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Avalanche Forecast

Archived

Feb 28th, 2021–Mar 1st, 2021

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

Regions

Northwest Inland.

Fresh and reactive wind and storm slabs exist on Monday. These slabs could step down to a deeper weak layer resulting in larger avalanches. Its a good time to be extra conservative, stick to simple terrain and avoid overhead wind-loaded slopes. 

Confidence

Low - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

A short break in systems Monday will see the precipitation ease. A zonal flow Tuesday will bring snow and strong west-southwest wind to the region through the forecast period.

Monday: A mix of sun and cloud. Snow amounts 5 cm. Ridgetop wind 25-65 km/hr from the southwest. Alpine temperatures near -9 and freezing levels 600 m. 

Tuesday: A mix of sun and cloud. Ridgetop wind 30-55 km/hr from the southwest. Alpine temperatures near -7 and freezing levels 900 m.

Wednesday: Snow 5-10 cm. Ridgetop wind moderate from the southwest. Alpine temperatures -3 and freezing levels 800 m.

Avalanche Summary

On Saturday, we received some fantastic MIN reports showing significant wind effect and wind loading at upper elevations. Natural avalanches were reported as well as a skier-triggered slab size 1.5. No new avalanche reports on Saturday. Thank you for the MIN reports!!

On Friday, fresh natural reactive wind slabs up to size 2 were reported from the alpine on E-NE aspects. 

On Thursday, numerous audible avalanches were reported in the southwestern part of the region, and an ongoing avalanche cycle was noted. 

Reactive wind and storm slabs are the primary concern for Monday. Natural avalanche activity may taper but skier and rider triggering is likely. 

Snowpack Summary

Up to 20 cm of recent snow fell by Sunday afternoon. Fresh winds slabs may be reactive on leeward slopes, while touchy storm slabs may be found in isolated wind-sheltered locations. The new snow adds to the 20-30 cm of snow that fell Thursday. This arrived with strong to extreme southwest to northwest wind and brings 50 to 80 cm of snow on a variety of old snow surfaces consisting of hard wind-affected snow in exposed terrain and weak, faceted snow or surface hoar crystals in sheltered terrain. It may take some time for the snow to bond to these old surfaces.

Basal faceted snow remains part of the snowpack structure in much of the region. Once we see a substantial warm-up, we'll be `thinking about the potential for the reactivation of basal layers.

Terrain and Travel

  • Avoid all avalanche terrain during periods of strong wind.
  • Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.