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Avalanche Forecast

Archived

Mar 24th, 2018–Mar 25th, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Sea To Sky.

Thursday's storm came in with strong to extreme southerly winds that has formed storm slabs on top of buried surface hoar, facets and crust. Be very cautious in wind loaded terrain where these slabs may be surprisingly deep.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SUNDAY: Increasing cloud and flurries in the afternoon. Accumulation trace. Ridge wind light, southwest. Alpine temperature near -10. Freezing level 800 m.MONDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind light southwest. Alpine temperature near -5. Freezing level 1200 m.TUESDAY: Cloudy, flurries. Accumulation 5-15 cm. Ridge wind moderate, west. Alpine temperature near -1. Freezing level 1700 m.

Avalanche Summary

Saturday we received reports of a natural avalanche cycle from size 2-3 that occurred during the storm in wind loaded and cross-loaded alpine terrain.On Friday explosive control work and ski cutting produced numerous storm slab results from size 1.5-2, as well as size 2 cornice results and few remote/sympathetically triggered size 1.5 releases. Crown depths generally ranged from 20-40 cm deep, although up to 60 cm in loaded alpine areas.There was also a report of a skier triggered size 1.5 on Friday that surprised a group on a convex feature at treeline. Read MIN reportWe 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.

Snowpack Summary

Thursday and Friday's storm snow delivered 20 to 50 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 60 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.A crust from mid-March is now down 40 to 60 cm below the surface. This crust is prevalent everywhere with the exception of high elevation north aspects.80 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 are strong and well settled.

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.