Avalanche Forecast
Purcells
Wind slabs of varying depth and reactivity exist in high elevation terrain and are likely to become increasingly reactive with daytime warming. Increase your caution around sun-exposed slopes as well as wind loaded areas.
Avalanche Problem 1: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Minimize your exposure to any sun exposed slopes.
- Be especially careful around wind loaded pockets near ridge crests and roll-overs.
Avalanche Problem 2: Cornices
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Large cornice failures have been reported in the past week and cornices will weaken with daytime warming. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.
Travel and Terrain Advice
- Cornices become weak with daytime heating. Always take stock of overhead hazards.
- Give cornices a wide berth when travelling on or below ridges.
Avalanche Problem 3: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Daytime warming and sun exposure will promote natural loose wet avalanche activity on Sunday - especially around steep sun-exposed terrain.
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, sunshine and warming temperatures are expected to promote natural and human triggered avalanches limited to new snow. The same warming may also cause natural cornice collapses.
Snowpack Summary
A trace to about 15 cm of new snow has accumulated above a melt freeze crust found on the previous surface on all but north aspects above about 2300 metres. Below it, 30-40 cm of mostly settled storm snow overlies a crust that shares similar distribution to the upper crust, 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
Sunday: A mix of sun and cloud. Light northwest winds. Freezing level to 1800 metres with alpine high temperatures around -5.
Monday: Sunny. Light south winds. Freezing level to 2400 metres and rising overnight. Alpine high temperatures around +2.
Tuesday: Mainly sunny. Light south winds. Freezing level to 3200 metres with alpine high temperatures around +5.
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New snow and strong winds will have formed new wind slabs in the lee of exposed terrain. Slabs are likely to remain reactive over the near term and reactivity is likely to increase with daytime warming on Sunday.