Avalanche Forecast

Issued: Dec 28th, 2017 4:58PM

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

jmcbride, Avalanche Canada

South Rockies.

With snow and wind in expected Thursday night and Friday, watch for fresh wind slabs to develop in open areas. If triggered these slabs may step down to a deeper layer.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY NIGHT: Snow. Accumulation 10-15 cm. Ridge wind light southeast possibly strong at times. Temperature -22. Freezing level surface.FRIDAY: Cloudy, snow developing and overnight. Accumulation 10-20 cm. Ridge wind light northeast possibly strong at times. Temperature -22. Freezing level surface.SATURDAY: Mix of sun and cloud, flurries. Accumulation 5-10 cm. Ridge wind light southwest. Temperature -20. Freezing level surface.SUNDAY: Mostly sunny. Ridge wind light southwest. Temperature -14. Freezing level surface.

Avalanche Summary

Limited reports suggest triggering slab avalanches remains possible. Two skier triggered avalanches have been reported east of the divide the past few days. One was a small wind slab triggered in a steep gully and the other was a larger persistent slab (size 2) triggered low on a slope that propagated up and across the slope on a 50 cm deep crust. The later highlights the potential for persistent slab avalanches to have wide propagations.

Snowpack Summary

Up to 10 cm of new snow fell overnight Wednesday and during the day on Thursday and overlies up to 60 cm of old storm snow in southern and eastern parts of the region and 30 cm in the Elk Valley. Wind has formed harder wind slabs in exposed terrain, but low density storm snow remains in sheltered areas.The main question in the snowpack surrounds the mid-December layer sitting beneath the recent snow. This layer includes crusts on solar aspects and feathery surface hoar in sheltered terrain at and below treeline, and has produced whumpfing as well as moderate, sudden results in recent snowpack tests. The lower snowpack is composed of mostly soft sugary snow and a few early season crusts that have not produced significant test results recently.For an update on recent conditions check out the Mountain Information Network (MIN) report here. And please post your own reports!

Problems

Wind Slabs

Expect fresh wind slabs to develop throughout the day on the downwind sides of ridges and gullies.

Avoid freshly wind loaded features.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered, wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

A weak layer composed of surface hoar and/or crusts is buried 40-80 cm below the surface. Triggering an avalanche on this layer is possible in areas where the snow has settled into a cohesive slab.

Choose well supported terrain without convexities.Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.Watch for signs of instability such as whumpfing, or cracking.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Dec 29th, 2017 2:00PM