Avalanche Forecast
Purcells
The first sustained warmup of spring is finally here. Surface instabilities and cornice hazards should be firmly on your radar as you travel. Expect stability to deteriorate over the day.
Avalanche Problem 1: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
- Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.
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
- Give cornices a wide berth when travelling on or below ridges.
- Cornices become weak with daytime heating. Always take stock of overhead hazards.
Avalanche Problem 3: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
New snow and strong southwest winds have formed wind slabs in the lee of exposed terrain. Slabs may remain reactive to human triggering over the near term and reactivity may increase with daytime warming on Monday.
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 Summary
Decreasing traffic in the mountains have limited avalanche observations over the past few days.
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 noted.
A natural size 3 slab release was observed on Wednesday and is believed to have released over a persistent weak layer 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. 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, a period of increasing warming, full sun, and warm overnight temperatures will be maintaining elevated chances of cornice and loose wet avalanche activity.
Snowpack Summary
About 5-20 cm of new snow has been blown into wind slabs by strong southwest winds. The wind affected snow overlies 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
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. Weak overnight cooling.
Wednesday: Sunny. Light northwest winds. Freezing level to 3500 metres with alpine high temperatures around +8. Weak overnight cooling.
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Daytime warming and sun exposure will promote natural loose wet avalanche activity on Monday - especially around steep, sun-exposed terrain.