Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

The avalanche warning for the Whitefish Range has expired. Dangerous avalanche conditions remain as new snow and wind have built fresh slabs on leeward slopes. Slabs will increase in thickness with elevation. Cracking in the snow surface is a sign of instability. There have been numerous triggered slides over the past 3 weeks on weak layers buried 1-4' beneath the surface. Choosing low-angle slopes free of drifted snow is today's terrain choice.

Problemi valanghivi

  • Wind Slabs

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

    The Big Mountain is reporting six inches of fresh snow while Stahl Peak in the northern Whitefish picked up just a couple of inches. Winds have been moderate with strong gusts for several days. With additional fuel to add to the fire, expect to find fresh thin slabs capping thicker slabs formed over the previous days. Expect slabs to increase in thickness with elevation and found on the eastern side of the compass. They'll be considerably thicker in drifted areas such as downwind of ridgelines or cross-loaded gulleys. An avalanche in the surface snow can step down to a buried weak layer resulting in a large dangerous avalanche.  Cracking in the snow surface is evidence that you have found instability. Sheltered terrain should offer safer, less slabby conditions.

    (2/14/2021) Recent natural avalanches and localized cracking in wind drifted snow.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    Buried weak layers one to four feet beneath the surface are responsible for an impressive string of accidentally and remotely triggered slides over the past several weeks. New snow and wind are adding stress to these layers, and we assume there was a natural avalanche cycle overnight. Today, the potential for human-triggered slides has increased and these weak layers are at their tipping point. Dealing with this problem today is simple - stay off, and away from avalanche terrain. This includes low-angle slopes underneath, or connected to avalanche terrain, including runouts in the valley floor. Any terrain 30 degrees or steeper is suspect today. If you are not confident in identifying these slopes, you should not recreate in the backcountry today.

Avalanche Discussion

The National Weather Service forecasted an Atmospheric River to impact our area Monday into Tuesday morning. This large storm prompted us to issue an AVALANCHE WARNING for all zones yesterday morning, even though the bulk of the moisture was arriving later in the day and overnight.

The storm took its time to arrive but delivered well over an inch of water to the Swan Range, the Flathead Range, southern Glacier Park, and interior Glacier Park. The northern Whitefish Range was left nearly high and dry while the southern Whitefish Range picked up a respectable 6-8”. We have extended the AVALANCHE WARNING through tomorrow morning for all zones except the Whitefish.

We recommend that you avoid all avalanche terrain today, including slopes underneath or connected to avalanche terrain. If you can not identify these slopes, this is a day for you to avoid the backcountry.

FAC staff has been following the development of this storm for several days. It’s not that we were drooling over a big powder day but instead hoping for a heavy load to initiate a widespread avalanche cycle on our buried weak layers. We were hoping the steep slopes harboring buried weak layers would flush into the valley floor and relieve us of some of the anxiety we have with our Persistent Slab problem. Time will tell as to how much damage was done by this weather event. If you get out in the coming days and come across debris or note crowns, please fill us in on what you see. Observations from the public have been outstanding this season, and we ask for you to keep those obs heading our way.

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