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Avalanche Forecast

Archived

Mar 8th, 2023–Mar 9th, 2023

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Below Threshold.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Below Threshold.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Below Threshold.

Regions

Yukon, Tutshi, Wheaton, White Pass East, White Pass West.

The alpine is the most likely place to encounter triggerable wind slabs and a tricky persistent slab problem that has produced large, deep and surprising avalanches recently. Seek out sheltered treeline terrain in side valleys for the best and safest riding.

Confidence

Moderate

Avalanche Summary

On Tuesday, a size 2.5 persistent slab avalanche was remotely triggered by skiers on a ridgetop in the alpine. The slab propagated widely on a thin, rocky southeast aspect and it stepped down to basal facets lower on the slope.

On Friday, our field team observed natural wind slab avalanches up to size 2 and loose snow sluffing from steep alpine terrain around the White Pass.

Snowpack Summary

Outflow winds from the north have done a real number on the surface snow scouring exposed terrain, creating waves of sastrugi in more sheltered terrain, and forming wind slabs on southerly aspects. Very sheltered terrain in side valleys to the east and west of White Pass still harbour softer snow for riding.

The middle of the snowpack is very firm and settled. There is a surface hoar layer buried 60 cm (Powder Valley, Tuthsi, Paddy Peak) to 120 cm (White Pass) deep in sheltered, mostly north facing terrain features that produced some large, human-triggered avalanches in January and February.

At the base of the snowpack large sugary crystals persist.

Weather Summary

Wednesday night

Clear. Moderate northeasterly outflow wind. Alpine low -20 ˚C.

Thursday

Increasing cloud with flurries bringing a few cm of snow. Light to moderate northeasterly wind. Alpine inversion with a high of -10 ˚C at 1800 m.

Friday

Up to 5 cm overnight then light flurries in the morning and a mix of sun and cloud in the afternoon. Moderate to strong northeasterly wind. Alpine high -16 ˚C.

Saturday

A mix of sun and cloud. Moderate to strong northeasterly wind. Alpine high -20 ˚C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.