Avalanche Forecast

Issued: Jan 17th, 2018 5:18PM

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

cgarritty, Avalanche Canada

South Rockies.

Fresh wind slabs are set to form over a new weak layer on Thursday. Natural wind slab releases could provide ample triggers for deeper persistent weak layers.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Wednesday night: Scattered flurries bringing 2-4 cm of new snow. Strong to extreme southwest winds.Thursday: Cloudy with continuing flurries bringing 5-7 cm of new snow. Strong to extreme southwest winds. Freezing level to 1700 metres with alpine high temperatures around -2.Friday: A mix of sun and cloud. Moderate to strong southwest winds. Freezing level returning to near surface with alpine high temperatures of -6.Saturday: Mainly cloudy. Moderate west winds. Alpine high temperatures of -7.

Avalanche Summary

Large persistent slab avalanches were observed north of Sparwood (see the report here), which likely occurred over the weekend. Otherwise, limited reports suggest wet loose avalanches have been running in steep solar terrain and small thin wind slabs (size 1-1.5) releasing in alpine terrain.

Snowpack Summary

Light new snow amounts forecast for Wednesday night will begin to cover both a new layer of feathery surface hoar that has been developing in sheltered areas as well as sun crust on solar aspects. Recent warm temperatures formed this crust and also worked to settled the upper snowpack. Strong winds from the past few days have scoured windward slopes and formed new wind slabs in lee terrain at higher elevations. Wind direction has been variable but predominantly from the southwest.An unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations. Slabs can fail easily on this layer, either naturally or with the weight of a person or machine. Deeper in the snowpack, an early-season rain crust and sugary facets exist. An avalanche in motion could step down to these deeper layers, creating a large and destructive avalanche. Although the snowpack structure is variable across the region, these persistent slab problems are generally widespread. Snowpack depths are across the region are similarly variable, but typically shallower in the east.

Problems

Persistent Slabs

Large avalanches may be triggered on a number of buried weak layers, even in fairly dense trees and shallow slope angles. Stress on deep weak layers will increase as new snow and wind load the snowpack on Thursday.

Stick to simple terrain and be aware of what is above you at all times.Back off if you encounter whumpfing, hollow sounds, or shooting cracks.Avoid open slopes and convex rolls where buried weak layers may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Wind Slabs

New snow and wind will build fresh wind slabs over a new weak layer on Thursday, and older wind slabs already exist on a range of aspects at higher elevations. A wind slab release may have the force needed to trigger a deeper persistent weak layer.

Use ridges or ribs to avoid pockets of wind loaded snow.Be extra cautious as you transition into wind affected terrain.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 1.5

Valid until: Jan 18th, 2018 2:00PM