Sea To Sky

Friday will be a day of change as a powerful storm hits the coast and intensifies by the afternoon. Heavy snow and extreme winds will increase hazard to HIGH in the Alpine by day's end & possibly at treeline. Don't get overcommitted. Avoid steep terrain and overhead hazard.

Stormy weather continues through the weekend with heavy precipitation, fluctuating freezing levels and very windy double systems for Friday and Saturday. In general, highest snowfall amounts will be experienced near Brohm Ridge and taper for the mountains to the north.

Thursday night: Mainly cloudy with isolated flurries, trace amounts of new snow to 10cm near Brohm Ridge, moderate southwest winds, alpine low -7 C, freezing level 900m. 

Friday: Snow with 20-50cm new snow (highest near Brohm ridge and tapering north), wind increasing to strong to extreme southwest, alpine high -3 C, freezing level 1100m. A strong frontal passage will deliver gusty winds and potentially very extreme winds in the afternoon and bands of intense precipitation.

Saturday: Mainly cloudy, then snow increasing throughout the day with another 40-50cm, moderate to extreme southwest ridgetop winds, alpine high -2C, alpine low -8C, freezing level 1200 m rising to 2200 overnight..

Sunday: Heavy snow early in the morning with 20-40cm, strong to extreme southwest ridgetop wind easing to moderate, alpine high +1C, alpine low -7 C, freezing level 2200 m dropping to 1000m.

Thursday saw numerous explosive triggered small and large avalanches, some that released on the persistent crust layer while others were within the storm snow.

On Wednesday there were reports of ongoing avalanche activity from explosive control and human triggered avalanches in the small to large range. Reports iindicate varied reactivity on a buried crust layer and include an explosive controlled large avalanches (size 2-2.5) on lee sides of ridge top features near treeline. Elsewhere avalanches were small (size 1) with average crown depths of 5-15cm deep.

This MIN from the hanging lake area reports a remote avalanches large (size 2) avalanche at treeline at 1500m that released a slab 35cm deepen a weak layer associated with a crust.

This MIN from Wednesday in the Blackcomb backcountry reports an avalanche (size 1.5) skier controlled on a 50cm thick windslab on a NW slope in the alpine. This kind of avalanche activity illustrates how reactive wind slab avalanches can be during periods of strong wind and that they don't always fail on known weak layers (like crusts) but instead on density or crystal differences within recent snow. 

Where no slab properties are found, loose dry sluffing is being reported in steep terrain to size 1.

Have you been out and about in the mountains? If so please submit your observations to the Mountain Information Network (MIN). It doesn't have to be technical - photos are especially helpful! Thank you so much for all the great MINs submitted so far! 

As new snow begins to accumulate, be on the look out for how new and recent snow is bonding to storm interfaces and known weak layers (such as the crust and surface hoar). Significant amount of snow are forecast to begin falling on Friday in the region and accumulations of 30-50cm are forecast by midnight.Highest amounts are forecast for Brohm Ridge and will taper to the North. 

New snow is forecast to fall with strong to extreme southwestern winds. Recent snow is heavily wind affected from strong to extreme northeast, east, south and southwest winds resulting in variable distribution of snow across the alpine and ridgecrests at treeline. In lee areas expect to find wind slabs and heavier snow fall accumulations. On windward slopes sastrugi, scoured areas and old surfaces may be encountered.

In wind sheltered areas, new snow has fallen on a variety of surfaces. Most notable is the melt-freeze crust from the first week of December and in some places a buried surface hoar layer. The surface hoar is more likely preserved in sheltered locations at treeline below around 2100m.  

In the Round Mountain area, this MIN reports a "very easy" rutschblock test result (with a great photo) on 35cm over the rain crust 15 1550m at a treeline location & a moderate "sudden-pop" result with a test pit at a lower location. In the Flute zone at 200m adjacent to the Whistler resort this MIN repots "Easy-Sudden Drop" results in a test pit on a storm slab and above the crust. Nearby on Encore ridge, this MIN reports considerable wind loading with southern strong winds.

Snowpack depths change rapidly with elevation, with 20-50 cm below treeline and 150- 170cm in the alpine. Below treeline conditions are slowly improving but remain variable as indicated in this MIN from Singing pass trail.  

• Watch for changing conditions today, storm slabs may become increasingly reactive.
• Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
• Avoid freshly wind loaded terrain features.
• Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.