Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
Voir sur la carte

Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
Open full map
Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Heavy snowfall and intense wind loading yesterday will make avalanches easy to trigger today.  Wind-loaded slopes are dangerous, evidenced by large to very large avalanches that ran naturally yesterday.   You can also trigger a large avalanche on wind-sheltered slopes on the north half of the compass on a layer of buried surface hoar.   Although southerly aspects protected from yesterday's winds are the safest option, stay alert for unusual cross-drifting patterns even at low elevations or shallow instabilities as the new snow moistens.  Conservative terrain choices will help you defend against a snowpack that is reeling from yesterday's hard-hitting storm.  

Problèmes avalancheux

  • Persistent Slabs

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

    Heavy snowfall and intense wind loading yesterday added significant amounts of stress to weak layers in the snowpack, causing large and dangerous natural avalanches.  Avalanches breaking on old weak layers will be more sensitive to human triggers now that the snowpack is stressed.  The most prominent and active weak layer is buried surface hoar several feet deep on the north half of the compass. There is also potential for avalanches to break on faceted crust layers on some higher, southerly aspects, or depth hoar layers near the ground.  Persistent slab avalanches can be remotely triggered from low-angle terrain and break larger and wider than you might expect.  Low-elevation southerly aspects are significantly less problematic, and slope angles consistently less than 30 degrees are a reliable way to avoid the problem.  

    A broad avalanche on the north side of Crystal Peak that ran during last week's storm.  

  • Wind Slabs

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

    Intense wind drifting yesterday formed slabs of varying thickness on wind-loaded terrain features at all elevations.  Yesterday's winds shifted from southwest to northwest, so you will most likely find slabs on the east half of the compass or cross-drifted features elsewhere.   Use visual clues to identify where drifting snow landed: it will look and feel deeper, stiffer, and more rounded.  Some of these slabs will be hard and stubborn already, others are easy to trigger.  You can avoid the problem and find softer, higher-quality snow in wind-sheltered terrain.  Consider slab size and terrain consequences before crossing a drifted slope. Avoid steep slopes where fresh wind loading overlaps with larger persistent slab issues; triggered slabs in the upper snowpack can step down and produce much larger avalanches. 

Avalanche Discussion

Yesterday's violent cold front delivered an additional 6" to 12" and provided the fuel for intense wind drifting through the day (see video).  Visibility was limited, but a few notable avalanches were reported.  Mt. Axtell's Green Lake Bowl produced a very large avalanche that failed on weak layers near the ground, cleaning out the entire snowpack. Ugly! A large avalanche ran off of a windloaded slope on Ruby Peak.  Gibson Ridge produced a large avalanche that likely broke on our buried surface hoar layer.   And outside of our forecast area, the north chute of Park Cone buried Taylor Canyon Road with about 6 feet of debris.  Naturals are possible today under rapid solar warming or if winds continue to drift snow this morning. Our forecast team will be out documenting recent natural avalanche activity with today's clear skies. Drop us a photo ([email protected]) or observation on our website if you see something interesting.  

There are two types of slopes where you are most likely to get into serious trouble today.  The first is on a windloaded slope, which you can visually identify by paying attention to terrain characteristics, drifting patterns, and snow surface characteristics.  Avalanches on windloaded slopes could involve wind slabs of varying thickness and hardness, or given the immense amount of insta-stress delivered by yesterday's winds, there's a good chance leeward slopes can fail on one of the many weak layers in our snowpack. Mt. Axtell is a prime example of a worst-case scenario.  Winds were blowing snow at all elevations yesterday, so be alert for drifting in unusual locations, even near valley bottom.  

The second, and more deceptive troublemaker is on wind-protected terrain on the north half of the compass.  That's where our surface hoar layer is quietly lurking.  The Gibson Ridge slide is a great example.  Yesterday's additional snowfall will make those layers more reactive today than they were earlier in the week.  I'm most nervous about slopes in the Southeast Mountains because slabs are still an ideal thickness for human triggering.  In the deeper zone, slabs are thick enough that human triggering typically requires hitting a shallow spot on the slope, a step-down avalanche, or an abrupt convexity where those layers are more susceptible to triggers.  

Events: The CBAC Fireside Chat Series presents legendary American alpine climber George Lowe on Sunday, March 3 at the Mallardi Cabaret Theatre in downtown Crested Butte at 6 p.m. Best of all, it’s free!

Régions couvertes