Bollettino valanghe

Gunnison

Crested Butte Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

A weaker overnight refreeze and above-normal temperatures today will shorten your window for stable corn riding.   This morning, the avalanche danger is Low and will rise to Moderate before noon as the snow surface heats up.  Start and finish your day early or move to less consequential terrain once the snow surface starts to rollerball, pinwheel, or thaws to more than ankle-deep wet snow.  Concerns for larger and harder-to-predict wet slabs and cornice falls are increasing. Old dry slabs have become increasingly rare but remain an isolated threat on high, northerly aspects, especially on rocky or shallow slopes.   

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    High-consequence persistent slab avalanches have become isolated and difficult to trigger.  The last persistent slab triggered in our forecast area was on April 3rd.  The most problematic terrain is on high elevation, northerly aspects in areas with relatively shallow snowpacks (<175 cm).  Old facet layers are weaker and easier to impact in steep rocky slopes with variable snow depths.   This video highlights this type of terrain. 

    Persistent slab avalanche crowns spanning steep, rocky terrain on a north facing, alpine slope. This avalanche ran sometime during the late March storm cycle and wind-loading event.  

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–2.5

    There's a small chance for natural or triggered wet slab activity today.  The above-normal temperatures are causing meltwater to flow deeper into the snowpack towards old weak layers.  Meltwater can cause weak layers to fail, resulting in surprisingly large wet avalanches.  Although predicting the timing and location of wet slabs is difficult, you can reduce your risk by traveling early in the day while snow surfaces are still frozen or just starting to soften.  Move to colder aspects or lower angle slopes if you are sinking more than a few inches into a wet snowpack.   High-elevation, northerly aspects do not have enough meltwater for this problem to develop yet, and low-elevation southerly aspects have already seen water drain through the snowpack, reducing the threat.  

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Watch for shallow sluffs in the upper snowpack as it gets wet from solar radiation and warming temperatures.  Instabilities will be easy to recognize: look for rollerballs, pinwheels, or sluffing from very steep slopes.  Use sluff management techniques or move to lower slope angles to manage the problem if it develops.  Even though most wet sluffs today are expected to be relatively small, they can pack enough punch to carry you down a gulley, over a cliff, or into trees. In isolated areas, a wet slide might gather enough volume to be large in size.  You can avoid the issue by moving to colder aspects where the snow surface is still frozen or just starting to thaw.  

    One of the larger wet loose avalanches observed this week.  Note how the longer and steeper the terrain is, the more snow it entrains.  

Avalanche Discussion

Yesterday's soaring temperatures caused surface melt and wet loose instabilities to expand to more above treeline slopes and some northerly aspects up to 11,000', while mobilizing free water deeper into the snowpack (see video).   Overnight temperatures dropped to just below or just above freezing; our weakest freeze of the week.  Cloud cover diminished after midnight, allowing enough radiative cooling for a surface refreeze.   The avalanche danger is Low this morning while that crust maintains the strength and stability of the upper snowpack.   Once that crust thaws to wet or mushy snow, the danger will rise to Moderate with the increasing threat of wet avalanches.  The most common instability will again be shallow wet loose activity similar to what we have observed this week.   The above-normal temperatures are increasing the threat of larger avalanches, such as cornice falls, gouging wet loose avalanches, or wet slabs.  These problems are more difficult to predict, but are more common later in the day during or after peak daytime heating.  If you are getting a late start today, west-facing terrain is the last aspect to thaw, and high northerly slopes are still holding dry snow or just shallow moistening. Stay cautious of those unusually shallow and rocky slopes on high northerlies where early-season facets are weaker and easier to impact, and don't dilly-dally below cornices.  

A similar pattern requiring early starts is expected tomorrow.  Because we already saw a significant warmup last week which gave the snowpack its first shock, we are expecting to survive this one without a large wet cycle.  We'll monitor for evidence to the contrary today, and we could bump the danger rating up tomorrow if we see a pattern of large activity developing this afternoon.  Stay tuned.  

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