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Avalanche Forecast

Archived

Mar 19th, 2021–Mar 20th, 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 possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Potentially touchy wind slabs may form throughout the weekend on upper elevation north, northeast & east facing slopes. These fresh slabs may rest on a thin layer of surface hoar. Convective flurries could produce locally heavy snowfall, watch for rapidly changing conditions. 

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Looks like it’s back to winter for the next few days.

FRIDAY NIGHT: Freezing level lowering to about 750 m, moderate southwest wind with potential for strong gusts, 1 to 5 cm of snow possible with convection possibly delivering as much as 10 cm to favoured locations. 

SATURDAY: Overcast, freezing level rising to about 1500 m, moderate southwest wind, 2 to 8 cm of snow expected in most locations. Convective flurries could produce 15+ cm in favoured locations.

SUNDAY: Overcast, freezing level beginning near valley bottom rising to about 1500 m, light to moderate southwest wind, 3 to 6 cm of snow possible during the day with potential for 5 to 10 cm Sunday night.

MONDAY: Broken cloud cover at dawn with skies steadily clearing throughout the day, freezing level beginning near valley bottom rising to about 1500 m, light northwest wind, 1 to 3 cm of snow possible.

Avalanche Summary

On Thursday several loose wet avalanches to size two were reported on solar alpine features. Pin wheeling was also noted on north aspects below 2000 m in the afternoon.

On Wednesday a few loose-wet avalanches were seen on steep solar aspects below treeline. 

On Tuesday, a natural 1.5 loose wet avalanche was reported from steep rocky terrain and small loose-dry sluffs were easily triggered by skier traffic on northerly aspects. 

Snowpack Summary

Isolated wind slabs may form just below ridgelines with new snow and strong wind this weekend. New snow comes to rest on a variety of old surfaces including surface hoar up to 10 mm in size that exists at treeline and above. Sunny skies and warm temperatures have formed sun crusts on solar aspects at all elevations. A crust exists up to about 2000 m on polar aspects too. Dry snow still exists on north aspects at upper elevations. Large cornices loom over alpine ridgetops.

Persistent weak layers of surface hoar, crusts, and/or facets 80-120 cm down have recently been unreactive and no recent avalanches have been reported on these layers. 

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.
  • Cornices become weak with daytime heating or solar exposure.

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.

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.