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Avalanche Forecast

Archived

Mar 17th, 2023–Mar 18th, 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, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

The March sun packs a punch and can quickly destabilize the snowpack. Be suspect of sunny slopes or overhead hazards like cornices during the heat of the day.

Confidence

Moderate

Avalanche Summary

On Thursday, loose wet avalanches to size 1.5 were observed in steep, solar terrain.

On Tuesday, a natural size 2 wind slab and size 3 glide slab were reported both around 1300 -1500 m. A skier-triggered storm slab was also reported on Zoa. The slab was a size 1.5 and was triggered near the top of the slope with no involvement. It was 40 cm deep and slid clean on the underlying old snow surface. Check out the MIN HERE. Thanks for the report and happy to hear everyone was ok.

A natural persistent slab size 3 was reported on Tuesday but it's suspected that it failed Monday during the storm. This avalanche happened on a shady aspect at 1800 m, with the failure plane unknown but suspect an early March interface.

Natural and human-triggered avalanche activity may occur through the weekend with rising freezing levels and solar radiation.

Snowpack Summary

Daytime warming and solar radiation will promote moist snow surfaces, destabilizing the upper snowpack on all aspects upwards of 1700 m and to ridgetop on solar slopes. Strong southwest winds may have formed reactive wind slabs at higher elevations and cornices loom over ridgelines.

The recent 40 cm of storm snow overlies a variety of old snow surfaces, including a sun crust on solar aspects, a melt-freeze crust at lower elevations and a spotty surface hoar in sheltered locations.  Reports indicate that the slab may poor bond to the underlying crust, especially around 1500 to 1800 m.

Additionally several crusts in the mid/lower snowpack. Their depth ranges from 150 to 250 cm. The mid and lower pack is generally settled and bonded in thicker snowpack areas, with a lingering concern for these deeper buried interfaces in shallower snowpack areas.

Weather Summary

Friday night

Scattered clouds and starry breaks. Treeline low temperatures -5. South wind 10-20 km/hr. Freezing level dropping to 1300 m, inversion developing.

Saturday

Mix of sun and cloud. South wind 10-20 km/hr. Treeline high temperature +3. Freezing level 1900 m.

Sunday

Increasing cloudiness. Southeast wind 10-30 km/hr. Treeline high temperature +2. Freezing level 1600 m.

Monday

Wet flurries, 5 mm. South wind 15-30 km/hr. Treeline high temperature +1. Freezing level 1200 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Wind slabs may be poorly bonded to the underlying crust.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

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.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.