Lawinenlagebericht

Seeley Lake

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

Dangerous avalanche conditions exist. Wind slabs will continue to grow in size and distribution today. Expect to find thicker and more hazardous slabs at higher elevations.  Be alert to changing conditions and pay close attention to blowing snow. Avoid wind-loaded slopes greater than 35º. It may still be possible to trigger a sizeable persistent slab avalanche in the Southern Bitterroot. We recommend avoiding travel on slopes steeper than 30° in this zone.  Triggered avalanches from flatter terrain below, above, and to the sides of steep slopes are possible. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2.5

    Plenty of snow remains available for wind transport, and the potential for dangerous wind slabs is growing.  Yesterday winds slabs were touchy on loaded northeast and cross-loaded southwest slopes in the Rattlesnake. Less wind was reported near Lolo and the Central Bitterroot; however, winds likely have and will continue to load slopes. Expect moderate west winds with strong gusts for the Missions, Seeley Lake zone, Rattlesnake, and Central Bitterroot today. The southern Bitterroot will have light southwest winds with strong gusts.

    Be alert to changing conditions as you climb into the upper elevations, where stronger winds will build thicker slabs large enough to bury and injure you. Signs that wind slabs have formed include cornices above the slope, hollow-sounding pillows of drifted snow, and shooting cracks. Avoid wind-loaded slopes greater than 35º. 

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–3

    We identified a layer of faceted snow resting atop the hard basal crusts from early December above 7,500 feet in the southern Bitterroot. Column tests found propagation on this layer on December 17th.  It is now buried approximately 4 feet deep. As this layer gets buried deeper, the likelihood of triggering a slide decreases. However, the consequences of a slide have increased. A slide on this layer would be very large and destructive. It’s best to avoid travel on slopes steeper than 30° until further investigation of this layer rules out the possibility of triggering. It’s possible to trigger avalanches from flatter terrain below, above, and to the sides of steep slopes in the Southern Bitterroot. 

Avalanche Discussion

A storm brought widespread light to moderate snowfall over the last 24 hours. Temperatures have stayed mild, with denser snow falling below 6,000 feet.  Snowfall amounts vary across the forecast area, and loading has occurred throughout. Higher elevations have received the most significant snowfall and wind and deserve attention.  Accumulations in the 10 to 14-inch range fell since Sunday with snow levels near 3,000 feet. 

The main storm will move south and eventually out of the forecast area this morning. Lingering snow showers at higher elevations are likely. It will take time for the snowpack to adjust to the recent rapid loading. 

The following system will arrive tomorrow with increasing southwest winds to 20-25 mph with gusts 30-35 mph at the highest elevations. Strong winds and snowfall is expected Thursday as well. Accumulations in the 12-inch range are possible with this system. Snow will continue into the weekend.

We have yet to find layers of concern, and instabilities have been isolated to the surface of most areas across the forecast zone. However, these surface instabilities have grown and will continue to grow larger, more dangerous, and widespread as wind loading and settlement continue. The exception is a layer of faceted snow identified near the snowpack base above 7,500 feet in the southern Bitterroot. For more information see observation from December 17th. 

The recent storm came in with substantial precipitation rates and rising temperatures.  Yesterday we noticed that the deposited snow was dense and much of it fell on top of previous low-density snow in the Rattlesnake. This was not observed in Lolo and the central Bitterroot.  The extent of storm slab activity has likely decreased. However, it's a good idea to watch for lingering storm slabs. Be especially mindful if you plan to travel on slopes steeper than 40 degrees.

Many thanks to the folks who have been submitting observations. They are extremely helpful for assessing conditions throughout the forecast area. Please continue to submit them here:

https://missoulaavalanche.org/submit-an-observation/

Ski and ride safe.

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