Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

You can trigger an avalanche large enough to bury you on shady slopes. Warm temperatures overnight and today may increase the chance of wet snow avalanches. If you are sinking into mushy snow, choose lower-angled terrain to reduce your risk. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    You could trigger a 1-2 foot thick avalanche on a layer of weak snow buried beneath last weekend's storm snow. The weak snow is thickest and best preserved on shady aspects at mid and upper elevations. Natural and human-triggered avalanches failed on this faceted layer last Sunday, but we have not received reports of any avalanche activity since then. However, recent warming may consolidate the surface snow into a slab in areas previously unconsolidated. 

    Warning signs such as collapsing or whumphing are becoming less common. The chance of remotely triggering one of these slides is decreasing. You may not receive a warning sign until the slope you are on avalanches. This problem is near the surface and can be found by digging beneath last weekend's snow and testing this layer. Default to lower-angle terrain for a safer experience.

     

     

    (4/2/2023)

    Slide was triggered from a 32 degree ridgeline. The slab propagated roughly 600 feet and wrapped into two separate drainages. 

    Photo: Cam

  • Loose Wet

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

    Yesterday, temperatures climbed well-above freezing at all mid and several upper-elevation weather stations. Field observations are limited, but we assume slopes receiving sustained sunshine experienced a Wet Loose avalanche cycle as last weekend's surface snow warmed. Slides were larger and more dangerous in the Flathead Range and southern Glacier Park, which benefited the most from the recent snowfall. 

    Temperatures this morning are warm, with readings on either side of freezing at mid and upper elevations. The overnight refreezing of the snow surface was poor, and we expect only a thin, unsupportable surface crust in many locations. As temperatures warm, this crust should break down quickly, allowing you to sink into the mushy snow beneath and increase the chance that you could trigger a wet loose slide. Resulting slides may travel far on the underlying crust and could trigger a larger slide on a buried weak layer. Upper-elevation locations exposed to south-southwest winds may remain frozen. 

    We are unsure if yesterday's warming affected shady aspects. Today's temperatures will top yesterday's and may affect snow in shady aspects. Slopes warming for the first time will develop rollerballs, which are a precursor to a wet slide. Choose lower-angle slopes where you or your machine sink more than a few inches into the surface mush—limit time spent in long-running gullies or above terrain traps where the snow can pile up deep. 

    (12/28/2022)

    Dirty debris signifies that this slide ran on the ground removing the seasonal snow cover. This slide looks to be a wet loose. However, there may be a crown at the top of the slide.

    Photo: Mark Dundas

Avalanche Discussion

Spring temperatures have finally arrived in the Flathead following an unusually cool winter and early spring. Yesterday, Stahl Peak (6030'), Noisy Basin (6040'), and Flattop (6300') reached the low 40's F with upper elevation stations at WMR and Tunnel Ridge climbing to the upper-30s. As of 0400 this morning, temperatures remain at or above freezing at many mid-elevation stations. Today will be cloudier than yesterday, but we can expect temperatures to be 5-8 degrees warmer.

Wet loose activity in March was limited by consistently cold overnight temperatures, which minimized their size and distribution. Today, instabilities will develop quickly as the thin eggshell-like surface crust breaks down as the day heats up. We expect shady aspects to warm and moisten at mid-elevations and possibly at uppers. Wet slides have the potential to gouge deeper into the snowpack as they descend in elevation.

Warm weather increases the potential for cornice fall and glide avalanches. Forecasting for either of these is difficult and imprecise, and we recommend safe travel protocols to limit getting tangled up with either of these beasts. While traveling ridgelines remain well back from what appears to be the edge, as these impressive wind features are often overhanging. Limit your time spent on slopes beneath these, as a large cornice fall can trigger a large avalanche on the slope below. Glide cracks can fail catastrophically or melt in place. During periods of extended warming, avoid being on slopes where the seasonal snowpack is gliding downhill.

Have feedback for us? Let us know how we can serve you better. Special thanks to Friends of FAC for creating this survey: link here.

FAC will issue daily forecasts through Easter Sunday, April 9. Following this, we will give snowpack updates several times a week through April as conditions dictate. 

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