Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Reports continue to trickle in of human triggered avalanches large enough to bury, injure, and kill someone. Warming temperatures and sunny weather will increase the likelihood of human and natural avalanches today. Plan your day to be out from under large, south-facing avalanche paths and stick to slopes that are less than roughly 35 degrees. Slopes sheltered from the wind with consistent slope angles are your best bet for a safe day.

Problemi valanghivi

  • Persistent Slabs

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

    The previous storm slab problem is our new persistent slab and is here to stay. Remotely triggered avalanches, shooting cracks, and spooky snowpack tests are all recent signs that should make you choose simpler terrain.  Weak layers buried up to 2 feet deep prove to be reactive to the weight of a person and large enough to bury and injure you. This problem is most common where the wind has stiffened snow into thicker, more dangerous slabs. Warming temperatures and solar input will increase the likelihood of triggering a slab avalanche today. 

    Debris from a human triggered avalanche on January 30th.

  • Loose Wet

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

    South-facing aspects that receive direct sunlight can produce avalanches large enough to bury or injure you. Warm temperatures alone may produce avalanches on northerly aspects at low elevations. Rollerballs or pinwheels are signs that conditions are ripe for wet loose avalanches. If you see these signs, avoid being on or underneath avalanche terrain with similar characteristics to the one that was rollerballing. To reduce your risk of this problem, seek out shaded, northerly facing slopes at mid and upper elevations. Plan your day and exit accordingly to be out from underneath south and southwest facing avalanche paths in the afternoon.

    Wet debris from 1/13 avalanche cycle.

Avalanche Discussion

Today we are in a “high-end moderate” kind of day. Certain atmospheric conditions have and will bump up the likelihood of triggering an avalanche. Let’s break apart current conditions and how the day can unfold.

Each day for the past three days, riders have triggered slab avalanches throughout the forecast area. Two of these were remotely triggered (triggered from a distance) and were large enough to bury a human, shown here. Here are more observations from the Whitefish Range and another one from the Flathead Range. These avalanches were all accompanied by shooting cracks, ran long distances, and triggered on convex rolls or in wind loaded terrain. This should steer us to planar slopes that are sheltered from the wind. So, how can this problem change today?

Let’s start with warming temperatures and solar input. If the weather forecast verifies, which I have stated a couple “ifs” around this topic, we will likely see a round of natural avalanches. Currently, we have a COLD, dry upper snowpack. This cold snow is sitting on a weak layer above one of the slickest, hardest crusts I have ever seen. Warming temperatures and solar input can stiffen the slab and make triggering more likely. Solar facing slopes sheltered from the wind will likely become wet and begin to rollerball and slide on the crust. These can run far distances, and wet debris is nothing I care to tango with.

Next, let’s go to winds. Yesterday afternoon winds picked up and were blowing at speeds optimal for transporting snow. Aeneas (Swan Range) averaged in the 20s, and Snowslip (Glacier National Park) averaged in the high teens. This bump in wind speeds drifted snow into thicker, more dangerous slabs on slopes leeward to the wind. I would expect to see slabs failing on the same layers of buried surface hoar and near-surface facets on or near the 1/13 crust. This piece of information cues me to stick to sheltered slopes and out from underneath leeward facing start zones. Remember, remotely triggered avalanches have occurred in the last three days. Your best and safest riding conditions will be found on northerly facing aspects with slope angles less than roughly 35 degrees.

Regioni coperte