Bulletin d’avalanche

Lizard-Flathead

Feb 26 – 27, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Sun
Mon
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

Travel in avalanche terrain is not recommended on Friday. Natural avalanche activity may start to taper later in the day, however; slopes remain primed for skier and rider triggering. 

A Special Avalanche Warming is in effect for this region. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    2–3

    Many large avalanches have been triggered on this layer of surface hoar, faceted grains, and/or a melt-freeze crust, found around 70 to 100 cm deep. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine. Avalanches have occurred on surprisingly shallow slope angles and the layer can easily be remotely triggered.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–2

    30 cm of new snow fell Thursday. Storm and wind slab avalanches are reactive. The natural avalanche activity may taper off on Friday but these slabs will remain primed for skier and rider triggering. The slabs may be around 20 to 50 cm thick, depending on how much snow fell in your riding area, and they may overly sugar faceted grains. 

    Loose-dry avalanches may be easily triggered, especially if the sun pokes out. 

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Thursday NIght: 10-15 cm of snow accompanied by moderate to strong southwest wind. 

Friday: Cloudy with some sunny periods, snow amounts 5-10 cm with possible enhancements. Ridgetop wind moderate from the West and alpine temperatures near -5. Freezing levels 1000 m.

Saturday: A mix of sun and cloud with possible flurries. Ridgetop wind strong from West and alpine temperatures near -10. Freezing level at valley bottom.

Sunday: Cloudy with isolated flurries. Ridgetop wind moderate from the southwest and alpine temperatures near -3. Freezing level 1100-1500 m.

Avalanche Summary

 

On Thursday, numerous skier-controlled and natural slab avalanches were reported up to size 2. Loose-dry avalanches were reported up to size 1.5 and running fast and far. 

On Wednesday in the South Rockies region, this MIN report highlights a critical incident of a rider-triggered persistent slab size 3. Also on Wednesday, this MIN report indicates another remotely-triggered size 2 slab avalanche. Whether it's a wind slab or a persistent slab problem, they're catching folks by surprise and will not heal quickly.

Many large (size 2 to 3) slab avalanches were triggered naturally, by skiers, and using explosives on Monday through Wednesday. The slabs were generally 30 to 70 cm thick, most often at treeline and alpine elevations, and occurred on all aspects but many of them on north to east aspects. 

Looking towards Friday, human triggering of storm, wind, and persistent slabs will remain likely. Conditions are not easily managed right now, warranting a conservative mindset!

Snowpack Summary

Stormy conditions enter the region on Thursday, bringing new snow up to 30 cm and strong wind. Reactive storm slabs exist in sheltered areas at all elevations and on all aspects. Wind slabs are expected to build over the day in exposed terrain at treeline and alpine elevations in lee terrain features. These slabs will build on top of storm slabs formed early this week that still may be triggerable by riders, particularly where they overly sugary faceted snow from mid-February's cold drought.

A persistent weak layer found around 50 to 80 cm deep that was buried late-January has been prevalent in the region during February. The layer may consist of weak and feathery surface hoar, sugary faceted grains, or faceted grains associated with a hard melt-freeze crust. Persistent slab avalanches remain reactive and continue to surprise skiers and riders almost daily. Avoidance of consequential slopes is the best way to ensure a safe day right now.

There are presently no deeper concerns.

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Make conservative terrain choices and avoid overhead hazard.

Régions couvertes