Avalanche Forecast

Issued: Feb 8th, 2016 8:38AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Persistent Slabs, Loose Wet and Storm Slabs.

jlammers, Avalanche Canada

Northwest Coastal.

Recent storm loading, buried weak layers, high freezing levels and solar radiation are a perfect recipe for widespread avalanche activity on Tuesday.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Tuesday

Weather Forecast

On Tuesday expect mainly clear skies, moderate southwest ridgetop winds and freezing levels around 3000m. On Wednesday and Thursday the region should see light snowfall (3-5cm each day), strong southwest winds and freezing levels at about 1700m.

Avalanche Summary

On Saturday explosives control in the Stewart and Ningunsaw areas produced deep persistent and storm slab avalanches in the size 2.5-3 range. While most avalanches observed failed within recent storm layers, a few failed on basal facets in shallow snowpack parts of the region. There was also a recent size 3 natural persistent slab avalanche north of Stewart. This avalanche failed on the January 9th surface hoar.Closer to Terrace, a few recent storm slab avalanches to size 3 were observed between 1200 and 1700m. A skier also triggered a size 1.5 wind slab avalanche on a southwest aspect at 1450m. The skier was not injured.I'm sure there was a decent round of storm slab activity on Sunday and Monday in response to new snow and wind. Looking forward, solar radiation and skyrocketing freezing levels will spark a widespread round of loose wet avalanche activity. Warming will also promote cornice falls, wet slabs and persistent slab avalanches failing on deeper, more destructive weak layers.

Snowpack Summary

On Sunday a warm, wet and windy storm added mass and reactivity to recently formed storm slabs. 24 hour snow totals were around 40cm in the Terrace area with closer to 70cm falling in the mountains around Stewart. Rain on Monday, and then rising freezing levels and solar radiation will likely leave most surfaces moist or wet on Tuesday. This warming will also have a significant destabilizing effect on the snowpack. The January 9th surface hoar/facet layer is down 70-200 cm and remains a concern, especially with heavy and/or thin-spot triggers. Around the same depth you may also find a surface hoar/facet interface from around New Years. There continues to be a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem; however, forecast warm temperatures and solar radiation will increase the likelihood of triggering these layers where they still exist. A very conservative approach to mountain travel is still required.

Problems

Persistent Slabs

Recent storm loading, solar radiation and skyrocketing freezing levels will increase the likelihood of waking-up deep and destructive persistent weak layers. Cornice falls triggered by solar radiation may also trigger a persistent slab avalanche.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Be aware of thin areas that may propogate to deeper instabilites.>Do not travel on slopes that are exposed to cornices overhead.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 6

Loose Wet

Rising freezing levels and solar radiation on Tuesday will spark a round of loose wet avalanche activity on sun-exposed slopes. Loose wet avalanches may also step down to deeper, more destructive layers.

Stick to non-avalanche terrain or small features with limited consequence.>Be cautious of wet sluffing in steep terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Storm Slabs

Heavy storm accumulations may remain sensitive to human triggering on Tuesday. Watch for increased reactivity in high elevation lee terrain.

Be alert to conditions that change with elevation.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Feb 9th, 2016 2:00PM