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Avalanche Forecast

Archived

Mar 19th, 2022–Mar 20th, 2022

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

Regions

North Columbia.

Conservative terrain choices are advised, buried weak layers still remain reactive on specific features. 

Expect avalanche danger to increase as the sun hits the snowpack. Triggering avalanches will become more likely on sun affected slopes. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

SATURDAY NIGHT: 5-10 cm possible overnight, higher accumulations around 15 cm likely concentrated near Eagle Pass. Moderate southwesterly winds. Freezing levels drop to valley bottom.

SUNDAY: A mix of sun and cloud with light westerly winds. Freezing levels around 1300 m, alpine high of -3. 

MONDAY: Flurries possible with light southwest winds. Mostly cloudy. Freezing levels rise to 1500 m. Alpine high of -1.

TUESDAY: Freezing levels only push higher, reaching near 2500 m. A mix of sun and cloud. Moderate southwest winds. Alpine high +4. 

Avalanche Summary

Overall reports indicate a gradual tapering of reactivity of the buried weak layers, however reactivity remains in specific features where these weak layers are more prominent. 

On Friday, wind loaded features produced up to size 1.5 natural slab avalanches in many areas.

There is continued evidence of recent natural activity to size 3 on the early march weak layers (primarily south facing slopes) that has occurred within the last 3 days. Natural and rider triggered slab avalanches to size 2 on south and east facing slopes on the crust. Explosive control work Friday produced a size 3 slab, failing on the buried surface hoar layer on a north facing treeline slope. 

Loose wet avalanches have been reported at elevations below the freezing line over the past 5 days. 

Snowpack Summary

Up to 60 cm of recent settling storm snow sits over a layer of weak surface hoar in sheltered and shaded terrain, and over a crust on south facing slopes. Test results show that the new snow is bonding poorly to old surfaces in many areas, producing large avalanches within the last 3 days and reactive results to tests. 

At higher elevations consistent southwest winds are creating deeper deposits on north through east facing features. Below 1500 m, moist snow or a melt-freeze crust likely exists from recent rain and warm temperatures.

The late February persistent weak layer combination of crust, facets and surface hoar is down 70-90 cm. Two persistent weak layers from mid-February and late January are buried 100-170cm deep. Avalanches on these layers are unlikely to be triggered.

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.