Avalanche Forecast
Sea To Sky
Thursday's storm came in with strong to extreme southerly winds that formed deep wind slabs on top of buried surface hoar, facets and crust. It may be calendar spring, but it's winter in the mountains, be very cautious in wind affected terrain.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- There is potential for wide propagation, fresh slabs rest on buried surface hoar, facets and crust.
- Minimize exposure to sun exposed slopes if solar radiation becomes strong.
- Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.
Avalanche Summary
Observations from Thursday are limited due to poor visibility and travel during the storm. There was likely natural avalanche activity that would have been most prevalent at upper elevations. Explosive control work produced storm slab avalanches to size 1.5 Thursday morning, but that was before the bulk of the snow fell.
We received a great MIN report early Thursday afternoon that talked about shooting cracks in the storm slab that were traveling for several meters. More details here.
There was a rather anomalous size 3.5 that was seen on the Cheakamus Glacier from Whistler March 15th. We don't have details on the failure plane of this avalanche, but it may have run on the mid-February crust.
Snowpack Summary
Thursday and Friday's storm snow delivered 10 to 40 cm of snow accompanied by strong to extreme wind out of the southwest, south and southeast. Storm slabs on immediate lee features at ridgeline may be up to 70 cm in depth. These slabs rest on a mix of moist grains at low elevations, crusts on solar aspects at all elevations and surface hoar/facets on north/east facing features at treeline and Alpine elevations. Some west facing features may have surface hoar on top of a crust which would be particularity problematic. The storms transition from warm to cold should be good for our snowpack in the long term, but this weekend touchy storm slabs are likely widespread.
A crust from mid-March is now down 15 to 60 cm below the surface. This crust is prevalent everywhere with the exception of high elevation north aspects.
60 to 140 cm below the surface is a combination of facets, surface hoar, and/or crust known as the mid-February layer. This interface has not been active recently, but it does continue to produce resistant planar results in snowpack tests.
The mid and lower snowpack is strong and well settled.
Weather Forecast
A cold unstable pool of air is allowing for cooler than normal temperatures and also driving convective precipitation that should continue through Friday night. A bit of clearing is in store for Saturday before cloud builds back into the region Sunday.
FRIDAY NIGHT: Freezing level around 500 m, moderate south/southwest wind, 1 to 5 cm of snow.
SATURDAY: Partly cloudy, freezing level beginning at 500 m rising to 1000 m, light variable wind, no significant precipitation expected.
SUNDAY: A few clouds in the morning building to broken cloud cover in the afternoon, freezing level holding at about 800 m, light west/southwest wind, no significant precipitation expected.
MONDAY: Overcast, freezing level beginning around 600 m rising to about 1100 m, light southwest wind at 2000 m, moderate to strong west wind at ridge top, 2 to 4 mm of precipitation possible.
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Thursday's storm came in with strong southerly wind that has formed slabs up 70 cm in depth on lee alpine features. Storm slabs likely remain sensitive to human triggering. Periods of sun may also induce natural avalanche activity on solar aspects.