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Avalanche Forecast

Archived

Mar 15th, 2014–Mar 16th, 2014

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

Regions

South Columbia.

A conservative approach is critical as Sundays storm increases the load on a variety of weak layers in our complex snowpack.

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain on Sunday

Weather Forecast

Synopsis: Snow should start falling in earnest around supper time Saturday evening. Look for it to snow through Sunday night accompanied by strong SW winds. In the wee hours of Monday morning the flow begins to take a more northwesterly tilt which eventually leads to ridging and clearing on Monday/Tuesday. Saturday Night: Freezing Level: 1400m - 1900m; Precipitation: 6:12mm - 6:20cm; Treeline Wind: Moderate, SW | Extreme SW at ridgetop.Sunday: Freezing Level: 1300m - 1800m; Precipitation: 3:8mm - 4:15cm; Treeline Wind: Moderate, SW | Strong SW at ridgetop.Monday: Freezing Level: 1200m; Precipitation: 0:3mm - 0:5cm; Treeline Wind: Light, NW | Moderate NW at ridgetopTuesday: Freezing Level: 1500m; Precipitation: Nil; Wind: Light, SW

Avalanche Summary

On Friday we received a report of storm snow failing as a fast moving size one avalanche that ran on the March 13th crust on a steep north facing slope at treeline. There was also a report of a size two avalanche that was triggered accidently on a North facing slope, again at treeline, on the early March surface hoar/crust combo. On Thursday explosive control produced avalanches to size 3 on both SE & NE facing slopes in upper treeline and alpine elevations. A skier remote triggered a size 3 avalanche from 100m away on a NE facing slope at 2200m. The avalanche was triggered from low angle terrain and resulted in a very large avalanche with a crown up to 150cm in depth. Last Saturday's avalanche fatality occurred in the Keefer Lake area northeast of Cherryville. The avalanche, which occurred in a cut block at about 1700m, involved 3 sledders who were in a party of 6. Two of the men were able to inflate their airbags and were partially buried. The deceased was reportedly not able to inflate his airbag, and was buried approximately 5m below the surface.While not in this region, it's worth taking a look at last weekends incident from the Cariboos.

Snowpack Summary

The surface is currently a mix of 3 - 6mm surface hoar and crust. Last weeks storm snow has settled into a 50 - 100 cm slab that rests on the early March interface consisting of small grained surface hoar in sheltered areas and a sun crust on solar aspects. In upper elevation wind exposed terrain the new snow has been pushed into deep wind slabs by moderate SW winds.The last week featured an average daytime freezing level around 1800m which resulted in a daily melt freeze cycle that left many features wet and sloppy by the afternoon. This setup resulted in some serious incidents recently.Ridgetop cornices remain large and unsupported.The February 10th surface hoar/facet/crust combo is 80cm - 250cm below the snow surface and widespread throughout the region. Surface avalanches in motion and cornice fall still have the potential to initiate an avalanche on this deeply buried weak layer. Remote triggering on this layer is ongoing. The mid and lower snowpack are strong and well consolidated.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.