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Avalanche Forecast

Archived

Mar 20th, 2021–Mar 21st, 2021

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

Regions

North Columbia.

Expect to find an increasingly reactive slab as snowfall accumulates and anywhere fresh snow is influenced by the wind. Be mindful that the best riding conditions may overlap with the deepest deposits and touchiest slabs.

Confidence

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

Weather Forecast

SATURDAY NIGHT: Flurries, up to 5 cm. Light to moderate southwest wind, alpine temperature low -8C, and freezing level dropping to valley bottom.

Weather models are showing a band of moisture moving from the Shuswap to the Purcells through the Nakusp area to the TCH corridor late Saturday evening and overnight, and may produce enhanced precipitation in localized areas of up to 25cm.

SUNDAY: Flurries and snow, 10-20 cm accumulating by the end of the day. Moderate southwest wind, alpine high -3C, and freezing level beginning near valley bottom rising to about 1400 m.

MONDAY: Flurries continuing into Monday, 5-10 cm of snow possible. Light northwest wind, alpine high -6C, and freezing level beginning near valley bottom rising to about 1300 m.

TUESDAY: Mostly cloudy. Light to moderate southwest wind, alpine high -1C, and freezing level beginning near valley bottom rising to about 1400 m.

Avalanche Summary

On Friday, several glide slab avalanches (size 2-3) were observed on south and east aspects around the TCH highway corridor. Loose wet avalanches to size 2.5 were reported around the region; a natural loose-wet cycle was reported around Rogers Pass initiating with evening rainfall.

Avalanche activity on Thursday was limited to two glide slabs to size 2.5 releasing around 1750 m on steep south facing slopes.

On Tuesday, a size 3.5 deep slab avalanche was reported from the Northern Monashees. It was triggered by cornice fall on an east-southeast aspect above 2200 m. Additionally, a natural glide slab size 2.5 was reported from a West aspect at 1500 m and numerous loose wet to size 2 in steep southerly terrain. 

On Monday, numerous natural loose wet avalanches were reported from southerly aspects above 1900 m.

Snowpack Summary

15-30 cm snow accumulated around the region through Saturday. Flurries and wind formed fresh slabs in immediate lees. New snow covers dry settled snow and surface hoar (up to 10 cm) on northerly aspects above 2000m, and crusts on solar aspects and lower 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

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Wind slabs are most reactive during their formation.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Dial back your terrain choices if you are seeing more than 25cm of new snow.

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.