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Avalanche Forecast

Archived

Dec 23rd, 2022–Dec 24th, 2022

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Glacier.

Minor weather inputs Friday were enough to overload our frail and fragile snowpack. With heavy snowfall, strong winds and rapid warming in the forecast, Saturday will be a good day to stick to conservative terrain, and minimize overhead hazard.

Confidence

High

Avalanche Summary

An avalanche cycle has begun, with numerous loose dry and thin storm slab avalanches observed in the highway corridor on Friday. These were mostly in the size 1.5-2.5 range, with one notable size 3.0 out of the Lens path on the south side of Mt. Tupper.

A field team in the Fidelity area on Friday was easily able to trigger a size 1.5 very thin slab avalanche, in a steep north facing couloir at Treeline.

Large settlements and whumphing have been reported recently, in previously untracked terrain.

Snowpack Summary

Ongoing snowfall is covering a generally weak and facetted snowpack. Storm snow accumulations should reach ~15cm by Saturday morning, with an additional 20-25cm forecast to fall through out the day

The alpine snowpack is particularly thin and variable for this time of year, with shallow areas facetted and unconsolidated from the snow surface to the ground.

There are several persistent weak layers buried, which are most prevalent at and near treeline. The Dec 16 interface is down ~20cm, and consists of surface hoar (up to 10mm) and a crust on solar aspects. The Dec 5 surface hoar layer is down ~40cm. The Nov. 17th surface hoar/suncrust layer is down ~80cm and is the suspected failure plane for recent whumphing locally, and some large avalanches in neighboring areas.

Weather Summary

A moist pacific system continues to drive weather inland from the Coast.

Up to 35cm will fall Friday night through Saturday evening, with the heaviest snowfall happening midday. Ridgetop winds will increase to strong from the SW, and alpine high temps will be -4°C.

Sunday will be a break between fronts. Scattered flurries will give up to 4cm, the alpine high will reach -2*C with a 1600m freezing level , and ridge wind will be light gusting moderate from the SW.

Monday will bring another wave of heavy snow.

Terrain and Travel Advice

  • Watch for fresh storm slabs building throughout the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Minimize exposure during periods of heavy loading from new snow and wind.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.