Avalanche Forecast

Issued: Apr 6th, 2014 10:12AM

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

swerner, Avalanche Canada

Northwest Coastal.

Monday's storm will pack a punch and is driving the Danger Ratings. The snowpack does not typically handle rapid change well and deeply buried persistent weak layers may re-awaken.

Summary

Confidence

Good

Weather Forecast

Starting tonight an intense, direct frontal system will slam the North Coast bringing heavy precipitation, rising freezing levels and strong to extreme southerly winds.Sunday night: Freezing levels rising to 800 m and expecting 10-40 cm at higher elevations (higher value indicated for coastal areas). Ridgetop winds generally moderate from the south with strong gusts. Monday: Freezing levels rising to 1700 m and expecting up to 50 mm in coastal areas and up to 30 mm further north (Bear Pass, Stewart, etc.). Ridgetop winds strong from the south gusting to extreme values. Tuesday: Freezing levels falling to 800 m or lower. Precipitation amounts 10-20 mm in coastal areas with lower amounts near 10 mm as you move inland.Wednesday: Snow accumulations 10-20 cm. Ridgetop winds moderate from the west. Freezing levels near 1000 m.

Avalanche Summary

On Saturday, numerous loose wet avalanches occurred below 1200 m. Most operators had limited observations due to poor visibility. The recent storm snow has shown a fairly poor bond to the older snow surfaces. Natural loose dry and wet avalanche activity up to size 2 was reported on Friday. Expect a widespread natural avalanche cycle at all elevations on Monday. It will take a couple of days before things start to settle out. Travel in avalanche terrain is not recommended.

Snowpack Summary

An additional 10-40 cm of snow at upper elevations is forecast, followed by heavy precipitation on Monday. The snowpack will be under the influence of direct rapid change, and will become weak and unstable. This additional load will fall onto a mix of surface hoar, facets, melt freeze crusts and firm wind pressed snow and will likely have a poor bond. Storm and wind slabs will form, especially at upper elevations. Lower elevations the snowpack will likely become saturated adding to the already isothermal conditions.Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm and is composed of facets/surface hoar on shady aspects and facets/crust on southerly aspects. The early February crust/facet/surface hoar combo is down 150 - 200cm. This layer was responsible for a couple of unexpected large avalanches right at the end of March and the beginning of April. These layers should be on your radar and could become reactive with intense loading from rain/snow, warm temperatures and strong winds.

Problems

Storm Slabs

New snow driven by strong ridge top winds will likely create touchy slabs at and above treeline. This snow adds to existing storm snow and is expected to be unstable initiating large-very large avalanches.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 5

Deep Persistent Slabs

Two buried weak layers exist in the snowpack. These weak layers could be activated by cornice fall, a surface avalanche in motion, or intense loading from snow, rain and wind. Avalanches failing on these weak layers will be large and destructive.

There is potential for large, deep avalanches due to the presence of buried facets and surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 7

Wet Slabs

At lower elevations the snowpack will likely become saturated and weak with heavy rainfall. Wet slab avalanches typically move slower, however they are very destructive and can mow down anything in their path.

Avoid run-out areas, road cut banks and steep slopes at treeline and below. Indicators of the snowpack becoming moist or wet is snowballing, larger pinwheels and of course natural avalanche activity. >Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Apr 7th, 2014 2:00PM