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Avalanche Forecast

Archived

Jan 28th, 2021–Jan 29th, 2021

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

Regions

Vancouver Island.

On Tuesday Jan 26 and Wednesday Jan 27, reports of size 1 and 2 skier triggered avalanche within the forecast area. Avalanches appear to be soft slab in nature and are not showing hard slab properties that could promote propagation. For this reason we have downscaled the avalanche hazard now that the storm has passed. Human triggered avalanches at the Alpine elevation bands are considered likely” Thursday. Thank you Griffin Fisk, Theron Finley, Sportnewk, Gilbert and Andrew S for posting to the MIN and Joe, Cliff, Abby Rutherford, Kalen and Tim Plante for sending OBS in to [email protected] This forecast brought to you collaboratively by shadow forecaster Dave Kallai and forecaster Ryan Shelly

Past Weather

New snow, cold temperatures and some wind affect have made for outstanding snowmobiling and skiing/snowshoeing since the storms arrival several days ago. As a result of all the new snow, it appears that avalanche activity is occuring within the upper 20cm to 50cm of the upper snowpack. Expect this problem to increase as additional new snow arrives into the weekend for specific areas within the forecast region.

Weather Forecast

More snow and consistent cooler temperatures are incoming for the next several days. Expect the weather to become a bit more aggressive on the weekend as strong winds and strong precipitation rates arrive Saturday January 30th. Light precipitation for the East and North end of the forecast region while the West and South end of our bulletin area stand to receive strong amounts of snowfall. Thursday: 1cm Snow, Moderate winds from the East shift to Light East winds at mid-day, Freezing level 750MFriday: 2cm to 10 cm Snow, Light SE winds shifting to Moderate SE winds at mid-day, Freezing level 800MSaturday: 10cm to 40cm Snow, Strong SE winds, Freezing level 850M

Terrain Advice

The recent storm snow has formed slabs in specific downwind areas that are reactive to human triggering. Be aware of the potential for loose dry snow avalanches in steep unsupported terrain. On Wednesday, with the continuation of the storm and wind, cross loaded and down wind areas will remain a concern to prioritize if venturing into avalanche terrain. Be conservative when travelling nearby to cornices as they are generally unstable (very much so at this time during a storm/wind cycle). Maintain a close eye on the transition areas between wind scoured and snow loaded areas as these zones can be good areas to initiate avalanches at this time.Simple Avalanches Terrain ( terrain generally under 30 degrees) would be the place to recreate at this time given the dynamic weather we are experiencing at this time.

Snowpack Summary

20-50cm of wind affected new snow overlies an array of supportive melt freeze and rain crusts within the upper 60cm to 80cm of the upper snowpack. The crust at the Below Treeline elevation band is now buried and is sensitive to triggering.

Snowpack Details

  • Surface: 20cm to 40cm of loose dry powder snow overlies surface hoar (PWL) in specific areas (wind sheltered terrain)
  • Upper: 20 to 50cm below the surface exists a melt freeze crust with facets (PWL) resting above this crust
  • Mid: Generally well settled with several melt freeze crust layers
  • Lower: Well settled and well bridged and includes a 10cm thick layer of large facets (Dormant PWL)

Confidence

High - Variability in terms of precipitation rates (Saturday Jan 30) across Vancouver Island, Good variety of field data available.

Problems

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.

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.

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.