Boletín de aludes

Flathead Range & Glacier NP

Flathead Avalanche Center
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Peligro de aludes

Sun
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The warmest weekend of the season is upon us, and wet avalanche problems may develop quickly as the day heats up. An unsupportable surface crust and mashed potato-like snow are clues directing you to move to a different slope. Limit your time spent below corniced ridgelines and steep sunny aspects. Choose lower-angled terrain to enjoy today's spring weather safely.

Problemas de aludes

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Today's warm temperatures will increase the instability of the surface snow. A poor refreeze overnight will allow the surface crust to break down earlier than it experienced yesterday. Dry snow on northerly slopes at upper elevations may warm for the first time. You can trigger a slide on slopes steeper than 35 degrees in areas where a supportable crust does not exist. You have worn out your welcome if you find yourself in thick mashed potato snow. Rollerballs may develop in areas harboring dry snow and are a clue that the surface is becoming unstable. Move to a different aspect or elevation band before conditions worsen. Limit your time spent on or below sunny slopes this afternoon.

    (3/24/2022)

    Recent warm temperatures and solar input initiated slides large enough to bury, injure, or kill a person.

    Photo: Mark Dundas

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–3

    Weak layers 1-3 feet below the surface still have the potential to result in a slab avalanche. A rider's weight or snowmachine may affect these layers resulting in a slide. A cornice fall or wet loose slide could be enough mass to trigger an avalanche. Choose planar or concave slopes to maximize your chances of having a safe, uneventful day. Limit time spent traveling beneath steep slopes, especially as the day warms up and the surface crust breaks down.

    (3/23/2022)

    This very large natural avalanche (HS-N-R3-D3-O) released on the afternoon of March 23. It may have been triggered by cornice fall. The slab intially released on a near-surface weak layer, then stepped down to a more deeply buried layer. The avalanche occurred on an east-facing, upper elevation slope on Mt. Cameahwait.

    Photo: Adam Clark

  • Cornices

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Sizeable seasonal cornice formations exist on many upper elevation ridgelines in all mountain ranges. These behemoths generally require sustained warming before they fail. Today is the fifth day of continued warm weather, and the likelihood of failure is increasing. If cornice sections begin to calve off, van-sized chunks of snow may trundle down the slope. This trigger's impact pressure and sheer mass may initiate a large slab avalanche on a buried weak layer. While traveling along ridgelines, give these features a wide berth because they are notorious for breaking further back than anticipated. Limit your time spent on slopes beneath these beasts.

    (3/17/2022)

    Large seasonal cornices are found along many ridgeline locations.

    Photo: Adam Clark

Avalanche Discussion

The prolonged heatwave, which began Tuesday, will continue through Sunday. Temperatures Friday reached their highest of the season at many mid and upper elevation weather stations. Low to mid-40s F were common between 6000 - 7000 feet. The cool spot was the Mt Aeneas ridgeline station at 7186 feet, only reaching 35F. Today's highs should surpass Friday's, with Sunday's even warmer and approaching record high temperatures. 

Mountain weather stations dipped below freezing Thursday evening and stayed there for 12-16 hours. The result was a solid refreeze of the snow surface, which allowed for fast traveling in the morning before the crust started to break down in the afternoon. Unfortunately, we will not be so lucky today. As of 0400, a handful of stations between 6000 - 6800 feet recording above freezing temperatures. Stations that dipped below freezing occurred at a later hour and were warmer than Friday. Today's crust will be thinner, less supportable, and break down sooner than experienced Friday.

Unusually warm temperatures are on tap for the next two days. This weekend's mantra should be "Unusual conditions produce unusual avalanches." Expect the unexpected despite an avalanche danger rating of MODERATE, or Level 2. Northerly slopes, especially at upper elevations, still hold mostly dry snow. Today's warmth may be enough to start a natural wet loose avalanche cycle in this relatively dry snow despite limited solar input. Triggering a slide in mushy snow on southerly slopes at mid and upper elevations will become more likely as the day progresses. Water percolating into the snowpack may initiate wet slides on buried weak layers. The likelihood of cornice fall is increasing. To get through these challenging conditions, choose terrain less than 35 degrees in steepness free from overhead hazards. 

Observations were limited Friday, but an observer at Scalplock, in Glacier Park noted a supportable crust and no signs of instability during their tour early in the day. Another party visited Mt Brown in GNP and found cold conditions at upper elevations and fun corn snow at mid-elevations. The Swan Range has been a black hole for observations, but a group visited Noisy Basin and found a supportable crust to 7000 feet on sunny aspects in the morning and a paper-thin crust capping dry snow above 6000 feet on northerlies.

Do you know that we produce a text and video weekly summary of snowpack, weather, and avalanche conditions? You can find this in the Conditions Blog below the Bottom Line or here. Megan, the FAC March intern, wrote this week's summary before heading back to grad school in Oregon.

Join us for our last education event of the season. Topics Class! The Scoop on Spring Touring, Wednesday, April 6th, 6:30 to 7:30. No registration is necessary for this in-person event.

 

 

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