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Avalanche Forecast

Archived

Mar 19th, 2023–Mar 20th, 2023

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland, Kispiox, Microwave-Sinclair, Ningunsaw, Ningunsaw, South Bulkley, South Bulkley, Telkwa.

A layer of buried surface hoar is increasing reactivity and propagation in wind loaded features.

Watch for signs of instability increasing with daytime heating. Back off slopes as the surface becomes wet or moist from solar input.

Confidence

Moderate

Avalanche Summary

On Saturday, a few natural wind slab avalanches were observed up to size 2 in the alpine. Numerous loose wet avalanches to size 2 were observed in steep, rocky solar terrain and on all aspects below treeline.

On Friday, a size 3, 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.

Snowpack Summary

Southwest winds have built wind slabs on north to east facing terrain features near ridge top. A melt freeze crust or moist snow exists on the surface at low elevations and on sun affected slopes.

A weak layer of surface hoar is found 10-25 cm down in sheltered terrain. On solar aspects, this layer appears as a melt-freeze crust.

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.

Weather Summary

Sunday Night

Partly cloudy. Strong southeast winds at ridgetop. Treeline temperature -1°C. Freezing levels remain around 1300 m through the night.

Monday

Mainly sunny. Strong southeast winds at ridgetop. Treeline temperature 0°C. Freezing levels 1500 m.

Tuesday

Mix of sun and cloud. Moderate southwest winds at ridgetop. Treeline temperature 0°C. Freezing levels 1500 m.

Wednesday

Mix of sun and cloud with isolated flurries, 1-2 cm accumulation. Moderate west winds at ridgetop. Treeline temperature -4°C. Freezing levels 1000 m.

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.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.