Sea To Sky

10-30 cm of new snow & strong to extreme southern winds will have created reactive storm slabs. A small avalanche may trigger deeper weak layers. Avoid steep slopes & overhead hazard, watch for signs of instability & be cautious with wind affected snow. Caution Cornices!

Weather systems in the south coast and sea to sky area are fast moving and weather models are changing. A third significant storm is now forecast to impact the region for Sunday night into Monday and the intensity of Saturday night's storm has eased. Highest snowfall amount predicted for coastal regions (like Brohm Ridge) and taper interior (like Whistler-Blackcomb)

Friday night: Mainly cloudy with isolated flurries, 5-10cm new snow, moderate southwest winds, alpine low -7 C, freezing level 900m. 

Saturday: Mainly cloudy, with snow flurries in the late afternoon / evening, 5-10cm snow trace, moderate to extreme southwest ridgetop winds, alpine high -2C, alpine low -8C, freezing level 1200 m rising to 1500m-2000 overnight.

Sunday: Mainly cloudy with snow flurries beginning late in the day, new snow 10-30cm new snow, strong southwest ridgetop wind, alpine high +3C, alpine low -7 C, freezing level rising to 2200 m.

Monday: Heavy snow with 20-40cm new snow, strong southerly winds, alpine high -2C, alpine low -7 C, freezing level rising to 1500 m.

Friday reports of a suspected widespread natural avalanche cycle to size 2 at the peak of the intense wind and precipitation. Early morning explosive control showed explosive and intentionally triggered avalanches to size 1.5 on re-loaded crusts. These windslabs were reported in lee and cross loaded features. 

Thursday saw numerous explosive triggered small (size 1's) and large avalanches (size 2's) , some that released on the persistent crust layer while others were within the storm snow. One avalanche in particular illustrated how a small avalanche can step down to a known deeper layer creating a large avalanche.  

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. 

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! 

The main story in the snowpack is new snow falling with strong to extreme wind created rapid loading in lee features. 15-30cm of snow were forecast to fall in the sea to sky area Friday into Saturday, with snowfall amounts tapering with distance from the coast.

Remote weather stations in alpine regions showed wind with Friday afternoon's storm reaching gusts of 140km and sustained values from the south / southeast over 100km. Much of the forecast snowfall was likely blown deep into the lee features and not necessarily deposited in immediate lees.  

Investigate how wind affected snow is bonding to previous surfaces and to layers within the storm snow.

In these wind affected areas, anticipate sastrougi, hard windslabs, scouring to ground and old surfaces and heavily reworked slopes at ridgecrests. Anticipate wind affect to extend well into bowls below ridgecrests, along cross-loaded galleys and features and potentially in open areas below tree line.  

Investigate everywhere how new snow is bonding to storm interfaces and known weak layers (such as the crust and surface hoar).  

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.  

• Avoid freshly wind loaded terrain features.
• Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
• Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
• Pay attention to cornices and give them a wide berth when traveling on or below ridges.