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Avalanche Forecast

Archived

Feb 3rd, 2020–Feb 5th, 2020

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

North Rockies.

Windy weather, with more snow expected, is keeping avalanche hazard elevated at treeline and alpine elevations. Minimize exposure to overhead wind-loaded slopes and cornices. The best riding is near treeline elevations in areas protected from the wind.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday and Monday were the clearing between storms; the next storm expected to arrive Tuesday

Monday Overnight: Mix clouds and clear periods with temperatures in the minus teens. No new precipitation. Moderate west to southwest winds.

Tuesday: WINDY. Cloudy with very strong southwest or west winds . Snow with accumulations around 10 to 30 cm. Temperatures around -5 to -10 C.

Wednesday: Continued strong southwest or west winds. Continued snow with another 5 to 20 cm accumulating. Temperatures warming to near zero at 1500m.

Thursday: Cooling back to below zero temperatures with a northwest moderate wind. Dry with a mix of sun and clouds.

Avalanche Summary

Storm slab and wind slab avalanches reported from steeper slopes and slopes lee to southwest winds were reactive during and after the weekend storm. There's still snow avaiable to transport, as well as ongoing winds, so I expect wind slab activity may be ongoing. 

Snowpack Summary

The Feb 01 weekend storm was warm and wet. Below a certain elevation, somewhere around 15 - 1700 m, the precipitation fell as a soaking rain which is now a frozen crust and avalanche concerns are minimal. Above this elevation there was 50 cm or more of recent snow, and strong winds creating both wind slab and cornice concerns. 

In the mid-pack there may still be a layer of surface hoar buried in late December. It's gaining strength, but may remain a concern. The warm wet storm on Feb 01 will have tested this layer in the short-term and will improve it in the longer-term; however, we're awaiting evidence before considering it dormant. This layer is found across much of the North Rockies region but our focus is around McBride and the McGregors/Torpy.

Terrain and Travel

  • Dial back your terrain choices if you are seeing more than 30 cm of new snow.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.

Problems

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.

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.