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Avalanche Forecast

Archived

Dec 14th, 2019–Dec 15th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Cariboos.

Improving visibility beckons us into the alpine, but we need to watch for fresh slab formation as northwest wind picks up Sunday. At and below treeline, 20 to 30 cm of storm snow rests on surface hoar which teeters on the brink of becoming a touchy storm slab problem.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

We’re entering a rather quiet period with no significant snow expected until Monday afternoon. The next 48 hours are marked by seasonally normal temps, potentially sunny periods and a bit of northwest wind at ridgetop.

SATURDAY NIGHT: Freezing level at valley bottom, moderate northwest wind largely confined to the high peaks, no significant precipitation expected.

SUNDAY: Broken cloud cover, freezing level at valley bottom, light west/northwest wind at most elevations with moderate to strong northwest wind at ridgetop, no significant precipitation expected.

MONDAY: Broken cloud cover, freezing level at valley bottom, moderate west/southwest wind, snow beginning late in the day, potential for 5 to 15 cm by Tuesday morning.

TUESDAY: Overcast, freezing level beginning at valley bottom rising to 1400 m by sundown, strong southerly wind, 2 to 10 cm expected during the day, 5 to 15 more cm possible Tuesday night.

Avalanche Summary

No new avalanche activity to report from Friday.

Reports from Thursday included sloughing and loose dry size 1 avalanches in the storm snow, as well as a persistent slab avalanche triggered remotely by a helicopter. It is important to keep in mind the potential for large, persistent slab avalanches.

Snowpack Summary

A total depth of 150-300 cm of snow sits in the alpine in central parts of the region. 15-30 cm of new snow has covered a layer of feathery surface hoar crystals that were observed at all elevations throughout the region. The new snow can be expected to gain cohesion and settle into a slab in the mild temperatures, especially at treeline and below.

The primary layers of concern at this time are a couple of weak layers in the mid snowpack, formed in late November and early December which can be found most notably at treeline, and may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. These types of weak layers are typical failure planes, on which overlying slabs can start to slide and produce avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.