Bulletin d’avalanche

Bitterroot

West Central Montana Avalanche Center
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Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

In the northern Bitterroot triggering a storm slab is possible in specific areas. Where there is 8" of fresh snow or more, stay alert for signs of instability, such as shooting cracks. Avoid steep convexities.

In the southern Bitterroot, isolated persistent slab could still be triggered on upper elevation north aspects.  Avoid slopes over 35º and areas of shallow snow. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    A surprise localized storm brought up to 10" of new snow to the northern Bitterroot yesterday. While the Savage pass SNOTEL indicates 0.8" SWE observations from the Brushy fork noted up to 10" of fresh by the end of the afternoon yesterday. The new snow fell on a variety of surfaces, including melt-freeze crust and surface hoar. As the storm snow consolidates, slab avalanches are possible.

    The consequences of a storm slab avalanche are higher in areas that received more than 8" of new snow. However terrain traps such as gullies that increase the consequences of all slides. Stay alert for signs of instability such as shooting cracks. Utilize safe representative test slopes such as small convex rolls to test the reactivity of the new snow to skiers and riders. Avoid convexities over 35º and terrain traps.

    (1/16/2023)

    A surprise storm left up to 10" in the Brushy Fork Monday 

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1–2

    Deeply buried facets may still exist on shaded upper-elevation terrain in the southern Bitterroot. The recent warm temperatures are helping basal facets bond. However, weak sugary facets can still be found below a cohesive slab in shallow north-facing terrain. It is unlikely to trigger this layer, but it could happen with just the right shallow trigger spot. Sledders high marking a slope may be able to trench down and trigger this layer. Avoid shallow areas in upper elevation north aspects, such as around wind-swept ridges.

    Isolated pockets of surface hoar exist throughout the Bitteroot. If you choose to ski steeper terrain, carefully assess the snowpack for a lower-density stripe of buried surface hoar. Use small, safe, and representative convex rolls to test the reactivity of the layer to skier travel. Avoid traveling in or above terrain traps. 

Avalanche Discussion

Overall the avalanche hazard is trending lower. Mild temps, calm winds, and isolated new snow have contributed to a mostly stable snowpack, with the exceptions noted above in the problems. Most notable is the surprise overproducing storm that hit the northern Bitterroot. Elsewhere, there is just enough reactivity and uncertainty in the upper elevation layers to keep it at moderate. Buried surface hoar is a tricky one, the touchiness dropped considerably over the weekend in both the Rattlesnake and Seeley zone, but it's still down there waiting for someone to hit the sweet spot and trigger it. Basal facets in the southern Swans and Southern missions remain a slight concern that is an unlikely but still plausible and high consequence problem.   At least in the Rattlesnake, the basal facets have bonded and become unreactive, so we can remove them from the problems list.  

Throughout the forecast area, crusts extend to 7000' and lower the possibility of avalanches at mid-elevations. Despite the low hazard, exceptions exist, and avalanche conditions could be found. Continue to stay alert to changing snow conditions and red flags as you travel.

The lower elevation snowpack, unfortunately, continues to shink. In the central Bitterroot, slopes are almost bare to 6000' on the south aspects and 5300' on the north. Wet loose avalanches have been a concern for the past week at lower elevations. Today temperatures should be cool enough today to keep snow surfaces mostly frozen. The freeze-thaw cycle has reduced the likelihood of natural loose wet activity if it does warm up. You could kick off small loose wet on steep slopes if temperatures climb higher than forecast.

We received a lot of high-quality observations over the weekend. Thank you to those who sent them in. You can submit new observations here.

Ski and ride safe

Régions couvertes