Avalanche forecast

Rattlesnake

West Central Montana Avalanche Center
View on map

Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
1 · Low
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Out of date — this forecast expired 4 years ago.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

Riders are most likely to trigger small wind slabs on upper elevation east aspects today. Avoid wind-loaded pockets over 35º.  Buried surface hoar is gaining strength and is stubborn but triggering a slide on this layer remains possible. Avoid steep convexities and unsupported slopes. 

Avalanche problems

  • Wind Slabs

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

    Moderate winds with strong gusts out of the west have built windslab on upper elevation easterly aspects that will grow throughout the day.  Just below ridgeline and along the leeward side of gullies is the most likely place to find wind slab currently.  As this evening's storm arrives, winds will increase, windslab will grow more rapidly, and become more widespread in distribution.

    Cornices, wind lips, and drifts all indicate wind direction and transport. Wind slab will be stiff and hollow sounding. Shooting cracks are a red flag that avalanche conditions exist, but you may not see them until you are on the slab and it is too late. Test small safe, representative slopes before moving into bigger terrain. The best way to mitigate this problem is to avoid wind-loaded slopes over 35º. 

    (1/20/2023) Photo: Jeff Carty

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    In the Rattlesnake a layer of  surface hoar  is buried up to 18" deep. 

    The reactivity of this layer is rather patchy, with no alarming test results or slides noted in the West Rattlesnake. As of Wednesday the overlying snow was not consolidated enough to form slab, but may have stiffened enough to propagate. 

    In the east Rattlesnake, the last skier-triggered slide was reported at Wisherd Ridge on Sunday; the structure for skier-triggered avalanches is there, but better bonded than six days ago.  Given the nature of buried surface hoar triggering a slide is still possible. However, we are not seeing obvious signs of instability like shooting cracks, so it feels stable despite the lurking weak layer.

    You are most likely to find the buried surface hoar above 7000' on north and east aspects. The best way to manage it is to avoid slopes and convex rolls over 35º. 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. You probably won't get red flags like shooting cracks or whumpfing, but if you do, step back to mellower slopes. 

    (1/15/2023)

    Skier triggered avalanche on Wisherd Ridge

Avalanche Discussion

Since the last forecast, some snow has trickled into the northern portion of the forecast area. The Seeley zone received around 4”, the Rattlesnake around 3”, and the northern Bitterroot closer to 5”. The central and southern Bitterroot was passed over and received no new snow. 

Winds picked up in the same areas that received snow, and fresh windslab was building in Seeley the Rattlesnake and northern Bitterroot. The central Bitterroot had light snow transport at ridge top yesterday, while the southern Bitterroot remained calm. 

The Seeley and the Rattlesnake have mostly uniform conditions, with buried surface hoar and winds slab throughout each zone. The Bitterroot feels like three distinct zones currently, with widespread surface hoar buried up to 17” deep in the northern Bitterroot, generally stable conditions in the central part, and a shallow snowpack with lingering, deep persistent slab in the southern portion.

Today, our primary avalanche concern has shifted to windslab. It will continue to build with moderate winds and strong gusts. With the storm's arrival this evening, winds will increase to over 30mph throughout the forecast area. The avalanche hazard will rise to considerable in wind loaded terrain on Sunday. 

We’ve removed loose dry avalanches from the problem list. The surface snow has consolidated enough to limit sluffing to very steep and isolated terrain.  

Public observations are very important to understanding conditions. Please submit an observation and tell us how much new snow and wind you see over the weekend. 

Ski and ride safe

 

Regions covered