Avalanche Forecast

Issued: Apr 14th, 2021 2:00AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Cornices, Loose Wet and Wind Slabs.

Ryan Shelly, VIAC

Vancouver Island.

Cornice Fall and wet loose avalanches observed in steep unsupported terrain (size 1) observed at Below Treeline elevations on Monday April 12th. Suspect similar events on terrain and aspect will take place at higher elevations with greater consequence as the freezing level rises above mountain top on Vancouver Island for the first time in many months.

Summary

Past Weather

Several snow storms and overnight cold temperatures have elongated winter on polar aspects on Vancouver Island. This melt freeze chapter will come to a close as "summer like" air temperatures will visit Vancouver Island for the next several days.

Weather Forecast

Near double digit air temperatures near mountain top as "day time high's" will inhibit snowpack cooling overnight and consistently weaken near surface snowpack layers and cornices. Wednesday: No new precipitation Winds light from the North, Freezing level rising during the daytime to 2250 meters. Temps at 1500 meters up to +8 degrees.Thursday: No new precipitation, Winds light shifting from South to North at mid-day, Freezing level rising to 2,400 meters. Temps at 1500 meters up to + 9 degrees.Wednesday: No new precipitation, Winds light shifting throughout the day from North to South, Freezing levels 2700 meters. Temps at 1500 meters 10 degrees.

Terrain Advice

Please respect the current closures at Mount Washington, no access is permitted at anytime on the ski areas slopes or terrain.During periods of intense warming and sunshine avoid solar aspect terrain.Avoid travelling both above and below cornices.

Snowpack Summary

New snow between 5 and 20 cm overlies a previously well developed melt/freeze crust. Warm (above zero) daytime temperatures and moderate settlement of this new snow has promoted bonding of this new layer of snow. Wind affected areas and continued cornice growth is evident and cornice fall is evident. The mid and lower snowpack are well settled and dense.Forecast temperature values are expected to rise rapidly and overnight cooling and snowpack recovery (refreeze) will dissapear as nighttime "low's" will not drop below zero degrees on Vancouver Island's mountain ranges. With these factors, the snowpack will begin to rapidly settle and is likely to become increasingly unstable as these elevated air temperatures have not been experienced on Vancouver Island for many months at the upper Treeline and Alpine elevation bands. Expect cornice collapse, glide slab failures, waterfall ice failures and perhaps other anomalous geo hazard events to occur as the mountains are going to see a rapid change from winter conditions to near summer like conditions in a 72 hour period.

Snowpack Details

Surface: 5cm snow to 20cm snow (depending on elevation band) on Northerly terrain exists however will begin to melt with incoming air temps
Upper: Large melt freeze crust (35cm thick) and above 1400M elevation (5cm thick)
Mid: warm moisture laden snowpack at Below Treeline elevation and generally well settled and dense above 1400M
Lower: Well settled and dense.

Confidence

High - Moderate - Avalanche danger ratings reflect the highest danger level expected over the course of the day. Weather forecast models are very well aligned and provide support to the forecasted avalanche problems.

Problems

Cornices

Cornices continued to grow with the last snow fall and strong south west wind, Expect this problem become increasingly sensitive as daily temperatures and freezing level rise. The probability of natural cornice failures occurring in the heat of the day on Wednesday are near certain. Location: Predominantly north aspects at ridge top in the Alpine and Tree line. Possibility: Triggering of this avalanche problem is likely to very likely from light loads such as skiers. Natural avalanches are very likely. Size: If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3

Likelihood

Possible

Expected Size

1 - 1

Loose Wet

The loose wet avalanche problem will become widespread as overnight temperatures are forecast to not provide enough cooling to refreeze the upper snowpack, expect south facing terrain to become rapidly unconsolidated as temps rise and the sun begins to directly radiate surfaces. Location: South Aspects at all elevations Possibility: Triggering of this avalanche problem is very likely from light loads such as skiers. Natural avalanches are very likely. Size: Expect widespread size 1 to 2 avalanches

Likelihood

Possible

Expected Size

1 - 1

Wind Slabs

Wind slabs in isolated lee terrain at higher elevation will continue to gain strength and settle but may still continue to present in terrain well protected from the sun. Location: North East thru to North West aspects and found in the Alpine Possibility: Triggering of this avalanche problem is possible from light loads such as skiers. Natural avalanches are unlikely. Size: If triggered expect these avalanches to be large size 2 and in isolated terrain very large size 3.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Apr 15th, 2021 2:00AM