Avalanche Forecast
Issued: Mar 17th, 2021 2:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Cornices, Wind Slabs and Storm Slabs.
Ryan Shelly,
VIAC
Some loose wet avalanches (size 1.5) observed on open and steep terrain by forecaster on duty. Some larger slab avalanches (size 2+) also observed by forecaster on duty, slabs appeared to have occurred as a result of day time warming on Southerly facing aspects on steep Alpine features (observed in Strathcona Park).
Summary
Past Weather
Predominantly clear conditions, light winds and daytime warming and sun baking all southerly aspects.
Weather Forecast
We have entered a spring diurnal cycle but we may be in luck that winter hasn't quite left the building! Wednesday: No new precipitation. Winds Moderate from the SE , Freezing level rising during the daytime to 1,200 meters. Thursday: 10cm Snow to 20cm snow throughout forecast area (excluding Arrowsmith and South Island who will experience less than 5-10cm Snow), Winds Strong from the SE (with Extreme SE gusts), Freezing level rising to 1,380M for South Island, Freezing Level rising to 1,100M for Central and North Island. Friday: 20cm Snow to 40 cm Snow , Winds Strong from the SE (with Extreme SE gusts), Freezing level rising to 1400M South island, Freezing Level will reach 900M elevation for North and Central Vancouver Island.
Terrain Advice
The snow is holding cold on Northerly facing terrain near 1400M and above. At the lower elevation bands, the air temperature has subjected the snowpack to a spring Melt-freeze cycle that is posing challenging ski/sledding conditions. Due North facing slopes are holding the coldest snow, particularly in wind protected areas where winds have not impacted snow quality. By Thursday however conditions will change as new precipitation and winds arrive to the island. Practice patience and allow time for new storm instabilities to stabilize prior to committing to any steep terrain.Plan routes and choose terrain that is low angle and supportive as you begin to venture into unmodified and uncontrolled snowpack and terrain.Identify and avoid travel either above or below cornice features.Adjust travel plans to ensure avoidance of solar aspects during warming and when the sun is out.
Snowpack Summary
Storm event from the weekend has settled as soft snow on Northerly aspects at Treeline at Above (and some Due North facing BTL slopes still hold cold dry snow too!) Southerly facing aspects at all elevation bands have been subjected to major day time heating and as a result are offering challenging "riding quality" until afternoon daytime high's (Air temp above zero) begin to soften the snowpack. Generally speaking, the snowpack is well bonded (bridged) despite a series of upper, mid-pack and basal layers.
Snowpack Details
- Surface: Dry soft snow on North facing (TL and Alp) slopes and a melt freeze crust on all Southerly aspects and elevation bands
- Upper: Last weekends storm snow interface with old snowpack is bonding but showing reactivity in unsupported terrain
- Mid: Well settled due to melt freeze cycle snowpack has undergone. Does include a melt freeze crust/small facet interface down 70cm
- Lower: Well settled and dense. Does include a basal melt freeze crust/ facet interface down 120cm
Confidence
Moderate - Weather models in agreement. Moderate data collection. Some uncertainty in terms of precipitation volume and type (Rain/Snow) .
Problems
Cornices
Very large cornices exist and continued snowfall, wind and high humidity continue to promote cornice growth. Cornice failures have the potential to over load the snowpack and trigger both new snow instabilities as well deeper instabilities. Expect the new growth to be fragile and when temperatures and freezing levels rise become suspected triggers in bigger avalanche events.
Location: North thru to West aspects at ridges top in the Alpine and Tree line.
Possibility: Triggering of this avalanche problem is likely to very likely from light loads such as skiers/snowmobilers. Natural avalanches are possible to likely.
Size: If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3
Likelihood
Expected Size
Wind Slabs
This new avalanche problem will be sensitive to triggering in areas where precipitation arrives in excess of 20cm coupled with strong winds. The wind slab issue will become increasingly unstable into Friday as an additional 30cms of snow is expected to arrive with strong winds. Found on predominantly Northerly and downwind aspects. This avalanche problem will arise beginning on Thursday, forming as a result of new snow and strong winds and will overlie a variety of snow surfaces (including surface hoar in isolated areas and a firm melt crust.
Location: North aspects and found in both the Alpine and Tree line.
Possibility: Triggering of this avalanche problem is likely to very likely from light loads such as skiers/snowmobilers. Natural avalanches are possible to likely.
Size: If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3 .
Likelihood
Expected Size
Storm Slabs
This new avalanche problem will develop on Thursday in areas that receive snow in excess of 20cm- sensitivity to triggering will increase over the course of the storm event. On isolated Alpine terrain expect this new snow to overly buried surface hoar. On solar aspects, expect the storm snow to overlie a melt freeze crust.
Location: All aspects, Alpine and Tree line. Below tree line hazard is from above.
Possibility: Triggering of this avalanche problem is likely to very likely from light loads such as skiers/snowmobilers. Natural avalanches are possible to likely.
Size: If triggered expect these avalanches to be large size 2 (by Friday), on isolated terrain features very large, size 3 (by Friday).
Likelihood
Expected Size
Valid until: Mar 18th, 2021 2:00AM
