Thursday December 17, 2020

Saturday December 19, 2020
Friday December 18, 2020
Thursday December 17, 2020
Confidence: Moderate - Weather models in agreement, insufficient field data available, moderate Weather station data.

Main Concerns

Wet Slab, Wind Slab, Storm Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Careful route finding and snow-pack evaluation are paramount during periods of sustained moderate to strong snowfall this week as well as a fluctuating air temperature (Critical Warming) and strong winds.

Avoid traveling both above and below cornice features.

Careful and cautious route finding when entering into or over convex rolls or steep features.

Mt Washington Alpine Resort: A friendly reminder to please not use the resort to ski tour as machinery (including cat winches) and the possibility of explosives use will be taking place.

Avalanche Summary

No new avalanches reported

Avalanche Problems

Wet Slab

Over the next several days (particularly Friday and Saturday) Rain up to 1900M of elevation could exacerbate new storm snow instabilities with additional rain loading of fresh snow. In addition to Rain and snow events, the increased daytime warming coupled with rain on surface snow may exacerbate new storm snow layers leading to avalanches. This particular avalanche problem when triggered could result in a large avalanche up to size 2. Expect this avalanche problem to become more prevalent once the incoming rain arrives in addition to rising air temperature (particularly Friday and Saturday).

Location: On all aspects and found at Below Treeline and possibly up to the Treeline elevation band on Friday and Saturday depending on actual volume of rainfall received.

Possibility: Triggering of this avalanche problem is possible from light loads such as skiers. Natural avalanches are possible.

Size: If triggered expect these avalanches to be small, and on isolated terrain features large, size 2.

Wind Slab

Strong precipitation in the form of storm snow coupled with strong-extreme winds on Thursday to Saturday could promote wind slab instabilities (particularly in leeward or down wind areas) on Vancouver Island. Expect all Alpine/Treeline environments in leeward/down wind terrain to be likely areas to trigger a wind slab avalanche over the next several days. As of Wednesday evening- windslabs are reported to be 30-60cm in depth in the Mt Washington area, expect these values to increase as additional snowload coupled with high winds arrive again over the next several days.

Location: Leeward and down wind aspects at Alpine and Treeline elevation bands.

Possibility: Triggering of this avalanche problem is likely (depending on Elevation) from light loads such as skiers or sledders. Natural avalanches are possible to unlikely (depending on Elevation).

Size: If triggered expect these avalanches to be up to size 2 OR avalanches could appear on isolated terrain features (very large, size 3).

Storm Slab

New snow from incoming storm system will rapidly fall on a variety of surfaces. Expect this new avalanche problem to be initially very touchy to light triggers such as skiers or sledders as strong amounts of precipitation and strong winds arrive.

Location: All aspects and at all elevations. New Storm snow may fall as rain at the Below Treeline Elevation Band.

Possibility: Triggering of this avalanche problem is likely to unlikely (depending on Elevation) from light loads such as skiers. Natural avalanches are possible to unlikely (depending on elevation).

Size: If triggered expect these avalanches to be small (Size 1) -and large (up to size 2) OR avalanches could appear on isolated terrain features (very large, size 3).

Snowpack Summary

Several melt freeze crust have developed on all aspects at the Treeline and Alpine elevation bands on Vancouver Island. The upper snowpack melt freeze layer is not yet completely frozen (in certain areas) and reports show that this layer is still isothermal (0 degrees) and slushy (in certain areas). In zones where freezing temperatures have remained consistent, the upper snowpack melt freeze crust is frozen completely, a facet layer is developing and is showing results on testing at this upper snowpack melt freeze crust interface. However no reports of skier/snowmobile triggered avalanches at this time.

Snowpack Details

SurfaceDepending on Aspect and elevation, anywhere from 20cm-40cm of storm snow
UpperMelt freeze crust that varies in terms of extent of frozen characteristics (some areas report the crust as "slushy")
MidWell settled due to melt freeze cycle snowpack has undergone
LowerWell settled due to melt freeze cycle snowpack has undergone

Past Weather

It has been a productive week in terms of Vancouver Island’s mountains gaining additional snowpack. Snowfall has brought a good deal of moisture content along with it and as a result the storm snow is bonding well to the pre-existing snowpack.

Weather Forecast

Large amounts of snow and rain are forecasted as well as strong winds incoming over the next few days. Alpine and Treeline elevation bands will prevail in terms of gaining the most amount of new snow without rainfall. Strong winds for the next couple days and on Saturday Extreme winds will further exacerbate wind slabs.

Thursday: 10 -15cm Snow and 2-5mm Rain, Winds moderate from the West, Freezing levels to 950m, Temps @1500m -1.5.

Friday: 15-30cm Snow and (10-25mm Rain for east side of Island (Beaufort Range)), Winds Strong from the South, Freezing levels to 1,850m, Temps @1500m +1. (Except +4 in Beaufort Range)

Saturday: 20-30 cm Snow and (10-20mm Rain for east side of island (Beaufort Range)), Winds Extreme from the SSW, Freezing levels 1850m, Temps @1500m +1.5. (Except +6 in Beaufort Range)

Posted on Thursday December 17, 2020 by Ryan Shelly

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