Avalanche Forecast

Issued: Jan 30th, 2019 6:15PM

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

Avalanche Canada ghelgeson, Avalanche Canada

Watch for the development of shallow storm slabs and fast moving loose dry avalanches as storm totals stack up Thursday. A natural cycle may be underway by Thursday night as the storm snow overwhelms the widespread buried surface hoar.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Thursday kicks off a multi-day snow event that should provide a nice re-set for the region. This is a dynamic period as northwest flow scoops up incoming weather systems off the east-pacific and directs them over the province. Take these snow totals with a grain of salt, amounts are changing quite drastically from one model run to the next. WEDNESDAY NIGHT: Freezing level near valley bottom, light variable wind at most elevations with strong northwest wind at ridgetop, 1 to 5 cm of snow possible.THURSDAY: Overcast, freezing level near valley bottom, light south wind at most elevations with strong west/southwest wind at ridgetop, 5 to 15 cm of snow possible during the day, 10 to 30 cm possible Thursday night.FRIDAY: Overcast, freezing level at valley bottom, light southwest wind at most elevations with strong southwest wind at ridgetop, 10 to 15 cm of snow.SATURDAY: Broken cloud cover, freezing level at valley bottom, moderate to strong southwest wind, 1 to 5 cm of snow possible.

Avalanche Summary

On Tuesday reported avalanche activity was limited to a size 2 cornice failure above a southeast facing slope at 2500 m. No new avalanche activity reported on Monday. On Sunday cornice failures to size 1.5 were observed on north through east facing terrain around 2000 m. Small natural wind slab avalanches to size 1 were reported on east and northeast facing terrain between 2000 and 2300 m.On Saturday a skier triggered a small persistent slab avalanche on an east facing feature at 2000 m, failing on the mid-January surface hoar.

Snowpack Summary

Saturday delivered warmth and wind to the region, followed by 10 to 15 cm of new snow and a very strong wind event on Sunday. This MIN report provides a good description along with some photos that encompass conditions Sunday. The weekend weather left a crust on steep south facing aspects and redistributed quite a bit of snow into potentially deep wind slabs in lee features at and above treeline. These wind slabs have grown old and tired, and are probably only susceptible to triggering in extreme terrain. 15 to 45 cm of snow continues 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 1500 and 1800 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

Storm Slabs

An icon showing Storm Slabs
Incoming storm snow is unlikely to bond well to the old surface which is a mix of sastrugi, stubborn old wind slabs, facets, crust and surface hoar. Watch for fast moving sluff and touchy small slabs as storm snow stacks up Thursday.
Watch your sluff: it may run faster and further than you expect.Watch for larger than expected storm slabs due to the presence of buried surface hoar.Conditions are expected to deteriorate throughout the day.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 1.5

Persistent Slabs

An icon showing Persistent Slabs
15 to 45 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 at and below treeline.
Use extra caution around steep open terrain features, such as cutblocks, gullies and cutbanks.Avoid convex rolls at and below treeline where buried surface hoar may be preserved.Surface hoar distribution is highly variable. Avoid generalizing your observations.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Jan 31st, 2019 2:00PM

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