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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, 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.

Regions

Coquihalla, Harrison-Fraser, Manning, Skagit.

Warm spring daytime temperatures are here - watch for surface snow turning wet and be wary of cornices and overhead hazards.

Confidence

Moderate

Avalanche Summary

On Friday and Saturday, loose wet avalanches to size 2.5 were observed on East to Southwest aspects. Glide slabs have been opening and running to size 2.5 in regular/common locations.

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.

Snowpack Summary

Daytime warming or wet flurries will promote moist snow surfaces, continuing to destabilize the upper snowpack. Cornices loom over ridgelines and may become weak during periods of solar radiation or warming.

A moist surface/sun crust has formed on all aspects up to 1800 m and solar aspects into the alpine. Last week's 40 cm of snow covered 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. The storm snow was most reactive on southerly slopes 1500-1800 m, sitting on an old sun crust.

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

Sunday night

Starry sky with increasing clouds. Southeast wind 10-20 km/hr. Treeline low temperature -4 C. Freezing level 1400 m.

Sunday

Unsettled and cloudy, light wet flurries during the day, 5 mm. Southeast wind 15-25 km/hr. Treeline high temperature +2 C. Freezing level 1600 m.

Tuesday

Light wet flurries transitioning to sunny breaks. Light northeast wind. Treeline high temperature +3 C. Freezing level 1500 m.

Wednesday

Sunny and calm. Light northerly wind. Treeline high temperature +2 C. Freezing level 1600 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
  • Wind slabs may be poorly bonded to the underlying crust.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Rain or periods of intense solar radiation can rapidly enhance the effects of warming.

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.

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.