Bollettino valanghe

Whitefish Range

Flathead Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
Open full map
Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Increasing winds will build varying layers of dense snow over stubborn drifts. Monitor density changes within the surface snow, especially as you climb in elevation.  Keep in mind that even brief periods of sunshine will increase avalanche hazards.

Problemi valanghivi

  • Wind Slabs

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

    Strong to extreme southwest winds occurred yesterday (Tuesday) morning. Tunnel weather station clocked winds at 100 mph at 5 am. These winds are clearly capable of transporting snow and have drifted snow into slabs above 5000 feet on typical leeward aspects. Early this morning, winds decreased and shifted to a northern and westerly flow. The forecast calls for increasing winds, that will transport modest amounts of available new snow (2 to 4 inches) and build layers of thin wind slabs throughout today.

    Expect to find wind slabs to be thickest, widest, and most common at upper elevations. To identify places within the terrain that may hold wind-loaded drifts, look for pillows or dune-shaped features near ridgelines, cross-loaded gullies, or around the sides of chutes.  While choosing terrain, think of the consequences of being knocked off your feet, dragged into a tree, or pushed over rocks. You can avoid the problem by choosing terrain where the snow is sheltered or being scoured by the wind.

    (1/1/2023)

    A well-developed cornice line from southwest winds cross-loading mid-elevations.

    Photo: Mark Dundas

  • Persistent Slabs

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

    Starting a large, dangerous avalanche on weak layers buried 2-4+ feet is unlikely. However, we are not out of the woods yet, as more intense solar radiation and recent winds increase the likelihood of cornice failure, or a small slab avalanche could potentially trigger these persistent weak layers.

    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.

    (3/4/2023)

    A very large D3 hard slab avalanche on Nyack Mountain. This slide was triggered during an intense wind storm on March 2.

    Photo: md

Avalanche Discussion

The wind is the primary driver of our avalanche problems today. The extreme southwest winds recorded on Tuesday morning, followed by increasing northwesterly winds today will warrant your attention. Anticipating conditions to change as you climb in elevation is a good start. Yesterday, observers reported stubborn drifts on typical leeward aspects. Today these drifts will be covered with building wind slabs from shifting west and north winds. Expect freshly formed wind slabs to be more sensitive to human triggering.

In addition to the listed avalanche problems, the potential for the sun to make an appearance is uncertain. Behind the scenes of writing this forecast, Cam and I have been pouring over weather models in the early morning hours, in the hopes of predicting this afternoon's mix of clouds and sun. It can be a challenge to accurately predict the timing and amount of cloud cover. More specifically, the angle of the sun in March has increased and solar radiation is far more intense today, as compared to mid-winter. Even short periods of sunshine pack a punch on warming the surface of recent snow. If we do see brief periods of strong solar input, be aware that avalanche activity may include loose wet slides and cornice falls. If you start to see roller balls on the slopes you are riding, get ahead of this instability and move to shady aspects.

Fireside/Snowpack Wednesday, March 15. Join us for a virtual evening combining two favorite community ed workshops. FAC Forecaster Cam Johnson will kick things off with a State of the Snowpack presentation to help you digest the current conditions and plan your next trip. Then we'll shift to Fireside Chats for open dialogue about human and avalanche factors. A recreationist, forecaster, and avalanche educator all experienced a near miss in the first three weeks of February. Together, Kat, Cam, and Meg will explore the tough decisions, tricky snow, and lessons learned from their experiences. No registration is needed; click here for Zoom. The event will begin at 6 p.m. 

Regioni coperte