was buried early February and can be found 40-90 cm below the surface on all aspects up to 1400 m. A weak layer buried in mid-January is 120-150 cm below the surface and remains a concern. In most areas this layer is a crust, but it may also be surface hoar in sheltered areas at treeline and below. This layer produced a few human triggered avalanches throughout the region over the past week, and may remain reactive as it adjusts to the weight of the new snow.In thinner snowpack areas (north and inland), deeper crust / surface hoar layers that were buried in December and early January may still be a concern. They are buried over 150 cm below the surface, but may be triggerable from shallow spots.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.