Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

If someone warned you that you are likely to get shot if you went into your favorite bar today, would you still go in for a beer?   Ask yourself that question if you are eyeing a steep slope.  Very dangerous avalanche conditions are real today: a cycle of large natural avalanches is likely continuing after a foot of snow and increasing winds last night.   In or next to steep terrain, you are likely to trigger a slab avalanche several feet thick at any elevation, and especially on terrain that faces towards the east. Windloaded terrain is very dangerous.   The low angle powder is riding great on all aspects and across the entire forecast area.  Avoid avalanche terrain to make it a fun and safe day in the backcountry.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3

    To avoid an easy-to-trigger slab breaking on buried weak layers, choose terrain that is consistently less than 30 degrees with no overhead hazards.  Dozens of slabs up to several feet thick and hundreds of feet wide have been triggered or run naturally this week.  While persistent slab activity has occurred on all aspects, slabs are most widespread and reactive on the eastern quadrant of the compass, where winds are loading thicker slabs.  You can trigger a dangerous avalanche while riding in on a steep slope, or remotely while traveling adjacent or below steep terrain.  In the Northwest Mountains, avalanches are likely to fail naturally today where winds are loading start zones. Some of these could run long distances.  

    2/4: A very large avalanche in Red Lady Bowl that was remotely triggered. ENE Aspect, NTL.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    With up to 14" of fresh snow and winds increasing through the night, natural and easily triggered slabs of drifted snow will be ongoing.  Avoid wind drifted terrain today: fresh wind slabs will be dangerous by themselves, or they could step down and trigger a much larger persistent slab avalanche.  Blowing snow and deep-looking deposits of drifted snow are clues to identifying the problem on the surface.  Wind slabs will be forming below ridgelines, in crossloaded gullies, and below rock bands or rollovers.   

Avalanche Discussion

Northwest flow over delivered again!  Irwin study plot is showing 14" of new snow: anticipate higher than expected storm totals extending across the Ruby Range similar to last weekend. The rest of the forecast area saw 2" to 6" of snow.  More importantly, northwest winds are peaking this morning - their highest wind speeds since the big storm on Wednesday night.  Alpine wind speeds are blowing 30 mph and gusting into the 50's, and they have plenty of low-density snow to transport.  

Since last Saturday, we have documented 140 human-triggered and natural slab avalanches in the Crested Butte area.  96 of the avalanches this week were easily large enough to bury or kill someone (D2 to D2.5 in size).   Two of these were large enough to destroy a wood-framed hose (D3 in size). We should see plenty more activity because of last night's snow and increased winds.  In the past week, there have been four avalanche fatalities in Colorado, all involving large persistent slabs.   The danger has been pegged at HIGH since Wednesday evening.  The danger remains HIGH in the Northwest Mountains today, where the snowbelt saw surprisingly large snow totals last night.  The danger is only slightly lower in the Southeast Mountains.  We have uncertainty on how extensive ongoing natural activity is at upper elevations where winds are rapidly loading the snowpack.   

Avalanches have mostly been breaking on the layer of facets and faceted crusts that formed during our three-week dryspell January (1/19 layer).  In a few cases, they are stepping down to basal weak layers near the ground.  Slabs range in size from 7 feet thick or more on high elevation, windloaded terrain of the Northwest Mountains down to a foot or two thick at low elevations in the Southeast Mountains.  Pick your poison: the smaller slabs are easier to trigger, the larger slabs are more stubborn but are unsurvivable.  Avalanches that run naturally from windloaded, high elevations could be very large and run long distances.  

When I write forecasts, I like to offer lower-risk terrain ideas for people looking for steeper terrain.  There aren't many right now.  Slabs are less widespread on windward terrain, especially in the Southeast Mountains.  Mid to low elevations that face the south quadrant of the compass have several crust layers in the upper snowpack that are helping add strength to the equation.  Apart from these exceptions, if you venture onto steep terrain, the odds of triggering a deadly avalanche, or being overrun by a natural, are about as bad as they've been all winter.  The eastern quadrant of the compass (NE, E, SE aspects) is where you are most likely to get into trouble. That's where slabs are thickest, most widespread, and most stressed from last night's winds, and where weak layers are most continuous and fragile.   This diagram depicts the number of observed slab avalanches in each aspect and elevation band since our January 19th layer was buried.

It's not all doom and gloom though.  There is high quality powder on all aspects, and the snow is riding fast enough that low angle terrain is a blast right now. The last few storms finally spread the wealth to the Southeast Mountains.  This is the best coverage and most widespread powder conditions we've had all season.  Thus, opportunities abound for a fun, low-stress day with your friends on slope angles less than 30 degrees while minding your overhead hazards.  That's exactly the type of terrain I'm heading to today. 

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