Regions
Vancouver Island.
Confidence
High- significant snowpack observations and weather forecast models in agreement.
Travel/Terrain Advice
Avoid steep loaded slopes and features with north-west aspects that gather wind transported snow. Watch new snowfall amounts over Wednesday night and use careful route finding and cautious decision making after the storm cycle. Snowpack evaluation/tests Thursday will be important information to gather if traveling in more challenging terrain.
Past Weather
Strong (up to 70k mph) winds from the south-east accompanied the new snowfall (up to 15cm) Sunday. Monday a spike in the freezing level (up to 1300m) increased temperatures and left a thin melt freeze crust on solar aspects after it pasted, in all but the alpine elevations. Late Monday into Tuesday another wave of new snow fell on the hills bringing anywhere from 12-20cms of fresh.
Avalanche Summary
Sunday avalanche control on Mt Washington saw a few very soft slab-loose avalanches on north west slopes in the treeline with ski cutting and explosives. Ski cutting in other near ski hill terrain produced numerous very small wind slab avalanches on convex unsupported ridge top features. A skier accidental in out of bounds terrain at Mt Cain (west bowl) was also was reported in the size 1.5-2 range (see incident reports section for more details). Monday ,once visibility improved, several small naturally triggered point releases were seen from steep north aspects at treeline on the back of Mount Washington (most probably running prior during Sundays storm) and one small wet slab size 1 was noted by skiers on Mt Elma ,in paradise meadows, on a open north aspect unsupported convex roll below treeline (associated with the 1300m freezing level spike no doubt). So an active three days for avalanches for the island.
Snowpack Description
Surface - Preserved new snow in sheltered zones in the treeline and below treeline elevations. Alpine and exposed treeline have stiffer wind pressed snow and ridge tops have some isolated zones of wind stripped exposed crust.Upper - New snow everywhere with a thin non-supportive crust on solar aspects, approximately 12-20 cm down on below treeline and treeline terrain from Monday's warm spike. Sunday's new snow (15-5cm) has created wind slabs (now buried) on north to west aspects in the alpine and treeline. All this new load is sitting on the January 7th rain crust and has shown significant weakness and failures in tests. Mid - The new snow and crust buried on Jan 7th is now bridging and almost eliminating concerns surrounding the mid Dec and mid Nov crusts. The moist mid snowpack seams very stable producing only hard results in tests on the Dec crust.Lower - Well settled.
Weather Forecast
Light snowfall with cloudy skies and cold temperatures Wednesday. Fallowed (Thursday) by a new storm system via moderate southeast winds, bringing snowfall amounts from 5-15cm in the north to 15-25cm for the west coast and 10-15cm for the east. Light snow at first Friday and then a trend (unfortunately) toward warming and high freezing levels for the weekend. Wed - 1-5 cm of new snow. Winds light south east to south west.Freezing levels of 140-900 mThurs - 5-25 cm of snow. Winds moderate south east. Freezing levels of 400-1000mFri - 2-7 cm of new snow. Winds light west to moderate south.Freezing levels of 0-1250 m
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.