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Avalanche Forecast

Archived

Mar 12th, 2021–Mar 13th, 2021

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

Regions

Yukon.

East/Northeast wind Friday night into Saturday is expected to form another round of fresh wind slabs which will come to rest on a buried sun crust, these slabs may run faster & further than you'd normally expect. This adds to the damage done by southwest wind Thursday & Friday.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Cool and crisp, Sunday looks like a beautiful late winter day.

FRIDAY NIGHT: Overnight low around -21C, light to moderate northeast wind, trace of snow possible.

SATURDAY: Broken cloud cover, daytime high around - 14 C, strong east/northeast wind, 1 to 3 cm of snow possible.

SUNDAY: Clear skies, daytime high around -13 C, light variable wind, no snow expected.

MONDAY: Scattered cloud cover, daytime high around -5 C, strong south/southwest wind, no snow expected.

Avalanche Summary

Fresh wind slab avalanches were quite sensitive to triggering as observed in this MIN report from Thursday. Wind slabs also released naturally on Thursday.

Last weekend our field team was in the Wheaton. They observed avalanches to size 2.5 on south facing slopes, starting high on ridges and rolling well into and through the trees. See a couple of MIN posts here and here.

The term 'Wheatonesque whumpfs' is worth holding onto. Remember that a whumpf is an avalanche that tried, with one key ingredient missing -- slope angle. Whumpf the right terrain and you've converted it into the real thing, hopefully it's not rolling down ontop of you.

Snowpack Summary

Almost 20 cm fell Thursday into Friday which adds to the 10 to 15 that fell earlier this week. You can stay up to date with snowfall with the Fraser Camp Wx Station which is back up and running. All the new snow has been subject to strong southwest wind which has formed wind slabs that were quite touchy on Thursday. The wind is expected to switch to the east/northeast Friday night into Saturday which will add further insult to injury to our powder riding dreams.  

The Wheaton's continental snowpack is the kind of thing you'd find around Jasper or Kananaskis Country in the Rockies. It's a weak snowpack dominated by sugary facets and depth hoar, the icing is either layers or a fat cap of harder cohesive slab. It's an untrustworthy structure that requires really good terrain selection and travel habits, or a healthy dose of luck.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Recent new snow may be hiding windslabs that were easily visible before the snow fell.

Problems

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.