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Avalanche Forecast

Archived

Mar 18th, 2022–Mar 19th, 2022

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

Regions

North Rockies.

Buried weak layers are keeping danger ratings elevated. Watch for signs of instability like whumpfing, natural avalanches and cracking.

Watch for fresh wind loading at higher elevations from southwest winds. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

FRIDAY NIGHT: Cloudy, isolated flurries bring up to 5 cm overnight. Freezing levels drop to 500 m. Moderate southwesterly winds. 

SATURDAY: Partly cloudy, 3-10 cm over the day. Freezing levels reach 1500 m. Moderate southerly winds turn west in the afternoon. Alpine high of -1.

SUNDAY: Around 5 cm possible overnight. A mix of sun and cloud with moderate southwest winds. Freezing levels reaching 1500 m. Alpine high of -2.

MONDAY: Isolated flurries possible with mostly cloudy skies. Freezing levels reaching 1800m, with strong westerly winds. 

Avalanche Summary

On Thursday, several wind slabs to size 1.5 were observed in north east facing alpine features, lee to the southwest winds. Check out this MIN report for a good description of current snowpack conditions, they noted shooting cracks and signs of instability on their trip.

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

On Wednesday, explosive control south of Renshaw produced avalanches up to size 3 within the recent storm snow. Natural activity was observed in specific wind loaded features around ridgelines to size 1.5.

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 has shown recent reactivity, with the most concern in Pine Pass and the Renshaw area. 

At higher elevations consistent southwest winds are creating deeper deposits on north through east facing features. Below 1300 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.