Avalanche Forecast

Issued: Jan 28th, 2019 4:20PM

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

ghelgeson, Avalanche Canada

North Columbia.

Manage wind slabs by paying attention to how the snow feels underneath your skis/track, and backing off where it feels stiff. Increase your caution at and below treeline, buried surface hoar has been especially touchy between 1400 & 1900 m.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

High pressure, cold temperatures and clear skies should allow for great travel and visibility Tuesday. Cloud cover starts to build back in Wednesday ahead of two storm pulses that should deliver a bit of snow beginning on Friday.MONDAY NIGHT: Freezing level at valley bottom, light northerly wind, no precipitation expected.TUESDAY: Clear skies, freezing level at valley bottom, light variable northerly wind, no precipitation expected.WEDNESDAY: Broken cloud cover, freezing level at valley bottom, mostly light variable wind with moderate to strong northwest wind at ridgetop, trace of snow possible.THURSDAY: Overcast, freezing level at valley bottom creeping up towards 800 m in the afternoon, light variable wind, 1 to 5 cm of snow possible.

Avalanche Summary

On Sunday wind slabs failed naturally to size 2.5 on northwest, northeast, east, southeast and south facing aspects between 1900 and 2800 m. Persistent slab avalanches failing on the mid January Persistent Weak Layer (PWL) were widespread to size 1.5 on all aspects between 1500 and 1900 m.There were a few reports of remote triggering Friday on north, northwest and east facing slopes. One was triggered from a flat ridge 30 m away from the avalanche which ran on a moderately inclined north facing slope at 1900 m producing a size 2.5 avalanche. Last week storm and persistent slab avalanches averaging size 2 released naturally and were human triggered on the mid-January surface hoar. The majority of these avalanches occurred at treeline and below, however, a few were noted at higher elevations in the alpine.

Snowpack Summary

Saturday delivered warmth and strong to extreme wind out of the west, south, southwest and northwest. This left a crust on steep south facing aspects and redistributed quite a bit of snow into wind slabs in lee features at and above treeline. The warmth also allowed 25 to 50 cm of snow to continue to consolidate above the mid-January persistent weak layer (PWL). This PWL is made up of large surface hoar that is most prevalent at and below treeline, with enhanced reactivity noted between 1400 and 1900 m. On steep solar aspects this interface presents as a crust, there may be locations where the surface hoar actually sits on the crust.The middle and lower portions of the snowpack are generally well-settled and strong.

Problems

Persistent Slabs

25 to 60 cm of snow sits above a weak interface of surface hoar and crust. The recent warm to cold temperature transition has allowed a more cohesive slab to form above the surface hoar which is most prevalent between at and below treeline.

Take heed of obvious signs of instability such as whumpfing, shooting cracks and recent avalanches.Avoid convex rolls at and below treeline where buried surface hoar may be preserved.Use extra caution around steep open terrain features, such as cutblocks, gullies and cutbanks.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Wind Slabs

Wind Saturday night into Sunday was out of the west, south, southwest and northwest with more than enough oomph to form wind slabs. These wind slabs may rest on a crust, or perhaps even buried surface hoar near treeline.

Be careful around freshly wind loaded features, especially near ridge crests and roll-overs.Avoid areas where the snow feels stiff and/or slabby.Carefully evaluate bigger terrain features on an individual basis before committing to them.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Jan 29th, 2019 2:00PM