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Avalanche Forecast

Archived

Nov 29th, 2019–Nov 30th, 2019

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

Regions

Purcells.

Where there is enough snow to recreate, the snowpack is highly variable. The most likely place to trigger an avalanche is where the wind has formed slabs at higher elevations.

Share what you see in the mountains this weekend via the MIN!

Confidence

Moderate - Confidence is due to a stable weather pattern; little change is expected for several days. Uncertainty is due to the limited number of field observations. Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Friday night: Few clouds, light easterly wind, alpine temperature -12 C, no precipitation.

Saturday: Mostly sunny, light variable wind, alpine temperature -9 C, no precipitation.

Sunday: Mix of sun and cloud, light southwest wind, alpine temperature -7 C, no precipitation.

Monday: Mostly cloudy, west wind increasing to moderate, alpine temperature -8 C, isolated flurries with 1-3 cm of accumulation possible.

Avalanche Summary

There have been reports of human and explosive-triggered avalanches on north-facing alpine terrain in the past few days releasing to the ground. The most likely place to trigger avalanches is where the wind has drifted snow into slabs in the alpine. This is a great MIN report from the neighboring South Columbia region that helps to paint the picture of these wind slab avalanches.

Observations are limited this time of year, so there is a fair bit of uncertainty about the extent of current avalanche activity. If you see anything while out in the field, please consider sharing that information with us and the backcountry community via the Mountain Information Network.

Snowpack Summary

With this week's clear and cold weather, last weekend's storm snow is losing strength, except where it has been drifted into wind slabs in the alpine. Variable winds previously redistributed the 10-30 cm of recent snow into wind slabs that may still be possible to trigger. These slabs could be more reactive where they overlay a weak layer of surface hoar (feathery crystals). With few field observations and substantial spatial variability, uncertainty exists as to the distribution and reactivity of these layers. 

Snowpack depth is highly variable, ranging from 10 cm to 100 cm. Expect to find weak facets (sugary, cohesion-less snow) in the thin areas. Elsewhere, you may find a melt-freeze crust from late October above faceted snow near the base of the snowpack. There's a great summary of conditions in Golden after last weekend's storm here.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.