Avalanche Forecast
Purcells
Avalanche danger will increase as snowfall and strong winds combine to form new winds slabs. Forecast amounts are uncertain, but whether thin or thick, new slabs are likely to be touchy. Watch for the impact of sun exposure in the afternoon.
Avalanche Problem 1: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be especially careful around wind loaded pockets near ridge crests and roll-overs.
- Minimize your exposure to any sun exposed slopes.
Avalanche Problem 2: Cornices
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Large cornice failures have been reported in the past week. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.
Travel and Terrain Advice
- Give cornices a wide berth when travelling on or below ridges.
- Cornices become weak with daytime heating. Always take stock of overhead hazards.
Avalanche Summary
Another round of explosives control in the north of the region on Thursday yielded several cornice and loose dry releases, as well as one more concerning size 3 persistent slab release that featured an 80-200+ cm crown fracture. This occurred on a north aspect at 2450 m. Numerous natural loose wet releases (to size 2.5) and several other recent natural storm slabs (to size 3) were also observed.
Reports from from Wednesday included an observation of a natural size 3 slab release that is believed to have released over a persistent weak layer, potentially from mid-March. Evidence of the release was seen from a distance in the Dogtooth range. Elsewhere in the north of the region, explosives control yielded several wind slabs, storm slab, and cornice releases, generally to size 2, with a couple of size 2.5. One size 3 deep persistent slab was also reported.
Reports from Tuesday included several observations of large (size 2) natural storm slab releases focused around steep features below ridgetop.
Looking forward, another round of snowfall is expected to introduce new surface instabilities over Friday night and Saturday.
Snowpack Summary
New snow is forecast to accumulate above a new melt freeze crust that can now be found on the surface on all but north aspects above about 2300 metres. Below it 30-40 cm of mostly settled storm snow overlies a crust on all aspects to at least 2000 m (and possibly higher on south-facing slopes), with up to 80 cm observed in some areas in the northwest of the region.
Within this storm snow there are several buried crusts with the mostly recently buried (down about 20 cm) now a limited concern with recent warm temperatures promoting settlement and bonding in the upper snowpack.
With warm daytime temperatures and poor overnight recovery of cold temperatures, there remains some lingering concern around the mid-March persistent weak layer in the alpine where it is found 60 to 100 cm below the surface. This buried crust/surface hoar interface is likely trending towards dormancy, but should be kept in the back of our minds for its capability to produce large avalanches should it be triggered with a heavy load, such as a cornice collapse.
Deeper persistent weak layers from December and January are considered dormant at this time.
Weather Forecast
Friday night: Light flurries bringing a trace to 5 cm of new snow. Moderate to strong southwest winds.
Saturday: Mainly cloudy with continuing flurries bringing 5-15 cm of new snow. Moderate to strong west winds. Freezing level to 1800 metres with alpine high temperatures around -4.
Sunday: A mix of sun and cloud. Light west winds. Freezing level to 1800 metres with alpine high temperatures around -3.
Monday: Mainly sunny. Light east winds. Freezing level rising to 2300 metres with alpine high temperatures around 0 to +2.
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New snow and increasing winds will begin to build new wind slabs in the lee of exposed terrain over Friday night and Saturday. Sun exposure may create very touchy conditions in the new snow later on in the day.