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Avalanche Forecast

Archived

Mar 16th, 2023–Mar 17th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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. Avoid sunny slopes or overhead hazards like cornices during the heat of the day.Wind slabs may be primed for human triggering at upper elevations.

Confidence

Moderate

Avalanche Summary

No new reports on Wednesday.

On Tuesday, a natural size 2 wind slab and size 3 glide slab were reported both around 1300 m to 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 up to 1600 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

Thursday Night

Clear with some cloudy periods. Alpine temperatures near -2. Wind southeast 20 km/hr and freezing level valley bottom.

Friday

A mix of sun. Alpine temperatures near +4. Winds south 15-30 km/hr. Freezing level 1800 m.

Saturday

A mix of sun and cloud. Alpine temperatures near +5. Wind southeast 10-30 km/hr. Freezing level 1800 m.

Sunday

Cloudy. Winds 10-20 km/hr from the southeast. Alpine temperatures near +6 with freezing levels 2000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs may be poorly bonded to the underlying crust.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • 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

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.

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.