A Special Public Avalanche Warning (SPAW) is in effect for this region. Natural avalanche activity will taper off somewhat on Saturday, but THE POTENTIAL FOR HUMAN TRIGGERED AVALANCHES REMAINS LIKELY.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
FRIDAY NIGHT - Cloudy with flurries, 5-10 cm / southwest winds , 25-65 km/h / alpine low temperature near -11SATURDAY - Cloudy with sunny periods and isolated flurries / south to southwest winds, 15-30 km/h / freezing level 800m / alpine high temperature near -8SUNDAY - Cloudy with sunny periods and isolated flurries, up to 5 cm / south to southwest winds, 20-40 km/h / freezing level 1400m / alpine high temperature near -2, low temperature near -8MONDAY - Mainly cloudy with flurries, 10-15 cm / south to southwest winds, 20-60 km/h / freezing level 1500m / alpine high temperature near -3, low temperature near -7
Avalanche Summary
Avalanche activity continues in the South Columbia region with numerous natural, human and explosives triggered avalanches to size 2.5 reported in the region on Thursday and Friday. Several of the human triggered avalanches were triggered from a distance (remote triggered).In the neighboring Glacier National Park region, artillery control produced size 2-3.5 avalanches on Thursday and Friday, some that terminated near the bottom of their run out zones. Reports suggest that some of the larger avalanches may have stepped down to the weak layer buried in mid November. A recent natural avalanche cycle to size 4 was reported in the neighboring Purcell region.
Snowpack Summary
60-90 cm of recent storm snow sits on a weak layer of facets (sugary snow), surface hoar (feathery crystals) and a sun crust (on south aspects). Strong winds have promoted widespread slab formation.Another weak layer of surface hoar and sun crust that formed in mid November is up to 120 cm below the surface. This layer is most likely to be a problem in areas where the surface hoar sits on the sun crust. This combination is most likely found on steep, south facing slopes at treeline. The potential may exist for smaller avalanches to step down and trigger this deeper layer, resulting in large avalanches.At the base of the snowpack is a crust that formed near the end of October. Concern for this layer is dwindling but it may still be worth considering in places such as steep, rocky, alpine terrain, especially where the snowpack is shallow. It would likely take a large trigger such as a cornice fall to produce an avalanche on this layer.
Problems
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.