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Avalanche Forecast

Archived

Feb 28th, 2021–Mar 1st, 2021

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

Regions

South Rockies.

A reactive persistent slab exists and can be easily triggered by a skier or rider. A conservative mindset and patience are required.

Fresh wind slabs may be reactive on east to northeast slopes on Monday. 

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

The dominating features associated with this next frontal system will be wind and slight warming. Ridgetop wind is forecast 50-90 km/hr from the southwest through the forecast period. Light snowfall amounts expected.

Monday: Cloudy with a trace of snow. Ridgetop wind 55-70 km/hr from the southwest. Alpine temperatures -2 and freezing levels 1300-1700 m.

Tuesday: Mix of sun and cloud with flurries. Ridgetop wind 50-90 km/hr from the southwest. Alpine temperatures -3 and freezing levels 1000-1500 m. 

Wednesday: Trace of snow and ridgetop wind 35-60 km/hr from the southwest. Freezing levels 1600 m.

Avalanche Summary

Almost daily we're receiving 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 Monday and loose-dry avalanches may spill from steeper terrain features, especially when the sun is out. 

Snowpack Summary

Extreme ridgetop wind from the West has formed reactive wind slabs in exposed terrain at treeline and alpine elevations. Loose-dry surface sluffing may occur from steep terrain features. 30 to 60 cm of snow now sits above sugary faceted snow that formed mid-February. Snowpack testing done on this layer Saturday in the Mear Lake area showed a relatively easy to moderate failure which propagated across the whole column (ECTP 13 down 40 cm). This indicates that the persistent slab can be triggered by the weight of a person and produce a consequential avalanche. This test was on a south-facing slope at treeline. 

Deeper in the snowpack (50 to 90 cm deep) is yet another weak layer that was buried at the end of January. This layer consists of surface hoar, faceted grains, and/or a hard melt-freeze crust and continues to be reactive to skier and rider triggers. Check out this MIN report from Ruault Lake area in the western flank of the region. 

Weak faceted grains and a decomposing melt-freeze crust can be found near the base of the snowpack. 

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.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Choose simple, low-angle, well supported terrain without convexities.
  • 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.