Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Avalanche danger will reach considerable by mid day today as a strong storm arrives with new snow and strong winds.

Human triggered avalanches are likely, especially in wind loaded terrain along ridgelines and at upper elevation. There is also the possibility of triggering a larger persistent slab avalanche.

Be aware of what is above you, as you could remotely trigger an avalanche today from above, below, or to the side of steeper slopes. 

If you see cracking, collapsing, or poor snowpack structure in a snowpit, stick to slopes under 30 degrees.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    New snow and strong winds will create fresh wind slabs at the upper elevation today, building on existing wind slabs from the past 24 hours. Expect any wind slab to be reactive today, with human triggered avalanches 12-24 inches deep likely. 

    Slabs will be deepest and most widespread on north through east aspects. In complex terrain like cirques or couloirs, shifting winds will be enough to create smaller wind slabs or cross loading on all aspects. In addition, high wind speeds, as we expect to see today, often cause wind slabs to be built lower on slopes than usual. Don’t rule out a mid-slope wind loaded pocket today. 

    Wind slabs can be recognized by their smooth, pillow-like appearance, but they may not always be obvious when new snow covers them. If you encounter cracking, collapsing, whumfing, or the snow has a hollow slab-like feel to it, step back to terrain under 30 degrees.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Multiple persistent weak layers of near surface facets, buried surface hoar, and isolated depth hoar on upper elevation north aspects exist in the snowpack. Until now, these layers have not been problematic as they have had no slab above them. This is likely to change today with the incoming snow. 

    It will be possible to trigger a larger avalanche, potentially breaking near the ground and taking out the entire season's snowpack today. 

    Snowpits can be a useful tool for identifying areas with buried persistent weak layers, but don’t let a lack of unstable results in your snowpit tests justify jumping into avalanche terrain with poor snowpack structure.

    Collapses and whumfing are signs that the persistent weak layers are becoming reactive and fractures are propagating. If you encounter these red flags, stick to slopes under 30 degrees and do not linger underneath avalanche terrain. 

    Today will be the first significant load these weak layers have seen all season. The best management strategy today is avoidance and giving the snowpack time to adjust or avalanche naturally.

Avalanche Discussion

It took a while, but winter is finally here in force. A strong winter storm impacts all three forecast areas today, bringing new snow and high wind speeds. Snow totals will be highest in the central and southern Bitterroot, with new snow totals today of a foot or more. Storm totals decrease moving north, but areas of the Rattlesnake and Seeley zones could still see 5-7 inches of new snow today. Winds today will be out of the southwest in the 30s, with gusts into the 50s. 

Since the start of the storm on January 7th through today at 0500, storm totals are as follows :

Seeley North Fork Jocko-  10” of new snow with .9” SWE (snow water equivalent)

Rattlesnake Stuart- 4” of new snow with .2” SWE

Central Bitterroot Twin Lakes - 6” of new snow with .4” SWE

This storm will be the first significant load on our weak snowpack. For the past few weeks, the message has been that we have multiple persistent weak layers in the snowpack but no associated avalanche danger. That has changed. By mid day today, we will have a slab across all forecast zones on top of existing weak snow. All that is missing now for an avalanche is a trigger. Keep your powder fever in check today, and don’t be the trigger to complete the avalanche triangle of a weak layer, a slab, and a trigger. There will be excellent skiing and riding on low angle slopes today outside of avalanche terrain. 

Avalanche danger today exists primarily on the north and east aspects, especially in wind loaded areas. Most south facing aspects have a very stout crust on the surface. Although not a primary avalanche problem today, slough management in loose dry snow will be important where new snow sits on crusts. Sloughs can run faster and further than expected on such stout crusts. 

Hazard will continue to rise through the week as a series of storms impacts our area.  Bitter cold temperatures could complicate even a small injury in the backcountry this week.

This storm will certainly help with conditions, but remember that our snowpack is still thin. Hazards such as buried stumps, logs, and rocks are widespread and may be concealed under fresh snow. 

Please consider submitting an observation of what you see in the mountains. Even a simple photo helps forecasters better understand conditions and create more accurate forecasts.

Contact us here if you're interested in volunteering for a field day with the Avalanche Center. This is a unique opportunity to ski or ride with a forecaster and learn or grow your own snow and avalanche skills. 

Ski and ride safe!

 

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