Avalanche Forecast
Issued: Jan 18th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.
mconlan,
Avalanche Canada
Wind slabs may be touchy and a warming trend has the potential of waking up buried weak layers. Travel conservatively during this period of uncertainty.
Summary
Confidence
Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
SATURDAY NIGHT: Cloudy with isolated flurries, trace accumulation, moderate west wind, alpine temperature -10 C, freezing level below valley bottom.
SUNDAY: Mostly cloudy with isolated flurries, accumulation 1 to 3 cm, moderate to strong southwest wind, alpine temperature -5 C, freezing level rising to 800 m.
MONDAY: Mix of sun and cloud, moderate southwest wind, alpine temperature -3 C, freezing level 1000 m.
TUESDAY: Cloudy with snowfall, accumulation 5 cm, light southwest wind, alpine temperature -6 C, freezing level 700 m.
Avalanche Summary
On Thursday and Friday, wind slab avalanches were triggered naturally, by skiers, and explosives. They occurred on north and easterly lee terrain features, generally at and above treeline. They generally averaged 30 to 50 cm deep.
The last deep persistent slabs were reported last Monday and Tuesday. They were large (size 2-3) and were triggered naturally and with explosives in steep alpine terrain. The likelihood of triggering this layer may increase in the coming days as the air temperature rapidly rises.
It has been over one week since any persistent slab avalanches on the December surface hoar layer have been reported, although there could still be lingering concerns about triggering that layer on isolated slopes in steep treeline clearings.
Snowpack Summary
Strong southwest wind may produce fresh wind slabs in lee terrain features, particularly near ridges. Wind slabs have been reported as having the potential to propagate far.
A layer of surface hoar that formed in late December appears to be less reactive than it was a week ago and can be found 70 cm deep around Golden, 30 cm deep around Invermere, 70 cm deep around Kimberley, and 100 cm deep along Kootenay Lake. As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones. The likelihood of triggering buried weak layers may increase as the air temperature rises.
Terrain and Travel
- Avoid freshly wind loaded terrain features.
- Extra caution for areas experiencing rapidly warming temperatures for the first time.
- Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.
Problems
Wind Slabs
Strong southwest wind is forecast, along with a dusting of new snow and an increasing freezing level. Wind slabs may be touchy in lee terrain features, particularly near ridges.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A layer of surface hoar is buried 30 to 100 cm deep. There is uncertainty on whether the layer will reawaken during the air temperature rise. Use added caution during periods of warming, particularly in clearings around treeline.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Triggering large deep persistent slab avalanches is a low likelihood but high consequence problem that is most likely in shallow, rocky start zones. The likelihood of triggering deeper weak layers may increase as the air temperature rises on Sunday and Monday.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 19th, 2020 5:00PM
