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Avalanche Forecast

Archived

Mar 1st, 2021–Mar 2nd, 2021

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

Lizard-Flathead.

There is still the potential to trigger persistent weak layers. These are producing large and consequential avalanches. A conservative mindset and patience are required.

Fresh wind slabs may be reactive to human triggers on northeast and east slopes.

Confidence

Low - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Tuesday: Cloudy with a trace of new snow. Ridgetop wind 20 km/hr gusting to 70 km/hr from the southwest and alpine temperatures near -4. Freezing levels 900 m.

Wednesday: A mix of sun and cloud. Ridgetop wind light from the southwest and alpine temperatures near -2. Freezing levels 2000 m.

Thursday: A mix of sun and cloud and freezing levels rising to 2000-2500 m.

Avalanche Summary

No new avalanches reported on Monday. 

On Sunday skier triggered wind slabs up to size 1 were reported. These were 10-20 cm deep and found along ridgelines and open slopes. 

Our primary avalanche problem is persistent slabs. The persistent slab is down 40-100 cm and mostly found around treelne elevations. It is likely to trigger by the weight of a skier or sledder, initiating large and consequential avalanches. Almost daily we've received reports of skier and rider-triggered persistent slab avalanches from the SoRo and Lizard forecasting regions. These avalanches have been size 2 or larger and have caught people by surprise. This problem is not healing quickly and the conditions are not easily managed. A conservative mindset and patience are crucial right now.  

New wind slabs may exist on East to Northeast aspects on Tuesday and loose-dry avalanches may spill from steeper terrain features, especially when the sun is out. 

Snowpack Summary

Strong west-southwest winds have formed reactive wind slabs on leeward slopes and solar aspects have a thin 1-3 mm sun crust. Up to 50 cm of snow sits above a variety of old interfaces that formed mid-February. These mostly include sugary facets, hard wind pressed surfaces, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. Another persistent weak layer is found down 60 to 100 cm deep and was buried late-January. This layer consists of similar weak snow crystals mentioned above and continues to be reactive by the weight of a person.

There are presently no deeper concerns.

Terrain and Travel

  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • In times of uncertainty conservative terrain choices are our best defense.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.

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.