Bollettino valanghe

Bitterroot

West Central Montana Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Triggering an avalanche is possible today along ridgelines and on wind loaded slopes. The best way to manage the hazard is to avoid steep wind loaded slopes and give cornices a wide berth. Cornices and wind slabs will start to grow again this afternoon as a storm begins to impact the region. Expect dangerous avalanche conditions to develop tonight into tomorrow. 

Problemi valanghivi

  • Wind Slabs

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

    Strong west winds and periods of snowfall over the last week created overlapping wind slabs on east aspects. Another layer of wind slab will start to grow this afternoon as a storm begins to impact our region. The avalanche danger will rise overnight, with the forecast calling for 6 to 12 inches of snow through Wednesday and strong west winds gusting to extreme. Stay alert for changing conditions, especially if the storm arrives early today. 

    Wind slabs appear smooth and rounded and are often found just below ridges and in cross-loaded gullies. Cornices, wind lips, and drifts all indicate wind direction and loading. Shooting cracks are a red flag that dangerous conditions exist, but you may not see them until you are on the slab and it is too late. 

    This wind slab problem is difficult to manage because any small fresh wind slab or cornice failure has the potential to step down to older wind slab layers and create a larger avalanche. The best way to mitigate this problem is to avoid wind-loaded slopes over 35º. 

    (2/6/2023)

    An overhanging cornice on the Point 6 ridgeline. 

    Photo: Arden Feldman

  • Cornices

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

    There are large overhanging cornices along most upper elevation ridgelines. Yesterday they were sensitive in the Rattlesnake, and today they will continue to grow. Give any cornice a wide berth, as cornices often break back further than expected. 

Avalanche Discussion

Strong west winds combined with light snowfall has been the theme over the last week. This pattern created a thick layer of overlapping wind slabs of varying stiffnesses and sensitivities on slopes facing the east half of the compass. The latest round of snowfall on Sunday night added yet another layer of wind slab. The Seeley Lake zone received 8-10 inches of snow, the Bitterroot 3-6 inches, and the Rattlesnake 1-3 inches. Winds were strong out of the west. Yesterday in the Rattlesnake, wind slabs were stubborn, but large overhanging cornices on ridgelines above were sensitive. 

A stronger storm will impact the region this afternoon through tomorrow. We can expect 6 to 12 inches of snow through Wednesday. The central and southern Bitterroot are favored for the highest snow totals. Yet again, strong west winds will accompany this storm system. Winds will gust in the extreme category. These winds will cause significant snow transport and wind loading. The winds may be strong enough to create wind slabs in unusual locations well below ridgelines. Expect the avalanche danger to rise tonight and tomorrow. Depending on the timing of the arrival of the storm this afternoon, fresh wind slabs may develop before nightfall. 

On Saturday in the central Bitterroot, a group experienced several significant collapses on an upper elevation south aspect. After digging a pit to investigate, they found propagating stability test results on facets just above a crust buried nearly 2 feet deep. The group made the wise decision to switch objectives and avoid avalanche terrain. This highlights the need to always stay alert for signs of instability, even when you don’t expect them. 

We have been fortunate enough to remove the persistent slab problems from the avalanche problem list. However, we still have a dry mid-winter snowpack with a variety of layers. In the southern Bitterroot, well-developed facets still exist near the bottom of the snowpack. In other areas, there may still be facets or surface hoar buried in the mid-pack. These layers are mostly unreactive and unlikely to fail. However, there is inherent uncertainty with low likelihood, high consequence scenarios like these. Snowpits can help you identify poor snowpack structures and double-check your assumptions. Be prepared to change objectives if you find unexpected unstable results or signs of instability. 

Let us know what you see today by submitting an observation. 

Ski and ride safe.

Regioni coperte