Avalanche Forecast
Issued: Mar 7th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
MBender,
Avalanche Canada
Wind slabs at upper elevations are the main concern. Buried weak layers in the northern tip of the region may still be reactive.
Summary
Confidence
High - The snowpack structure is generally well understood.
Weather Forecast
SUNDAY Night: Cloudy with isolated flurries, accumulation 1-5 cm. Light to moderate west wind. Alpine high temperatures around -9 C. Freezing level at valley bottom.
MONDAY: Mix of sun and cloud. Light and variable winds. Alpine high temperature -6. Freezing level 1400 m.
TUESDAY: A mix of sun and cloud. Light variable winds shifting west. Alpine high temperature -5. Freezing level 1500 m.
WEDNESDAY: Cloudy with isolated flurries. Light to moderate northwest wind. Alpine high temperature -4. Freezing level 1500 m.
Avalanche Summary
While in most parts of the Purcells the main concern is wind slabs, backcountry travelers in the northern tip of the region should be extra cautious about a lingering persistent slab problem.
Warm sunny weather between Wednesday and Friday resulted in a widespread cycle of wet loose avalanches on sun-exposed slopes. Cooling temperatures have since worked to stabilize this problem.
Last week there were several notable reports of large human triggered persistent slab avalanches in the Dogtooth Range and Quartz Creek area. See these MIN reports here and here.
Snowpack Summary
5-15 cm of new snow over Friday night accumulated above moist and crusty interfaces that formed during the recent warm up. Some deeper accumulations can be expected in lee terrain features. High shaded terrain will have a mix of soft snow and some old buried wind slabs.Â
Persistent weak layers have been most active in the northern end of the Purcells where a buried layer of surface hoar that formed in late January is 40-80 cm deep and an older surface hoar layer is 60-120 cm deep at treeline. These layers may exist as a combination of facets and crusts at other elevations. Recent observations suggest these layers have been less problematic as you move further south.
Steep rocky areas where the snowpack is thin likely have additional weak layers near the base of the snowpack.
Terrain and Travel
- If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
- Be carefull around freshly wind loaded features.
- Caution around convexities or sharp changes in terrain.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Problems
Wind Slabs
Primarily southwest winds have created new wind slabs on north and east aspects. Older, buried slabs may exist on all aspects in steep high elevation terrain.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Persistent slab avalanches remain possible in the northern tip of the Purcells where there has been recent avalanche activity on a 40-80 cm deep layer of surface hoar, facets, and/or crusts (see Avalanche Summary).
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 8th, 2021 4:00PM
