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Avalanche Forecast

Archived

Feb 4th, 2021–Feb 5th, 2021

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

Regions

South Coast Inland.

Overnight snowfall and wind will keep storm slabs fresh Friday. In areas that receive less than 10 cm of new snow, avalanche danger may be a step lower.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Thursday night: Snow, 5-10 cm for most areas with a possibility of locally enhanced snowfall amounts as high as 20 cm near Hope and 30 cm along the southern border of the region. Moderate to strong westerly ridgetop wind, alpine temperature near -7.

Friday: Mainly cloudy with a few flurries, moderate northwest ridgetop wind, alpine high -4, freezing level rising to 1200 m.

Saturday: Mostly cloudy with flurries, moderate westerly ridgetop wind, alpine high -8, freezing level 800 m in the north, 1300 m in the south.

Sunday: Mix of sun and cloud, light variable wind, alpine high -10, freezing level valley bottom.

Avalanche Summary

In the clear weather on Wednesday, evidence of a widespread natural storm slab avalanche cycle up to size 2 was observed. It is suspected to have occurred during the storm on Monday night. Since this event, there have been reports of natural, explosive and human triggered avalanches size 1-1.5. Many of these failed on the recently buried persistent weak layer.

Snowpack Summary

Overnight snowfall with moderate to strong northwest winds will likely form reactive slabs in the alpine and open treeline areas. The south of the region may see enhanced snowfall amounts as high as 30 cm.

30-80 cm of recent snow sits on a persistent weak layer that consists of facets at upper elevations, surface hoar in sheltered areas, a melt-freeze crust below 1600 m, and a sun crust on south-facing slopes. 

In the south, the underlying snowpack is well consolidated. In the north, a melt-freeze crust from early December may be found 100 to 200 cm deep. Recent reports suggest that this layer is gaining strength and it has been unreactive in recent weeks.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid freshly wind loaded terrain features.
  • Be aware of highly variable recent wind loading patterns.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.

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.