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Avalanche Forecast

Archived

Mar 17th, 2021–Mar 18th, 2021

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

Regions

Cariboos.

New snow and strong wind may form isolated pockets of fresh wind slab.

The region will mostly see cloud cover on Thursday, however; if the sun pokes through it could heat slopes quickly. Pay attention to steep South facing slopes and back off them if they heat up.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A Pacific frontal system approaching the coast on Thursday will start to force some upper-level cloud cover to the Interior Mountain Ranges. Freezing levels will be between 1500-1800 m. By Friday the system will bring unsettled weather with new snow and cloudy skies.

Thursday: Mix of sun and cloud with snow up to 5 cm. Alpine temperatures near -5 and freezing levels 1800 m. Ridgetop wind light from the South.

Friday: Mostly cloudy with another 5 cm of new snow. Alpine temperatures near -5 and freezing levels 1400 m. Ridgetop wind moderate from the South.

Saturday: Cloudy with sunny periods and flurries. Alpine temperatures near -11 and freezing levels 1200 m. Ridgetop wind moderate from the southwest.

Avalanche Summary

No additional avalanche observations reported Tuesday. 

Wind slabs may be reactive on Thursday in areas that receive some fresh snow and strong wind. These will likely be isolated to the immediate lee of ridgetop features. Daytime warming combined with solar radiation may pack enough punch to trigger loose wet avalanches, especially on sunny aspects. Large looming cornices may also become weak and fragile with warming. 

Snowpack Summary

Strong ridgetop wind accompanied by 5-10 cm of new snow is expected for Thursday. This may form fresh wind slabs below alpine ridgetops. Dry snow can be found on north aspects and crusty snow surfaces exist on solar aspects. Large cornices loom over alpine ridges and become weak with afternoon warming.

A persistent weak layer made up of surface hoar at treeline elevations and a crust with facets in the alpine on solar aspects can be found down 50-150 cm in some parts of the region. Only one recent avalanche has been reported on a deeper layer and this involved a very heavy trigger (a cornice).

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.

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.

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.