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Avalanche Forecast

Archived

Apr 22nd, 2018–Apr 23rd, 2018

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

Regions

Northwest Coastal.

Avalanche danger will increase as the temperatures rise throughout the week.

Confidence

Low - Due to the number of field observations

Weather Forecast

MONDAY: Mostly cloudy. Strong southwest wind. Alpine temperature +5. Freezing level 1600 m.TUESDAY: Mix of sun and cloud. Moderate west wind. Alpine temperature +3. Freezing level 1400 m. WEDNESDAY: Sunny. Light west wind. Alpine temperature +10. Freezing level 3000 m.

Avalanche Summary

Several very large deep persistent slab avalanches(size 3-4) which were triggered by cornice failures and several natural wind slabs up to size 2.5 were reported near Bear Pass on Saturday. Avalanche reports have been limited due to very few information sources this time of year. If you have been out, please post your observations on the Mountain Information Network. (MIN)

Snowpack Summary

Cornices are large and when they fail there is the potential to trigger large avalanches on deeply buried weak layers. Lingering wind slabs may still be reactive to human triggers on leeward slopes below ridgetops.In the south of the region, two layers of surface hoar are buried early-March and mid-March are approximately 70-100 cm deep and most prominent on north to east aspects. Further north, these layers are around 40 cm deep.Below these March layers the mid-pack is generally well-settled and strong. However in the far north of the region there are weak sugary facets near the bottom of the snowpack.

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.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.