Avalanche forecast

Seeley Lake

West Central Montana Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Wind slab at upper elevation is the main concern today. The Rattlesnake and Seeley lake area contain the touchiest windslab, and small human triggered slides are likely just below ridgeline. The Bitterroot and Lolo saw less wind, but human triggered wind slab avalnches are possible. Avoid wind loaded slopes over 35º. Persistent weak layers continue to be a problem with avalanches possible on facets in the Rattlesnake, central and southern Bitterroot. 

Avalanche problems

  • Wind Slabs

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

    Wind slab can be expected throughout the forecast area. It is mostly isolated to upper elevations, although it can also be found mid-slope. 

    Winds are generally moderate today with strong gusts. Upper elevations will see stronger winds, and windslab will continue to build throughout the day. Westerly winds can be expected. This evening winds will shift to easterly in the northern portion of the forecast area. The Swans and east Rattlesnake will be most affected.

    Low-density surface snow will aid in the development of new wind slab as the day progresses.

    Look for cornices, wind lips, and drifts to indicate where wind slabs are present. Avoid wind-loaded slopes over 35º.

    Exercise more caution in the Rattlesnake and the Seeley Lake area, where stronger winds have occurred and wind slab is touchier.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2.5

    There are three separate persistent problems in different portions of the forecast area:

    • In the central Bitterroot, shallowly buried near surface facets failed and propagated 40 feet wide in steep terrain (>40º) Monday. The slide was of relatively low consequence, but the destructive size will quickly grow with additional loading from wind or snow. Avoid slopes over 35º where these facets are found. 
    • In the southern Bitterroot, facets in the old snow are still reactive. Yesterday, they were showing good likelihood of propagation in tests. They have been identified on northerly aspects above 7400 feet; however, they could exist outside of this as well. This is a low likelihood, high consequence layer. It’s best not to tease it; the right trigger point could cause avalanches up to 4 feet deep. Avoiding slopes over 30º where these facets are present is the best practice at this time. 
    • In the Rattlesnake, isolated basal facets exist. These are present at formerly windswept sites where snow remained after the early December thaw and in wind-scoured areas around rocks and outcroppings. Spots like the top of Too Steep to Tele and the south face Burgandy are great places to find these facets. The current cold temperatures are promoting further faceting.  Avoiding these areas is wise until they get buried deeper and have time to round out. 

Avalanche Discussion

In the past 48 hours, the forecast area has received about 2 inches of snow. The wind has been mostly light to moderate. Temperatures dropped to as low as -3ºF. 

Snow that sits on the ground changes; it’s always in a state of flux. So far this year, that change has been in a more stable direction. Mild temperatures and consistent snowfall promoted rounding and stabilization of the snowpack. The current drop in temperature and tapering of snowfall has the opposite effect. Faceting is taking place and slowly weakening the snowpack. This process is accelerated where the snowpack is shallow and where facets already exist. It will continue as long as the frigid temperatures are with us. 

With this change in metamorphism, we are seeing more complexity in the problems and decreasing stability in places. 

The persistent weak layer in the southern Bitterroot hasn’t improved and showed more reactivity in tests yesterday than in previous days, suggesting that the cold temperatures are having a negative effect in this area. This continues to be a low likelihood, high consequence layer worth avoiding. 

Shallow areas in the Rattlesnake now show faceting throughout the snowpack, rather than just at the base.

The near-surface facets that were the weak layer in a small slide at Gash Point on Monday may likewise be faceting further and have not improved. This layer is not consistent throughout the Bitterroot but is worth looking for wherever you tour. Check for a thin layer of sugary crystals 6” to 12” below the surface, and watch for shooting cracks as you tour.

Wind slab was a larger issue in the Rattlesnake yesterday than anticipated. Despite light winds, very reactive wind slab developed. The crown and debris from a likely natural avalanche were found on the northeast side of Point Six. Wind slabs were easily triggered, and shooting cracks were abundant. All slides were small, in the R1-D1 range, and isolated to just below ridgeline. However,larger slides are possible. Wind slabs, terrain traps, and frigid temps make a dangerous combination. 

The Missions and Swans have seen stronger winds and touchy upper elevation windslab can be expected there as well.

In the Camas Lake area, conditions were mostly stable except for thin reactive wind slab midslope, likely laid down by cross loading winds.

There are a variety of problems throughout the forecast area right now. In general, wind slab can be expected everywhere. Other persistent problems exist,  depending on where you are touring. Stay alert for changing conditions, use small safe representenative slopes for tests, and watch for features that indicate the presence of wind slab such as cornices, windlips, and stiff hollow sounding snow.  

Many thanks to the folks who have submitted observations. Please keep sending them in. You can submit observations here: https://missoulaavalanche.org/submit-an-observation/

Ski and ride safe.

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