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Avalanche Forecast

Archived

Feb 29th, 2020–Mar 1st, 2020

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

Regions

Cariboos.

Limit exposure to large avalanches by sticking to simple terrain. A buried Surface Hoar layer lurks and is showing signs of touchy human triggered avalanches with recent snow, especially where snow is wind affected. Check out this Fx blog on Surface Hoar.  

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

SATURDAY NIGHT: Cloudy with clear periods. Winds light to moderate North. Alpine low temperature -15 C with freezing levels at valley bottom.

SUNDAY: A mix of sun and cloud with scattered flurries, accumulations Trace to 5cm. Winds moderate Southwest. Alpine high temperatures near -9 C and freezing levels 600m.

MONDAY: Mainly cloudy with sunny periods and isolated flurries, accumulations Trace to 10cm. Winds moderate West gusting strong. Alpine temperatures high of -6 and lows -10 C with freezing levels near 1200m.

Tuesday: Mainly cloudy with snow flurries, accumulation 5-15cm. Winds moderate to strong West gusting extreme. Alpine temperatures high of -6 and lows -10 C with freezing levels near 1200m

Avalanche Summary

Early reports from Saturday include numerous easily triggered large (size 2) human triggered avalanche on Surface Hoar down 50-70cm at treeline.  

On Friday there were numerous reports of small (Size 1) skier triggered avalanches on Surface Hoar down 40-50cm from 1400-2100m on all aspects.  

Check out this MIN for a report of how the high freezing levels on Friday impacted low and mid elevation  

Snowpack Summary

10-25cm of snow fell across the region Friday into Saturday with more snow reported in the North and adjacent to highest of mountains. Winds were moderate to strong from the Southwest as new snow fell. This new snow likely formed widespread wind affect and wind slab in Alpine and exposed treeline locations, particularly near ridges.  

40-70 cm or recent snow now overlays the widespread Surface Hoar (size 5 to 15 mm) that was found at all elevations and on all aspects. Recent warm temperatures have built slab like properties in this recent snow, particularly at mid and low elevations.

There is variability in the reactivity and distribution of this layer, particularly in the northern half of the region. In the southern half, this layer exists on all aspects and elevations except for steep, sun-exposed aspects where it was melted by sun and formed a melt-freeze crust. So far, the overlying snow has been reactive to human activity where the wind has redistributed it, forming a slab. This has been most common around treeline and alpine elevations in the south of the region.

The mid and lower snowpack is generally well-settled and strong.

Terrain and Travel

  • Stick to simple terrain or small features with limited consequence.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.