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Avalanche Forecast

Archived

Jan 31st, 2020–Feb 3rd, 2020

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

Regions

North Rockies.

WIth the forecast storm avalanche hazard will rapidly rise to HIGH on Saturday. A widespread natural avalanche cycle is expected at all elevations.

Confidence

High - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather.

Weather Forecast

Friday Overnight: Warm, wet, intense storm ramping up. Freezing level rising to 2000m. Strong southwest wind. Precipitation of 15 to 30 mm water equivalency. Normally that means 20 to 60 cm of snow; with this storm it means soaking rain at lower elevations and up to 30 cm of snow at the highest elevations.

Saturday: Freezing levels lowering with temperatures falling back below freezing by end of day. 5 to 15 mm of water equivalent translates into, depending on your elevation: rain, a mix of rain & snow, or up to 15 cm of snow. Strong west winds.

Sunday: Mix of sun and cloud. Flurries for most of the region but up to 10 cm of snow in western upslope locations. Temperatures have cooled down to around -10 C in the mountains with moderate northwest winds

Monday: Dry. Mix of sun and cloud. Temperatures steady around -1- to -15 C. West to northwest wind at moderate strength.

Avalanche Summary

WIndslabs continue to be reported throughout the region, with this MIN report (with great photo) being a good example of the type of problem we're dealing with. Recent ones were in the size 1 to 1.5 range.

Looking forward, a warm wet storm will create a Loose Wet avalanches at lower elevations and increase the likelihood of Storm Slabs (and Wind Slabs) at higher elevations.

Snowpack Summary

Here's a snowpack description as of Friday Jan 31 before the forecast warm wet "atmospheric river" (previously know as a pineapple express) storm arrives. This description will obviously no longer apply once hit by soaking rain at lower elevations .... The upper snowpack is right-side-up meaning light dry & fluffy (aka powder) at the surface which gradually blends into increasingly harder and stronger snow with depth.The weeks-long weather pattern of snow & wind also means there are widespread storm and wind slabs.

In the mid-pack there's a layer of weaker surface hoar buried in late December that remains a concern but is gaining strength. This layer is found across much of the North Rockies region but our focus is around McBride and the McGregors/Torpy. It's a classic surface hoar layer that's most prominent in sheltered treeline features 50 to 150 cm below the surface.

Terrain and Travel

  • Watch for rapidly changing conditions during periods of heavy loading from new snow, wind, or rain.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Loose avalanches may start small but they can grow and push you into dangerous terrain.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.