Avalanche Forecast
Purcells
Sustained and shifting winds are expected to quickly redistribute light new snow amounts into reactive new wind slabs. Seek out sheltered lower elevations on Friday.
Avalanche Problem 1: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Give cornices a wide berth when travelling on or below ridges.
- Watch for new slabs on a wide range of aspects due to a shift in wind direction.
- Use extra caution around sheltered north aspects where slabs may overlie surface hoar.
Avalanche Summary
Wednesday's reports included observations of several recent natural storm slab releases from Size 1-2, seen on steep alpine slopes on a range of aspects. One small (size 1) ski cut storm slab that released over a sun crust was also reported, as well as natural and ski cut loose dry releases from size 1-2.
Reports from the weekend and earlier in the week included observations of recent loose dry releases that reached size 2 as well as several natural as well as skier and sled-triggered storm slabs from size 1-2. The slabs have been failing from 15-30 cm deep on a steeper north through east aspect in the alpine.
Explosive control work on Saturday produced several cornice failures up to size 2.5 that entrained loose snow on underlying slopes without triggering slabs.
Looking forward, avalanche danger will be increasing as strong southeast to southwest winds and light snowfall form new slabs over Thursday night. These newly formed slabs are likely to be touchy and reactive to human triggering over the near term. The convective nature of forecast snowfall suggests that localized pockets of enhanced precipitation may lead to increased avalanche danger in parts of the region.
Snowpack Summary
Recent light snowfalls (5-15 cm each) have been followed by warm daytime temperatures and glimpses of sun, setting up a couple of thin storm snow layers over temperature and sun crusts at lower elevations and on south aspects. On shaded aspects at higher elevations, Sunday's snowfall buried a layer of surface hoar now found 10-15 cm deep.
New snow amounts taper with elevation and below 1700 m, only minimal accumulations have buried a supportive crust on all aspects. This crust will likely break down with daytime warming, becoming moist in the afternoon.
Deeper persistent weak layers from mid-late February (down 40 -100 cm deep) as well as January and December layers are generally considered dormant, but could wake up with a surface avalanche stepping down, cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets. Facets also linger at the base of the snowpack.
Weather Forecast
Thursday night: Flurries bringing 5-10 cm of new snow. Moderate to strong southeast winds shifting to southwest.
Friday: A mix of sun and cloud with continuing isolated flurries and a trace to 5 cm of new snow. Moderate to strong southwest winds. Freezing level to 1100 metres with alpine high temperatures around - 9.
Saturday: A mix of sun and cloud with isolated flurries and a trace to 5 cm of new snow. Light southwest winds. Freezing level to 1100 metres with alpine high temperatures around -10.
Sunday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1000 metres with alpine high temperatures around -10.
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Forecast snowfall and strong winds are expected to form touchy new wind slabs on Friday. High elevation north aspects are a special concern for harbouring buried surface hoar that will be increasingly stressed by wind loading.