Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Tue
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The Elk Mountains are getting walloped by powerful storms and large avalanche cycles.  A brief lull in the storm track this morning - CONSIDERABLE danger- will give way to rising danger later today.  The danger will rise to HIGH above treeline sometime around sunset, and expand to all elevations overnight as snowfall intensifies.    Avalanche conditions are dangerous.  Windward and low-angle terrain offer the safest options.  The threat of long-running natural avalanches will increase throughout the day and overnight.   Choose conservative routes with minimal overhead hazards.  

 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2.5–3.5

    Large and destructive avalanches are sensitive to human triggers and will become increasingly susceptible to natural failures over the next 24 hours.  Dangerous avalanches are breaking several feet thick or more on weak layers in the bottom half,  and can run long distances.    Persistent slabs are most common on northerly and easterly aspects, where weak layers are more fragile and slabs are more widespread.  Given how thick these slabs are, you may not observe any obvious signs of instability. For example, two large avalanches were human triggered on Mt Emmons on Saturday; neither group reported any warning signs, such as collapses or shooting cracks.  

    A persistent slab triggered from a low angle ridgeline on Red Lady Glades. The slide broke 3 to 4 feet deep and ran far.

  • Storm Slabs

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

    Yesterday's extreme southwest winds left thick drifts behind leeward features.  Today's snowfall and increasing winds will form fresh slabs on a variety of aspects later today.  Instabilities in the upper snowpack could step down and trigger a very large avalanche.  Monitor for fresh slab development on windward aspects and avoid steep terrain on leeward aspects, where slabs are larger and are more likely to trigger a deeper instability.   

     

    An example of an avalanche earlier this season, that propagated widely below a wind-loaded ridgeline.  

Avalanche Discussion

This video gives a brief snowpack history and context as to why avalanche conditions are dangerous right now.   Yesterday's blizzard brought up to 1.4" of SWE (about 12" of snow) to the Northwest Mountains, and about half that  Southeast Mountains.  Extreme alpine winds blasted the mountains with sustained speeds at 60 mph and gusting to 120.  With whiteout conditions yesterday, our avalanche observations came to a halt, but at least one destructive slide crossed a mining road in the Northern San Juans.  Surely, similar activity was going on in our backyard, we just couldn't see it. The extreme winds reduced the distribution of problematic slabs on south to west aspects while likely beefing up the size of slabs on north to east aspects.  As if they aren't fat enough.    Steep, leeward terrain should be on your "ABSOLUTELY NOT" list.  Not on. Not underneath.  With careful snowpack evaluation, you can navigate the southwest quadrant of the compass with less risk.  These aspects have seen relatively fewer avalanches in the past few days because slabs aren't as widespread from wind erosion, and because buried crust layers are a bit stronger than their adjacent aspects.  

Snowfall ramps up through the day and surges with intensity shortly after sunset.  By tomorrow morning, we could see 30" in the Paradise Divide bullseye and around 12" to 20" elsewhere.  A natural cycle is poised to unleash another round of destructive avalanches, this time with more ammo in the gun.   The peak of instability looks to occur during the overnight hours, but weather models keep pushing the heavy snowfall closer to sunset, so we're showing HIGH danger above treeline today to account for some uncertainty with the timing.  The HIGH danger expands to all elevations after sunset.  We've issued an avalanche WATCH this morning and are expecting to upgrade to a WARNING later this afternoon.  Plan accordingly if your tour or travels are extending late into the day.  We don't recommend traveling below avalanche terrain as snowfall rates intensify this evening.  That includes common road routes such as Kebler Pass, Peanut Lake, or Gothic Road.  A fresh batch of storm and wind slabs will be developing on top of our ogre of a persistent slab problem, and some slide paths are gaining enough volume to run far into their runouts.  The dense and abundant snowfalls of this month are creating conditions that aren't typical for this time of year.  Give runouts a wider margin than you might expect.

Régions couvertes