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Archived

Avalanche Forecast

Dec 31st, 2017–Jan 1st, 2018
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Lizard-Flathead.

We're into a tricky period as a critical amount of storm snow settles (into a slab) and sits on a buried weak layer. Keep your terrain choices on the conservative side until conditions stabilize.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Dry with gradually warming alpine temperatures during the week. Cold in the valley bottoms. MONDAY: Mix of sun and cloud. Ridge wind light southwest. Temperature -12. Freezing level surface.TUESDAY: Mix of sun and cloud. Ridge wind light west. Temperature -10. Freezing level surface.WEDNESDAY: Mostly sunny. Ridge wind light southwest. Temperature -8. Freezing level surface.

Avalanche Summary

On Sunday, an explosives-triggered Size 2.5 persistent slab avalanche was reported on a south east aspect at 1700m near Fernie, running on the mid-December surface hoar layer (down 65cm in that location). A widespread natural avalanche cycle occurred on Friday into Saturday producing storm slab avalanches to Size 2 on north through south easterly aspects between 1700 m and 2100 m.A surprising amount of natural avalanche activity was also reported below treeline on Saturday - see here for the MIN report and details. On Thursday, natural and skier triggered storm slab releases up to size 1.5 were reported including a remote-triggered Size 1.5 slab on an open, rock slope on a north west aspect below treeline. Whumpfing and cracking in rocky areas was also reported on Thursday. See the report on the Mountain Information Network (MIN) here.

Snowpack Summary

On Friday into Saturday, 20-35 cm of storm snow fell on top of 25 cm of previous very low density storm snow. Winds (at times strong from the south west) have modified the snow pack, creating an "upside-down" storm slab layer with stiffer snow on top of softer snow.This upside-down storm snow layer overlies roughly 50 cm of old storm snow from last week that formed into stiff wind slabs in exposed terrain near ridge top, but remains low density in sheltered areas. The mid-December layer is now buried 60-80 cm below the surface. The layer includes crusts on south and west facing slopes and feathery surface hoar in sheltered areas at and below treeline, and has been producing moderate, sudden results in recent snowpack tests.The lower snowpack is generally well settled with a thick prominent crust that was buried near the end of November.

Avalanche Problems

Storm Slabs

Reactive storm slabs have been reported at all elevations, and are sensitive to both natural and human triggers.
Choose conservative lines with low consequence and avoid overhead hazard.Be aware of the potential for reactive storm slabs at lower elevations, even on small features.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 3

Persistent Slabs

A weak layer composed of surface hoar and/or crusts is buried 60-80 cm below the surface.
Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.Choose well supported terrain without convexities.Watch for whumpfing, hollow sounds, and shooting cracks.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3