Forecast precipitation is uncertain on Friday. Areas south of Nakusp may receive more snow than is currently forecast. If amounts are locally higher than indicated, danger may be Considerable.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
THURSDAY Night: Mainly cloudy with isolated flurries, light to moderate southeast wind, alpine temperature -9 C.FRIDAY: Flurries, accumulation 5-15 cm , light to moderate southwest wind, alpine temperature -8 CSATURDAY: Flurries, accumulation 5-15 cm, light west wind, alpine temperature -9 CSUNDAY: Mix of sun and cloud, light northeast wind, alpine temperature -13 C
Avalanche Summary
Numerous size 1-2 windslab, storm slab and persistent slab avalanches were reported from areas in the south of the region on Tuesday and Wednesday. These were predominantly at treeline and in the alpine on all aspects. In the the north part of the region avalanche activity on Wednesday was primarily reported as windslabs to size size 1.5 on north, west and south aspects in the alpine and at treeline.
Snowpack Summary
Up to 25 cm of new snow fell in the southern portion of the region (south of Nakusp) Tuesday into Wednesday. 5-10 cm fell further north. This new snow is sitting on previously wind-affected surfaces, sugary facets or feathery surface hoar. Beneath this lies two weak layers of surface hoar, which have produced large avalanches in the region. A layer that was buried at the end of January is around 30 cm deep and a layer buried mid-January is between 40 and 90 cm deep. The mid-January layer may also be associated with a melt-freeze crust on southerly aspects. These layers are most prominent at treeline and below.The remainder of the snowpack is generally well-settled. However, there have been sporadic reports of very large avalanches that have released near the base of the snowpack. Most of the avalanches have been in the high alpine. There has been about one report a week for the past month.
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.