Monday January 27, 2020
Cornice Fall, Deep Persistent Slab, Wind Slab, Storm Slab
Travel & Terrain Advice
Natural Avalanches possible. Human triggered avalanches likely in Alpine on unsupported terrain. There is a good amount of precipitation expected over the next several days throughout Vancouver Island. Be aware as you move through the terrain for shooting cracks and signs of instability (including new avalanches) especially at Treeline and Alpine elevation bands. Convex unsupported terrain features in leeward (down wind) terrain would be an area to be highly cautious of when navigating through the backcountry. Allow for an additional 36-48 HRS before stepping onto leeward terrain (downwind) areas particularly if the forecasted precipitation of 30+cm of new snow AND/OR signs of snow transport by strong winds exists in your area.
If these visible (snow cracking underfoot/adjacent your sled) and/or audible (whumpfing) clues exist in your area, it will be important to find lower angle terrain (generally under 30 degrees) and or ski/sled in more densely vegetated (treed) areas away from these obvious clues of snowpack instability. Check the website ATES PLANNING section for Simple Terrain options on our website.
Wet loose avalanches on steep unsupported terrain have been reported (size 1.5). Ski cutting produced size 1 avalanches on Storm Slab and wind slabs on unsupported terrain. (Size 1).
Touchy cornice features have been building and will be predominantly found on North aspects. Found in both alpine and Treeline terrain, triggering of this avalanche problem is likely from light loads such as skiers or sledders. Be leery of recreating above or below cornice features at this time.
Deep Persistent Slab
Snowpack assessments revealed a deep persistent slab problem. The likelihood of triggering this layer is unlikely given that it is 120cm down at the Below Treeline elevation band. This layer is likely deeper at Treeline and Alpine environments and no longer a potential hazard to recreational skiers or sledders. Nonetheless, it is wise to continue practicing appropriate group management techniques and only expose 1 person to the avalanche slope at a time. The reactivity of this layer is such that it would require a large trigger to initiate, such as multiple sleds on the slope at the same time or multiple skiers on the slope at the same time and or / major cornice fall hitting a slope.
Major precipitation in the form of storm snow and strong winds from the South could promote wind slab instabilities (particularly in leeward or down wind areas on Vancouver Island on Monday, Tuesday and Wednesday. Expect all Alpine and Treeline environments in leeward/down wind terrain to be likely areas to trigger a wind slab avalanche over the next several days.
Strong rates of precipitation in the form of storm snow on Vancouver Island on Monday, Tuesday and Wednesday will cause instabilities in the snowpack. Approach Alpine elevation band with caution as (human triggered avalanches likely) and the Treeline environment as (human triggered avalanches possible). A dense and well settled snowpack exists Below Treeline (human triggered avalanches unlikely) Below Treeline.
Sundays major wind event created a wind slab problem in lee (down wind) areas at Treeline and Alpine environments. The snowpack is extremely well consolidated as a result of all the moisture we have received except for the unstable wind slab problem which is anywhere from 10cm to 50 cm deep depending on aspect and exposure to wind. Unfortunately, lower elevation bands below Treeline will likely hold a good deal of dense moisture laden heavy snow from Thursdays rainfall event. The Treeline and Alpine environments, despite holding good snow could also present wind slab and storm slab potential. The forecast predicts up to 30cm/1 foot of new snow or more each day. The strong rates of precipitation, coupled with elevated wind speeds may cause wind slab and storm instabilities at Treeline and Alpine elevation bands.
|Surface||10cm - 50 cm of wind driven wind slab (soft slab to hard slab) snow is bonding poorly to crust below|
|Upper||Well bonded upper snowpack, extremely dense and moisture laden (rounding)|
|Mid||Well consolidated - 2 laminated crusts (down 60cm) and (down 120 cm) are reactive to testing but well bridged by rounded upper snowpack|
Extreme snow transport took place (Sunday) and contributed to major leeward (down wind) loading on Northerly aspects. There exists anywhere from a 10cm - 50cm of storm/wind slab upper snowpack which sits on a rain crust from (Jan 23rd) rain event. This storm/wind slab interface is reactive and is a major reason for our Considerable Avalanche Hazard Rating for the Alpine elevation band.
Monday 10 - 50 cm, Winds Moderate from the South East, Freezing level 1000 meters.
Tuesday 5 - 20 cm, Winds Light from the South East, Freezing level 1350 meters.
Wednesday 10 - 40 cm, Winds Light to Extreme from the South, Freezing level 1400 meters.
Posted on Monday January 27, 2020 by Ryan Shelly