Avalanche Forecast
Issued: Mar 18th, 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
A layer of buried surface hoar is increasing reactivity and propagation in wind loaded features.
Watch for changing conditions as you move through aspect and elevation bands.
Summary
Confidence
Moderate
Avalanche Summary
Slab avalanches have been reported over the week, naturally and rider triggered.
Of note: a size 3 (very large) naturally triggered deep persistent slab avalanche was reported in the Stikine area, on a south facing slope at 1300 m. This avalanche occurred on the basal facets, up to 250 cm deep, likely triggered by a combination of warm temperatures and sun effect. This is the only recent avalanche on this layer. Triggering is considered most likely during periods of rapid change to the snowpack. Several recent cornices failures were also noted throughout this region, entraining snow on the slopes below but not triggering a slab avalanche. In the right terrain cornice falls may be large enough to produce an avalanche on the deep persistent weak layer.
Wind slabs, around 25 cm deep have occurred primarily at higher elevations on north facing terrain features to size 2, including a remotely triggered size 1 Loose wet avalanche activity was noted on sun affected and low elevation terrain to size 1.
Snowpack Summary
Southwest winds have created reactive deposits on north to east facing terrain features near ridges. A melt freeze crust or moist snow exists on the surface at low elevations and on sun affected slopes into the alpine.
10-25 cm overlies large surface hoar crystals in terrain sheltered from the wind and sun, wind-affected snow in wind exposed terrain, and a hard melt-freeze crust on sun-affected slopes.
The middle of the snowpack is strong and contains numerous hard crusts.
The lower snowpack is composed of weak basal facets. This layer has produced limited recent avalanche activity, however it can quickly become active again with any significant change to the snowpack, such as rapid loading (heavy snowfall or rain) or prolonged and extensive warming. Avoiding thin and rocky slopes is still recommended. Cornices are also very large and a cornice failure could trigger this basal layer.
Weather Summary
Saturday Night
Mix of clear skies and cloud. Freezing levels 1500-1000 m.
Sunday
Mostly cloudy with up to 2 cm of snow. Strong southeast winds. Freezing levels rise to 1500 m. Alpine temperatures around -4 °C.
Monday
Cloudy skies and moderate to strong southeasterly winds. Freezing levels rise to 1500 m. Alpine temperatures around -4 °C.
Tuesday
Mostly cloudy. Freezing levels rise to 1500 m. Alpine temperatures around -4 °C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
Problems
Wind Slabs
Storm snow has been redistributed by southwest winds into deeper deposits, primarily found on north and east facing terrain features.
A buried layer of surface hoar is increasing reactivity and propagation. Avoid sheltered and shaded slopes where surface hoar is more likely to be found. On other aspects this layer is present as a melt freeze crust which has also produced avalanche activity.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
Weak, sugary faceted grains exist near the base of the snowpack. Riders are most likely to trigger this layer on steep, rocky slopes where the snowpack is shallow. The likelihood of avalanche activity on this layer will increase during periods of rapid change to the snowpack, such as heavy snowfall, rain, or rapid warming. Cornices are also very large at this time of year and a cornice failure could trigger this layer.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 19th, 2023 4:00PM
