Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Start and finish your day early for safer riding.  The avalanche danger could rise to Considerable as Thursday's warmup increases the threat of large natural wet avalanches and cornice falls. Choose more conservative terrain after surface crusts thaw into more than a few inches of wet snow. This video describes wet snow strategies.   At higher elevations on northerly aspects, you can still trigger a dangerous slab avalanche several feet thick, exemplified by Wednesday's close call on Whetstone.   

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–3

    Snow and wind-loading last week formed a new generation of slabs up to several feet thick over small-grained facets in the upper snowpack.  Numerous large slab avalanches have occurred on this layer in the past week.  Slabs are larger and most active near and above treeline on wind-loaded slopes on colder aspects.  For a safer day, avoid previously wind-loaded slopes, while staying alert for potential instabilities on wind-sheltered terrain.  Persistent slab avalanches are unlikely on slopes with a thick surface crust (south half of the compass early a.m.) and at low elevations.

    On unusually shallow slopes, most commonly in the Southeast Mountains, there is still a small potential to trigger a destructive avalanche that breaks on deeper weak layers. The most concerning structures are on northerly aspects near and above treeline where snow depths are less than 170 cm, or where large cornices fall onto slopes.  

    A large human-triggered persistent slab on Whetstone on Wednesday.  

  • Wet Slabs

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

    This week's warmup is causing meltwater to drain toward buried crusts and weak layers deeper in the snowpack.  This is increasing our concerns for large and difficult-to-predict wet slabs to release later in the day.  Only some slopes getting flooded by meltwater have poor snowpack structures capable of producing wet slabs; those are most common on "shoulder" aspects facing east or west.  Although instabilities are difficult to identify once the snowpack gets wet, you can avoid the problem by traveling early while surface crusts are frozen solid or just starting to thaw.  

  • Loose Wet

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

    Warming temperatures and strong solar radiation will wet snow surfaces first on east, then south, then west-facing terrain, increasing the threat of natural and triggered wet loose avalanches.  Most slides will start shallow, but some could entrain dangerous amounts of wet snow during or after the hottest part of the day as the snowpack becomes more saturated.  Travel in steep terrain before surface crusts thaw into pushy wet snow.  Move to colder aspects or lower slope angles to avoid the problem after it develops.  

    Natural wet loose activity that ran on Wednesday.  

Avalanche Discussion

Although we have a complex list of avalanche problems on Thursday, you can avoid all of them by traveling early on the south half of the compass in pursuit of good corn riding.  The danger will rise towards Considerable as the day warms up, provided cloud cover is minimal.  Don't outstay your welcome in steep terrain once the thermostat soars to our highest temperatures of the season.  We observed an uptick in D1 to D1.5 natural wet loose activity on Wednesday.  With warmer temperatures on Thursday, wet avalanches are expected to become larger and/or more frequent, and we may see some wet slabs. Last week's wind event buried another dust layer near the snow surface, which is starting to emerge on some slopes and will accelerate surface melt.  Although we always have uncertainty forecasting for the initial onset of deeper gouging wet loose avalanches or wet slabs, they are a fairly easy problem to manage with spring travel protocols.  Exit steep terrain before you are sinking past your ankles in wet snow.  

The danger is less dynamic on northerly facing terrain near and above treeline, where the snowpack has remained dry.  An early start won't beat the persistent slab problem that continues to rear its ugly head.   On Wednesday, someone triggered and was briefly caught in a large slab avalanche on the north side of Whetstone.  A forecaster on Tuesday experienced a collapse and propagating test results near Mount Baldy.  Look at the pattern of large natural avalanches from the past week to identify the most problematic terrain.  Any large cornice fall from rising temperatures could also trigger a persistent slab.    On the same northerly aspects below treeline, slabs are less developed, and weak layers are less common. Only a few human-triggered avalanches have occurred since our near-surface facets and faceted crusts were buried on March 23rd.  Stay alert for isolated instabilities on unsupported rollovers or previously drifted features at those lower elevations.   

Friday's temperatures will be similar but with stronger winds, and some increasing cloud cover.  Wet problems aren't expected to be as dangerous at upper elevations because of this. However, lower elevations will see their worst refreeze of the week with some cloud cover expected Thursday night, which could magnify wet issues down low. 

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