Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
View on map

Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Wind-sheltered terrain with a deep and uniform snowpack offers the safest riding today.  Sensitive wind slabs have formed a relatively small hazard in leeward terrain at higher elevations, exemplified by several skier-triggered slides yesterday (Ruby, Schuylkill).  In the Northwest Mountains, persistent slabs are becoming increasingly isolated and unreactive.  To guard against a very rare but dangerously large avalanche, choose routes that minimize exposure to shallow and rocky areas.  

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Observers yesterday triggered a handful of fresh wind slabs 6" to 12" thick.  Northwest winds are forecasted to increase later today, which will thicken yesterday's slabs or form a fresh batch.  Wind drifts are most common below ridges, in crossloaded gullies, and below abrupt rollovers.  Be especially cautious in large or consequential terrain.  Cracking snow and blowing snow are signs of instability.  Most slabs are expected to be small, although there could be isolated exceptions in terrain with large fetches.  

    1/24: A skier triggered wind slab that broke about a foot thick on Ruby Peak.  

  • Persistent Slabs

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

    On most slopes in the Northwest Mountains, faceted weak layers are buried deeply and unreactive to human triggers.  Some slopes have unusually shallow or variable snow depths where riders may be able to trigger a hard slab several feet thick or more.  Be cautious of windward terrain features with variable depths, rock bands, and slopes that previously avalanched in early December where you are most likely to find a thin trigger point.   The safest riding is where the snowpack is uniform and consistently deeper than about 5 feet (150 cm).  

     

    This large avalanche failed on Ruby Peak around January 18th.  This exemplifies the type of terrain with lingering concerns.  It's a windward slope with below average snow depths and numerous rocky areas.  

Avalanche Discussion

We are keeping the danger elevated in the Northwest Mountains today because yesterday's observations suggest that wind slab formation was a bit more widespread and reactive than anticipated.  Winds are expected to increase again later today, which will continue to fuel the problem.  Some drifts will be stubborn today, while others are forming over a reactive weak layer of near-surface facets that formed during our recent dry weather.  You'll need to manage this problem using visual clues and feeling for thicker drifts if you are riding in large or consequential wind-exposed terrain.  

The relatively quiet weather of the past week has given weak layers near the ground a chance to recover and adjust to the month-long loading period.  Our forecast team has been discussing whether we can phase the persistent slab problem off the list in the Northwest Mountains.  Our pit work yesterday on Ruby Peak suggested layers are becoming unreactive, while explosive work at Irwin yesterday produced some deep cracking and a large collapse with a hand shot.  That suggests that we aren't quite out of the woods yet in the deep zone:  there still may be a few slopes out there that could bring down the house if you hit a shallow trigger point.  The easiest solution to safeguard against that very low likelihood but high consequence threat is to ride where the snowpack is deep and uniform.  In parts of the Southeast Mountains, it's an unhappier story, where the snowpack has remained thinner and weaker this season.    For example, stability tests near Red Mountain on Tuesday produced unstable results on both of our prominent weak layers in the lower snowpack, both at ideal depths for human triggering.   Although there's a lot of variability across the Southeast Mountains right now, stability involving deep layers is generally improving.  You'll want to assess each slope on a case-by-case basis.  This map of modeled snow depths around our forecast area paints a generalized picture of the deeper and more trustworthy areas vs. the have-nots.  The goldilocks snow depth for finding the most troublesome structure seems to be around 3 to 4 feet (90 to 120 cm).  

Regions covered