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Avalanche Forecast

Archived

Mar 19th, 2022–Mar 20th, 2022

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

Regions

North Rockies.

Watch for reactive conditions on specific features. Buried weak layers are still a concern, as well as wind loading at higher elevations. 

Minimize exposure to south facing slopes during strong sunshine, avalanche danger can rise rapidly.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

SATURDAY NIGHT: 4-10 cm possible overnight. Freezing levels drop to valley bottom. Moderate southwest winds.

SUNDAY: A mix of sun and cloud with moderate southwest winds and possible afternoon flurries. Freezing levels reaching 1300 m. Alpine high of -2.

MONDAY: 5 cm possible overnight. Isolated flurries possible over the day with mostly cloudy skies. Freezing levels reaching 1800m, with strong westerly winds. 

TUESDAY: Freezing levels remain high, reaching toward 3000 m. Up to 10 mm of rain is expected. Strong southwest winds. Alpine high of +8 expected. 

Avalanche Summary

On Friday, several small wind slabs were observed to have been naturally triggered out of steep north facing terrain features. 

Avalanche activity has been tapering off over the week, with a natural cycle observed last on Wednesday. Explosive control also produced size 3 storm snow avalanches. Reactivity now appears limited to wind loaded features. 

Small loose wet avalanches were seen on all aspects below the freezing line the past 5 days, and on sun affected slopes at all elevations. Even short bursts of spring sunshine can have a significant effect on the snowpack. 

Snowpack Summary

Up to 80 cm over recent storm snow sits over a weak surface hoar layer in sheltered terrain, and on a sun crust on south facing slopes. The surface hoar hasn't shown activity in avalanches observations since Wednesday, however snowpack tests still indicate it is weak and reactive. The most concern is in wind loaded features, of the Pine Pass and the Renshaw area. 

At higher elevations consistent southwest winds are creating deeper deposits on north through east facing features. Below 1500 m, moist snow or a melt-freeze crust likely exists from recent rain and warm temperatures.

The mid and lower snowpack is generally well-settled and strong in most areas, with multiple crusts throughout. 

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.