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Avalanche Forecast

Archived

Mar 20th, 2021–Mar 21st, 2021

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

Regions

South Columbia.

More snow is forecasted around the region with enhanced precipitation in localized areas. Expect to find an increasingly reactive slab as snowfall accumulates and anywhere fresh snow is influenced by the wind.

Confidence

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

Weather Forecast

SATURDAY NIGHT: Flurries, 5-15 cm. Light to moderate northwest wind, alpine temperature low -6C, 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 late Saturday evening and overnight, and may produce enhanced precipitation in localized areas of up to 25cm. 

SUNDAY: Snow and flurries, with up to 25 cm accumulating by the evening. Highest precipitation amounts are forecasted for the Monashees and southwest of Revelstoke. Moderate southwest wind, alpine high -3C, and freezing level beginning near valley bottom rising to about 1100 m.

MONDAY: Cloudy with sunny breaks and isolated flurries, up to 10 cm of snow possible. Light northwest wind, alpine high -4C, and freezing level beginning near valley bottom rising to about 1300 m.

TUESDAY: Mostly sunny with patchy clouds. Light to moderate southwest wind, alpine high +1C, and freezing level beginning near valley bottom rising above 1500 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 up to size 2.5 were reported around the region; a natural loose-wet cycle was reported around Rogers Pass initiating with evening rainfall.

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

10-20 cm fresh snow accumulated around the region through Saturday with more forecasted through Sunday. 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

  • Dial back your terrain choices if you are seeing more than 25cm of new snow.
  • Closely monitor how the new snow is bonding to the old surface.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.