Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions exist.  The most hazardous terrain can be found on wind-loaded slopes and where you encounter 10 inches or more of storm snow resting on a weak snowpack (west through north through east aspects).  Avalanches may entrain more snow than expected as they run.  Expect avalanche conditions to worsen as the day progresses.  You can reduce your risk by avoiding travel on leeward terrain and by selecting simple, conservative terrain in sheltered areas. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    A month-long dry spell created a weak and highly faceted snowpack on west through north through easterly slopes.  A stormy period is now forming slabs above fragile, persistent weak layers.  Drifted terrain features will likely be the first locations for natural and human-triggered avalanches, followed by sheltered areas as slabs build.  Avalanches that fail on the highlighted aspects will likely entrain significantly more snow as they gouge into the weak snowpack and grow large.  Cracking and collapsing are clear signs that the snowpack teeters near failure.  

    Older, hard slabs exist below the storm snow on some leeward slopes and may create avalanches larger than expected.  Identifying these locations will be challenging now that the recent storm buried them.

    A photo of cracking and collapsing from the Thanksgiving storm.  Signs of instability like this are a clear indication to head for lower-angled terrain.

    Photo: Zach Guy

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Snowfall and wind may cause sensitive avalanche conditions in the storm snow.  Continued snowfall throughout the day will allow slabs to grow and become more problematic.  Aspects highlighted by the Persistent Slab rose are the most worrisome as avalanches can quickly grow in size by entraining old snow.  On sheltered sunny slopes, the new snow accumulates on slick crusts; avalanches on these slopes will likely involve just the storm snow and not gouge into the old snow.  You can manage issues in the storm snow by selecting slope angles less than 35 degrees and by avoiding steep slopes highlighted by the Persistent Slab rose.

    An example of small storm slab breaking earlier this winter.

    Photo: Zach Guy

Avalanche Discussion

Game on, folks!  After a months-long dry period, Mother Nature has returned the moisture flow to the area.  Storm totals as of 5 am are in the 6 to 10-inch range, with that amount possibly doubling by the end of the day.  Avalanche conditions are likely dangerous on many slopes early this morning, and the amount of dangerous terrain will increase throughout the day as snowfall stacks up. 

Do you remember several weeks of Dry Loose avalanches? Here are a few observations for a refresher (Snodgrass, Schuylkill Ridge, Axtell, Emmons, Elk Creek).  This weak snow is now being loaded by a substantial storm and will likely begin producing slab avalanches today.  Wind-drifted slopes showed signs of instability yesterday afternoon on Mount Baldy, so they will likely produce natural activity and easy-to-trigger avalanches today.  Avoiding wind-loaded slopes appears to be an obvious choice to reduce your risk.  

Predicting when slab avalanche activity begins on sheltered terrain is harder.  We have the well-documented weak layers on the Persistent Slab rose and a loading event; the question is when will the slabs begin to fail.  In the snow-favored Northwest Mountains, it seems probable that the problem exists this morning.  Storm totals will likely exceed 20 inches by the day's end.  In locations with lower storm totals, slab avalanches may be slower to develop.  A reasonable rule of thumb would be to expect slab avalanche behavior once 10 inches or more have accumulated in sheltered terrain.  Even if you find slopes with less than 10 inches new snow, you should expect Dry Loose avalanches to continue.  Any triggered avalanche on slopes with a weak snowpack will grow much larger than you expect as it entrains the weak faceted snowpack.

As snowfall continues throughout the day, avalanche conditions will worsen.  They will become more likely and grow in size.  Use caution as the day progresses and more snow accumulates.  You may find conditions have changed throughout the day, and slopes that were not problematic in the morning may be before the end of the day. 

Regioni coperte