Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
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Danger d’avalanche

Thu
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Very large natural avalanches have occurred on easterly and northerly aspects. The avalanche danger is trending down, however, winds and sun can amplify avalanche hazards in rocky, steep terrain, – especially in upper elevations. Be on the lookout for roller balls, point releases, or small pockets of wind-drifted snow.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    Starting a large, dangerous avalanche is becoming less likely as weak layers buried 2-4+ feet, slowly gain strength over time. Last Thursday, (March 2nd) a Wind Slab avalanche is suspected to have triggered a very large Persistent Slab slide that fractured approximately 1500 feet across and ran 2500 vertical feet. Most of the observed avalanches occurred on northern and eastern aspects above 5000 feet in elevation.

    Observing avalanches in nearby terrain is the most obvious way to be aware of your potential risk. For slopes without this kind of direct feedback, digging down into the snowpack to identify and test these weak layers is your next best option. Stack the odds in your favor and steer around thin wind-scoured or rocky areas, where the weak snow is closer to the surface. Choose slopes without convexities and overhead hazards to increase your safety margin.

    (3/7/2023) Far looker's left of the D3 hard slab on Nyack Photo: Adam Clark

Avalanche Discussion

The Persistent Slab problem remains in the Flathead Range, where the likelihood of triggering remains POSSIBLE. For many locations in the forecast zones, the weak layer is buried over 3 feet. Observers investigating the crown of a very large avalanche on the east face of Nyack concluded that the failure plane was faceted snow above the mid-January crust.

We have some uncertainty about the Persistent Slab problem in the northern Whitefish Range, due to limited observations and observations of a poor snowpack structure. Given these factors, we’ve listed the possibility for the Whitefish Range to be UNLIKELY.  We dropped the Persistent Slab problem from the Swan Range this past Sunday (March 5th), as we have not observed a Persistent Slab avalanche since February 10th. 

The next chance of snow is forecasted for the end of this week. The forecast for today is a mix of sun and high clouds.  If solar input exceeds expectations, watch for rollerballs and small point releases as your clue that instability is increasing. Steep rocky terrain getting hit by the warm sun will be the first to slide. Additionally, easterly winds capable of transporting snow are forecasted today. Based on our recent observations, there is limited available snow to transport, however, keep in mind that small pockets of wind-drifted snow may catch you by surprise. Plan your day to account for the possibility of sun and wind, so you have options to seek out shade and wind-sheltered slopes.

Our early March snowpack has caught up to the 1991-2020 median for SWE, with February’s mostly incremental snow showers. The higher end of SNOTEL gains in SWE start with Grave Creek going from 76% to 93% of the median, Stahl Peak: 86% to 94%, Noisy Basin: 107% to 114%, Flattop: 82% to 85%, and the site with the least change was Emery Creek: 74% to 76%. 

Fireside/Snowpack postponed to Wednesday, March 15. Join us for a virtual evening combining two of our favorite community ed workshops: State of the Snowpack and Fireside Chats. FAC forecaster Cam Johnson will be presenting the State of the Snowpack to help you digest the conditions and plan your next trip. Fireside Chats are an intimate, conversational forum for open dialogue about human and avalanche factors. With skier/psychologist Dr. Sara Boilen as our facilitator, we dig into the tough decisions, tricky snow, and lessons learned from a recent near miss. No registration is needed, click here for Zoom. Event will begin at 6 p.m. Thank you to the Whitefish Convention & Visitors Bureau for supporting our community engagement programs.

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