Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
1 · Gering
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Kernpunkte

Five to 10 inches of new snow and strong winds will create dangerous avalanche conditions. Recent avalanches, shooting cracks, blowing snow, and heavy precipitation rates should all be signs pointing you towards simple terrain with slope angles less than 30 degrees. Drifting snow will thicken existing slabs sitting on an unpredictable weak layer. Give steep slopes that face north to east a wide margin for error today.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    New snow and strong winds will from slabs large enough to bury and injure a person. Due to high freezing levels, these slabs will get thicker and more dangerous the higher you climb. If you venture into leeward terrain, ride on slopes 30 degrees or less if you see new snow actively being transported by the wind. If we do receive the higher end of forecasted snow totals (8 to 10 inches), expect a storm slab avalanche problem to form on all aspects. Step back to lower-angled slopes on all aspects if this scenario plays out. 

    (3/14/2022)

    A person's weight was enough to trigger cracks in the new and recent snow at the snow surface Monday. Cracks like this are a clear sign a slab is present.

    Photo: Mark Dundas

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    We added Persistent Slab to the problem list because of a potentially dangerous and tricky weak layer buried 1 to 3 feet below the surface. There was a human-triggered avalanche failing on this layer yesterday (Monday) in the Whitefish Range and several on Saturday in all three forecast zones. Because of this weak layer, slabs may break far above you, wider than expected, and around terrain features. Triggered slabs of new snow could step down to this layer, creating a larger, more dangerous avalanche. Feedback that this problem exists may become more sparse the deeper it gets buried, and you may not get the feedback until it is too late and you are being carried down the hill. Allow this storm to test this weak layer, not you.

    (3/12/2022)

    A snowboarder triggered a small slab near the ridge that pulled out a thicker slab below the cliff band. The debris pile was heavy enough and large enough to crack the ice on the lake below. 

    Photo: Public

Avalanche Discussion

Weather:

Warm, wet, and windy! An atmospheric river is entering the region this morning. Weather models show .75 to 1 inch of water in each of the three forecast zones. This should deliver roughly a foot of new snow above 5500 feet by tomorrow morning. It does appear the Flathead Range and the Swan Range will see the upper end of snow totals. This storm will deliver strong wind speeds with gusts reaching 50 mph. The rain/snow line will be around 5500’ and drop later this evening.

Snowpack:

New snow and freshly drifted snow will be reactive to the weight of a human or machine. Slabs failing in the new snow will be anywhere from 6 inches to 2 feet thick. Leeward facing slopes will be the first to become unstable given the strong wind speeds. Keep a close eye on new snow accumulations. A storm slab problem may develop by the end of the day in areas sheltered from the wind. Long cracks or shooting cracks around your boards or machine are signs you have found a slab. You may also see rollerballs and small wet loose avalanches around 5000 feet where rain lands on newly-fallen snow. 

A dangerous and potentially tricky layer of buried near-surface facets lurks roughly 1 to 3 feet below the surface and will get buried deeper throughout the day. This problem is currently more of a concern on north to east facing aspects that did not receive a sun crust. Yesterday (Monday) a skier triggered a 6 to 10-inch slab that likely failed on this same layer in the Whitefish Range. Additional weight may increase the sensitivity and likelihood of triggering a slab breaking further down in the snowpack. If triggered, slides will likely run far and fast since they will be sliding on a slick rain crust. They may also break far above you and wrap around terrain features.

Travel Advice:

I highly recommend giving avalanche-prone slopes that face north to east a day off today. Earlier in the day, safer aspects will be windward slopes that face south and west, or slopes sheltered from the wind. As the day progresses and 8 or more inches of snow begins to pile up, adjust accordingly and dial back your slope angle on all aspects and minimize overhead hazard. Have a dynamic approach to today and be aware of changing conditions.

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