Avalanche Forecast
Issued: Feb 28th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
wlewis,
Avalanche Canada
Steer clear of freshly wind loaded features. Wind slabs are expected to remain reactive to human triggers.
Avoid thin and rocky start zones, especially in the alpine where deeply buried weak layers remain concerning.
Summary
Confidence
Moderate
Avalanche Summary
The storm produced avalanches up to size 3 from natural and rider triggers, and explosive control methods. Many avalanches have occurred within the storm snow or on the old snow surface, while some failed on the buried surface hoar layer.
Deep persistent slab avalanches continue to be periodically reported throughout the Purcells.
On Monday a naturally trigged size 2.5 avalanche stepped down to the basal facets on an east facing alpine slope.
This MIN post from Thursday observed a size 3 avalanche near Golden over 1 m deep.
Avalanche activity on this deeply buried weak layer is expected to continue as the snowpack structure remains weak and will be slow to gain strength. Similar activity may be occurring in the Rockies however we have less operators and observations coming from this area.
Snowpack Summary
Up to 20 cm of low density recent storm snow sits over wind affected surfaces. Expect deeper deposits on north and east facing slopes, from southwest winds.
Buried surface hoar sits 30-50 cm deep in sheltered terrain features, and a thin sun crust exists at the same depth on steep south-facing terrain.
The lower snowpack contains a number of buried weak layers such as surface hoar with variable distribution, as well as a widespread layer of large, weak basal facets and depth hoar in some areas. These weaknesses have been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.
Weather Summary
Tuesday Night
Mainly cloudy with isolated flurries. Light snowfall is expected in southern areas near Cranbrook. Light and variable winds. Freezing levels valley bottom.
Wednesday
Mix of sun and cloud. Light westerly wind. Alpine high of -8 °C. Freezing levels 500 m.
Thursday
A mix of sun and cloud with freezing levels rising to 1000 m. Alpine highs reach -3°C. Moderate to strong southwest winds. Light snowfall possible.
Friday
Mix of sun and cloud with moderate westerly winds. Freezing level around 500 m. Isolated flurries are possible.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Wind Slabs
Moderate winds and recent storm snow have built reactive slabs at higher elevations. Slabs may sit over a layer of surface hoar in sheltered terrain features, or over a sun crust on south facing slopes which may increase reactivity.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
The base of the snowpack remains very weak. Very large human triggered avalanches are possible at higher elevations. Avoid shallow and rocky areas, where the snowpack varies rapidly from thick to thin.
The mid and lower snowpack also contain several surface hoar layers, most prominent in the Purcells. Due to the overall weak snowpack structure, small avalanches are likely to step down to any of these deeper weak layers creating large and destructive avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 1st, 2023 4:00PM
