Avalanche Forecast

Issued: Dec 10th, 2014 8:41AM

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

rbuhler, Avalanche Canada

Purcells.

The warm, wet, windy storm continues. Backcountry ski conditions are reported to be terrible and avalanche hazard remains elevated. Now is a good time for indoor activities or take your rain gear with you to your local ski hill.

Summary

Confidence

Fair - Timing of incoming weather systems is uncertain

Weather Forecast

The sub-tropical storm system continues to produce similar weather conditions on Thursday. Freezing levels will be around 2000m, alpine winds should remain strong, and we can expect another 5-15mm of precipitation. Things start to change on Friday as freezing levels should drop below 1500m and alpine winds ease during the day. Lingering precipitation is expected on Friday with amounts around 2-4mm. A ridge of high pressure is expected to begin to build on Saturday resulting in a mix of sun and cloud. Freezing levels are expected to be back down near valley bottom and winds should be calm or light.

Avalanche Summary

Reports from Wednesday includes natural loose wet avalanches up to size 1.5 from steep terrain up to 2200m and explosive triggered slab avalanches up to size 2.5. These slabs are typically around 20cm thick. I expect as more snow accumulates in the alpine and the slab gets thicker, we should start seeing natural storm slab avalanches, especially from the more wind loaded areas.

Snowpack Summary

Rain to high elevations is expected to be saturating the upper snowpack. A wet snow surface is expected up to 2000m elevation and moist snow to around 2400m. Strong winds are loading leeward features in the alpine. Below the new storm snow may be a layer of surface hoar which was buried on Dec 5. Another 15-20cm below this you may find a hard rain crust. In the Golden area this crust exists up to around 1600m, whereas in the south it is up to 2000m or higher. Deep in the snowpack you may find the mid-November weak layer (surface hoar, facets, and/or a crust) and/or a faceted rain crust from early November. The reactivity of these layers may be slowly diminishing, but they still warrant cautious consideration. In some areas that already avalanched, the new storm snow may be sitting on a thick layer of facets that are sitting on the ground.

Problems

Storm Slabs

Storm slabs will continue to build at higher elevations as the storm progresses. Strong winds will quickly reload leeward features.

Minimize overhead exposure; avalanches triggered by windloading may reach run out zones.>Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Likelihood of triggering a deep weak layer is expected to increase with new storm loading and warming. Any slopes that did not avalanche during the last storm cycle should still be considered hazardous. Smaller avalanches may trigger a deep release.

Avoid common trigger zones including thin snowpack areas, near rocky outcrops, and steep alpine slopes.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Loose Wet

Rain at lower elevations will reduce the stability of the upper snowpack and loose wet avalanches are expected in steep terrain.

Avoid areas with steep overhead hazard.>Be cautious of sluffing in steep terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Dec 11th, 2014 2:00PM