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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

South Rockies.

 

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 50 km/hr gusting to 75 km/hr from the southwest and alpine temperatures near -5. Freezing levels valley bottom.

Wednesday: A mix of sun and cloud. Ridgetop wind strong from the southwest and alpine temperatures near -4. Freezing levels 2000 m.

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

Avalanche Summary

We received no avalanche reports on Sunday. 

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

Extreme ridgetop wind from the West has formed wind slabs in exposed terrain at treeline and alpine elevations. Loose-dry surface sluffing may occur from steep terrain features. 40 to 60 cm (in some places up to a meter) of snow now sits above sugary faceted snow that formed mid-February. Snowpack testing done by the South Rockies field team on Saturday in the Mear Lake area showed a relatively easy to moderate failure on the mid-Feb layer which propagated across the whole column (ECTP 13 down 40 cm). This indicates that a 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. On Wednesday a rider-triggered avalanche size 3 was reported on this interface. 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.