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Avalanche Forecast

Archived

Mar 3rd, 2021–Mar 4th, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.

This is the first significant warm-up in March and we expect this to complicate current avalanche conditions. The danger may be CONDSIDERABLE in the morning but on the rise for the afternoon. Check out the new Forecaster Blog on warming and the effects on our complex snowpack 

Confidence

Moderate - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather.

Weather Forecast

It's a hot and sunny forecast with generally light to moderate south wind. Thursday through Saturday will see mostly sunny skies with patches of cloud cover. Freezing levels are forecast to rise above 2000 m driving alpine temperatures above freezing. Sunday should bring cloud cover and a cooling trend. 

Avalanche Summary

No recent avalanche reports on Wednesday.

Sun and warming is our primary concern over the next few days. Large looming cornices may weaken and fail, triggering slabs on the slopes below. Loose-wet avalanches will likely be seen from solar aspects first and then possibly all aspects. The persistent slab sitting above weak layers may stiffen and consolidate further, failing as a natural avalanche or becoming more sensitive to skier and rider triggers. 

Pockets of wind slab may be reactive on northeast-east aspects at upper elavtions. 

Snowpack Summary

Large, looming cornices exist on many ridgelines and threaten slopes below. Strong west-southwest winds have formed wind slabs on leeward slopes while freezing rain formed a widespread breakable crust 1-5 mm below 1800 m and in spotty locations at upper elevations. 

Up to 50 cm of snow sits above a variety of old interfaces that formed mid-February and 60-100 cm down is a persistent weak layer that was buried in late January. These mostly include sugary facets, hard wind pressed surfaces, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. The South Rockies Field Team was near the powder cowboy sled zone today and their snowpack tests showed easy results (CTE 7 SC down 60) on a persistent weak layer.

There are no deeper layers of concern.

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • 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.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.