Avalanche Forecast

Issued: Jan 28th, 2021 1:00AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Persistent Slabs, Wind Slabs and Storm Slabs.

Ryan Shelly, VIAC

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 forecaster@islandavalanchebulletin.com This forecast brought to you collaboratively by shadow forecaster Dave Kallai and forecaster Ryan Shelly

Summary

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

There hasn’t been any activity, but we are still concerned about our two persistent weak layers (PWL) that form our persistent slab problem. Since this layer isn’t currently reactive to skier traffic, the likelihood may be low. However, this layer is deep in the snowpack, and with an increased load such as a cornice fall, it could be triggered, creating a large avalanche. Location: Found at all elevation bands and on multiple aspects. Possibility: Unlikely to Possible from natural and human triggers. Size: If triggered, expect these avalanches to be large enough to bury a person (size 2-3).

Likelihood

Possible

Expected Size

1 - 1

Wind Slabs

The recent winds have produced Wind slabs that can be found predominantly on North aspects. This wind slab overlies either a thick crust or a surface hoar layer, making it unstable. On Tuesday, the wind is forecasted to increase and switch to an easterly direction creating a cross-load wind slab problem in alpine and tree line features. Location: All aspects at alpine and treeline. Possibility: Triggering of this avalanche problem is “possible to “likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “possible” to “unlikely” depending on the elevation band. Size: If triggered, expect these avalanches to be large enough to bury a person, size 2.

Likelihood

Possible

Expected Size

1 - 1

Storm Slabs

The recent storm created storm slabs in areas less exposed to the wind. This is present in all aspects and elevations. Location: All aspects and at all elevation bands into Tuesday. Possibility: Triggering of this avalanche problem is “possible” to “likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are possible to unlikely depending on the elevation band. Size: If triggered, expect these avalanches to be large enough to bury a person, size 2

Likelihood

Possible

Expected Size

1 - 1

Valid until: Jan 29th, 2021 1:00AM