Avalanche Forecast
Issued: Jan 25th, 2021 1:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Wind Slabs and Storm Slabs.
Ryan Shelly,
VIAC
Multiple reports of size 1 and size 2 skier triggered avalanches throughout the forecast area. These avalanches have been reported as 'slab' avalanches, they will remain sensitive to skier/snowmobile triggering as the reports include shooting cracks.
Summary
Past Weather
The past week saw cool clear calm temperatures allowing for the growth of two separate (PWL's) within the upper snowpack. A storm cycle on Sunday brought close to a foot of new snow to various parts of the forecast region and along with it a variable deposition of the new snow as winds in certain regions redistributed new snow to downwind areas.
Weather Forecast
On Monday, a weak low pressure system with periods of snow over the island. The highest accumulation of precipitation will likely occur from the central portion of the island and to the South. This low is expected to dissipate by Monday night. As the storm subsides, cold air from the interior will move to the coast which will be accompanied by strong outflow winds developing on Tuesday and into Wednesday. Monday: 10cm to 30cm Snow, High - 3 Low -5, Light Winds from the NW, Freezing level 550MTuesday: 5cm to 10 cm Snow, High -1 Low -4, Moderate to Strong winds from the East, Freezing level 500M Wednesday: 2cm to 5cm Snow, High -3 Low -8, Freezing level 400M
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 steel unsupported terrain. On Tuesday, with the continuation of the storm and potential 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.
Snowpack Summary
10-30cm of wind affected new snow overlies an array of supportive melt freeze and rain crusts within the upper 50cm to 70cm of the upper snowpack. The crust at the Below Treeline elevation band is extremely supportive and providing difficult snowmobile and ski conditions in wind exposed areas where the new snow is no longer present.
Snowpack Details
- Surface: 10cm to 30cm of new snow overlies surface hoar (PWL) in specific areas (wind sheltered terrain)
- Upper: 40cm 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
Confidence
High - Weather models in agreement, a great deal of professional and recreational observations. This weeks report brought to you in collaboration with shadow forecaster Dave Kallai and Forecaster Ryan Shelly
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
Expected Size
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" from light loads such as skiers,
snowshoers and snowmobilers. Natural avalanches are "possible" to "likely" depending on the
elevation band.
Size: If triggered, expect these avalanches to be large enough to bury a person, size 2.
Likelihood
Expected Size
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
Expected Size
Valid until: Jan 26th, 2021 1:00AM
