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Avalanche Forecast

Archived

Jan 26th, 2021–Jan 27th, 2021

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

Regions

Purcells.

A dusting of flurries and increasing winds may build fresh wind slabs by the end of the day.

Confidence

Moderate - Uncertainty is due to the timing of the incoming weather system.

Weather Forecast

Tuesday night: Mostly cloudy / southeast winds, 10-25 km/h / alpine low temperature -9

Wednesday: Cloudy with isolated flurries, 5-10 cm / southeast winds, 15-30 km/h/ alpine high temperature -12

Thursday: Cloudy with isolated flurries, trace to 5 cm / southeast winds, 10-15 km/h / alpine high temperature -12

Friday: Cloudy with sunny breaks / southwest winds, 10 km/h / alpine high temperature -12

Avalanche Summary

On Sunday in Glacier National Park, a skier triggered a size 2 avalanche upon entrance into a cross-loaded terrain feature.

We're continuing to track a layer of surface hoar from early January which is trending unreactive. Two MIN reports (MIN report 1; MIN report 2) from north of the region in Hope Creek report human-triggered slab activity from January 20. This MIN report from the Quartz zone (from Jan 14) shows a reactive layer of Jan 11th surface hoar on north-facing slopes near treeline. Investigate for this layer around sheltered treeline slopes where surface hoar has been preserved. 

Following the mid-January storm, we received reports of avalanches reaching size 3 in the central part of the region, lending support to the idea that some larger releases may have involved more deeply buried persistent weak layers. Check out this MIN report from Mt McKay. Although avalanche activity on these layers from early December and November has been isolated, the possibility exists for large triggers to reactivate these deeper instabilities. 

Snowpack Summary

The snowpack boasts a variety of surfaces including scoured and pressed surfaces in exposed terrain, large cornices, isolated wind slabs, and variable wind affected and facetted snow in more sheltered terrain. Cold temperatures are encouraging surface faceting and breaking down wind slabs. A thin sun crust may be found on steep solar aspects. Recent surface hoar growth has been observed in sheltered terrain; gusty winds over the weekend likely impacted the crystals in more exposed and upper elevation areas. 

A weak of layer of surface hoar from Jan 11th is down 10-50cm. In recent snowpack tests this layer has produced sudden results at treeline elevations in areas near KHMR. This persistent weak layer is most suspect in sheltered, open slopes at treeline and warrants slope-specific investigation if you're travelling in the north of the region.

Two deeper layers of surface hoar from December 13th and December 7th may still be found down 100-150 cm. The Dec 7th weak layer consists of a combination of decomposing surface hoar with a crust and faceted snow. Avalanche activity on these persistent weak layers has dwindled in the last week, with snowpack tests results trending to resistant and unreactive. 

The lower snowpack is characterized by a notable rain crust from early November that is surrounded by a weak layer of sugary facets. It may still be possible to trigger with large loads in steep, shallow, rocky areas with a thin to thick snowpack.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Large cornice falls are dangerous on their own.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.