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Avalanche Forecast

Archived

Mar 21st, 2023–Mar 22nd, 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

.

Recent avalanches have shown an ability to propagate far and deep in the snow pack.

Large slopes are still a concern and are most likely to be triggered in thin rocky areas.

Confidence

Moderate

Avalanche Summary

No new avalanches were reported in the region on Monday. Backcountry users may see evidence of a large avalanche cycle from the weekend as they travel through the terrain. These avalanches may have occurred during last week's storm or due to solar input and elevated freezing levels through the weekend.

On Sunday, a suspected skier triggered avalanche was reported. This was a size 1 storm slab avalanche that likely occurred on Saturday.

If you head out in the backcountry, let us know what you are seeing by submitting a report to the Mountain Information Network.

Snowpack Summary

Last week's storm that delivered 50 cm of new snow to both passes has been heavily wind affected in the alpine with less wind affect at lower elevations where it is capped by a thin crust below 1300 m. In sheltered northerly aspects there is up to 20 cm of soft snow still hiding from the wind.

A buried weak layer of surface hoar can be found about 80 cm deep in Powder Valley, Tutshi, and Paddy Peak areas, 150 to 200 cm around White Pass and 80-200 cm deep in Haines Pass. This layer is most prominent on northerly slopes sheltered from the wind. On other aspects, this layer is a hard melt-freeze crust with weak facets around it. This layer has been most problematic in alpine terrain.

The remainder of the middle of the snowpack is consolidated and strong. Weak faceted grains are found near the base of the snowpack, particularly in thin snowpack areas.

Weather Summary

Tuesday Night

Mainly cloudy with scattered flurries, 5 cm accumulation. Strong southwest ridge top winds. Alpine temperature low -12°C. Freezing levels valley bottom.

Wednesday

Mainly cloudy with isolated flurries, 4-6 cm accumulations. Strong south ridge top winds. Alpine temperature high -9°C. Freezing levels 500 m.

Thursday

Partly cloudy with isolated flurries, 4 cm accumulations. Moderate southeast ridge winds. Alpine temperature high -8°C. Freezing levels 700 m.

Friday

Mainly cloudy with isolated flurries, trace cm accumulations. Light south ridge winds. Alpine temperature high -9°C. Freezing levels 500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Be carefull around freshly wind loaded features.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.

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.