North Columbia Avalanche Forecast

Mar 22nd, 2020 4:00PM

The alpine rating is moderate, the treeline rating is low, and the below treeline rating is low. Known problems include Wind Slabs.

New snow drifted by wind may form reactive slabs at upper elevations. Anticipate changing conditions and monitor the depth, cohesiveness, and bond of the new snow to the old snow surface.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Sunday night: Cloudy, 5-10 cm of snow, light southwest wind gusting moderate at ridge-tops, alpine temperature -6 C, freezing level 500 m. 

Monday: Cloudy, 5-10 cm of snow, light southwest wind, alpine temperature -8 C, freezing level 1400 m.

Tuesday: Mostly cloudy, 5-10 cm of snow, light southwest wind, alpine temperature -9 C, freezing level 800 m. 

Wednesday: Mix of sun and cloud, light west wind, alpine temperature -12 C, freezing level 

Avalanche Summary

Over the past several days, avalanche activity was reported as natural loose dry or loose wet avalanches size 1-2 running in steep, sun-exposed terrain. One large (size 2) slab avalanche released naturally as a result of strong solar radiation on a south aspect at 2500 m. There were also several large cornice failures on northerly aspects (up to size 2.5).

If you decide to travel in the backcountry, consider sharing your observations via the Mountain Information Network (MIN) to supplement our data stream as operators are shutting down. A conservative mindset and margins are recommended at this time.

Snowpack Summary

5-15 cm of new snow is forecast to accumulate by Monday afternoon. Moderate southwest winds at ridge-tops may build wind slabs primed for human triggering on lee features.

The new snow is falling on a variety of snow surfaces, consisting of sun crusts, hard wind-affected snow, and soft faceted snow. There have also been reports of surface hoar forming on sheltered, shady slopes. See this MIN for a helpful illustration from nearby Glacier National Park. It will be important to track the depth, cohesiveness, and bond of the new snow to these various old snow surfaces across aspects and elevations where you're travelling.

Cornices are large and looming. Two layers of buried surface hoar may be found buried 20-40 cm deep (March 10) and 60-120 cm deep (February 22). Though there is a low likelihood of triggering an avalanche on these layers, the consequences of doing so would be high. Avalanche activity on the Feb 22 layer was last reported on March 8th.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Make observations and assess conditions continually as you travel.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible-Likely

Expected Size

1 - 2

Up to 15 cm of new snow may accumulate by Monday afternoon in favored areas. Wind slab avalanches may increase in their sensitivity to human-triggering where moderate southwest winds are loading the new snow into slabs on lee features.

Aspects:

North, North East, East, South East, South, West, North West.

Elevations:

Alpine, Treeline.

Valid until: Mar 23rd, 2020 5:00PM