Avalanche Forecast
North Columbia
Avalanche danger will increase on sunny slopes where wet loose avalanches are very likely. Concern is increasing for persistent slabs and cornices.
See the Forecaster's Blog for more: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up
Avalanche Problem 1: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid exposure to sunny slopes, especially in the afternoon.
- Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Rising temperatures and strong sunshine are increasing concern for weak layers buried deep in the snowpack. In addition to human triggering in thin spots, solar warming and cornice releases are possible natural triggers for persistent slabs.
Travel and Terrain Advice
- Avoid convoluted terrain with variable snow depths and multiple trigger points.
- Pay attention to overhead hazards like cornices which could trigger persistent slabs.
- Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.
Avalanche Summary
A widespread natural avalanche cycle to size 3.5 was reported throughout the weekend and Monday. These avalanches were primarily wet loose avalanches on sunny aspects; however, some did step down to the mid-February layer (with 50-70 cm crowns) on southerly aspects.
Reports from Friday included observations of numerous storm slabs and wind slabs that ran from size 1.5 to 2.5. These were triggered naturally as well as with ski cutting and all aspects and elevations were represented.
Avalanche activity is expected to increase as we move into a period of intense sun and prolonged warming. Predictable loose wet avalanches from steep, sunny terrain should be easy to manage. A trickier problem will emerge as warmth penetrates into the snowpack to tickle deeper persistent weak layers. This will be a time to avoid exposure to large sunny features and keep well away from corniced slopes.
Snowpack Summary
15-25 cm of snow from Thursday into Friday sits on sun crusts on solar aspects and well-settled storm snow on more northerly aspects. Several other sun crust layers may be found within the older storm snow on solar aspects. The main story, however, has been the sun's effect on south and west facing slopes over the past three days. Daytime heating has resulted in moist or wet snow on sunny aspects, freezing to form a crust overnight.
A couple of layers buried in mid to late February (down around 50-100 cm) are variably reactive, and have the potential to create surprisingly large avalanches if triggered. Initially, these interfaces were most reactive on solar aspects, where they present as buried sun crusts. However, persistent slabs have been triggered on shady aspects too, where surface hoar and/or facets exist.
Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with forecast warming, a surface avalanche stepping down, cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets.
Weather Forecast
Sunny and warm until light precipitation arrives on Wednesday.
TUESDAY: Mainly sunny with some thin cloud. Light to moderate southeast winds. Freezing level to 2500 metres with alpine high temperatures of +3.
WEDNESDAY: Cloudy with rain changing to flurries in the afternoon (2-5 cm possible). Light to moderate south west winds. Freezing level falling to 1700 metres late in the day, with alpine high temperatures of +1.
THURSDAY: Scattered flurries (2-5cm). Light southerly winds. Freezing level around 1500 metres with alpine high temperatures around 0 degrees.
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Wet loose avalanches are very likely in steep, rocky, sunny terrain. Warming could also wake up more deeply buried weak layers, creating a surprisingly large avalanche.