Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
3 · Erheblich
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Kernpunkte

Human triggered and natural avalanches will be likely today. Avalanches have potential to step down or break on buried persistent weak layers, creating very large avalanches 4-6 feet deep.

Keep it simple today. There are multiple overlapping avalanche problems, all of which are capable of producing an avalanche large enough to bury you. Avoid the avalanche problems by sticking to slopes under 30 degrees that are not connected to or underneath steeper slopes.  Even small slopes can bury you if they bring you into creek bottoms, road cuts, or other terrain traps. 

Avalanche danger is highest along the Bitterroot Crest where 3-5 feet of snow has fallen with more expected today. 

The Considerable danger at low elevation is specific to Lolo Pass. Elsewhere at low elevation where the new snow is falling on dirt, avalanche danger is Moderate with the primary concern being larger avalanches running from above into low elevation terrain. 

Lawinenprobleme

  • Wind Slabs

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

    Moderate to strong transport winds continued to blow last night, although nothing like the gale force winds experienced yesterday. 

    We have had 48 hours of heavy snowfall and consistent wind to blow snow around and build overlapping slabs. With another foot or more of new snow today, these older wind slabs will be buried or hidden by new slabs. Add in variability in wind speeds and we can expect loading to occur in areas not previously wind loaded. 

    With 60mph wind speeds like yesterday, be alert for unusual wind loading locations. Expect to see wind slab lower on the slope than you normally would, or to see usually sheltered terrain with wind slab as the strong wind reaches into sheltered terrain. 

    Natural avalanches through cornice failure are likely today. Wind slabs in areas with a connected start zone now have enough snow to reach D3 in size. 

    Wind slabs can be identified by their smooth or rounded appearance. Watch for shooting cracks, whumfing, and fresh avalanches. 

    Slope angle will be the only way to manage the wind slab problem. Avalanches are unlikely on slopes under 30 degrees in slope angle. Avoid low angle terrain with steeper avalanche terrain above as avalanches could be remotely triggered or fail naturally. Do not travel underneath cornice unless absolutely necessary. 

     

    (3/12/2026)

    Example of freshly loaded slope with wind and new snow. Note the smooth or pillow like appearance of the windblown snow. 

    Photo: Cam Mackenzie

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    Storm snow totals are hard to lock down right now, but expect to encounter 2-4 feet of fresh snow. Yesterday afternoon was warmer than expected, followed by a cool down last night. As today warms up, we can expect another density inversion (heavy snow over lighter snow) within the storm snow. With that, expect the storm snow to be reactive to skiers and riders. 

    Common places to trigger a storm slab are convex rollovers and at the base of cliffs. Use things like test slopes to see how reactive and “slabby” the new snow is in your area. While storm slab is often a manageable problem through things like ski cuts, we are approaching (or already at) the point where the risk/reward for this strategy is too risky. 

    With the problem overlap with wind slab, there is no definitive line between storm slab and wind slab. Especially with the strong wind reaching into sheltered terrain yesterday, storm slabs could have a layer of more stout windblown snow within the storm slab. 

    Be careful of the trap with this problem where there is too much new snow to ski or keep momentum on 30 degree slopes so you naturally seek out something a bit steeper and unintentionally end up on a 35 degree slope trying to keep momentum. If you do this, you are moving into avalanche terrain where storms slabs D2 in size could be triggered.

    (3/12/2026)

    Dense 9-10% density snow on Thursday

    Photo: West Central Montana Avalanche Center

  • Persistent Slabs

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

    Multiple weak layers of buried surface hoar, buried near surface facets, and crust/facet layers were buried 1-3 feet deep at the start of this storm. By now, these layers are buried 3-5 feet deep with potential to be buried by a 4-6 feet slab of snow by the end of the day today. This is a serious load that will stress buried weak layers and likely fail naturally. 

    If these slopes have not yet failed and avalanched naturally during this storm, we are at the point where there is enough of a slab and connected start zone to produce avalanches D3+ in size. 

    Normally we would suggest digging in the snow to identify these layers. Today, with the other overlapping avalanche problems,  don't try to outsmart the problem. Terrain is the only management strategy. 

    Like the wind slab problem, low angle slopes free from overhead hazard are the only way to avoid this problem today. If you have to travel under large avalanche paths (Lost Horse Road), move one at a time and do not linger. Today is not the day to tempt fate or mess with this avalanche problem. If you are caught in one of these avalanches, it could be unsurvivable. 

Avalanche Discussion

Spring storms and atmospheric rivers have significant unknowns and challenges. Snow lines can vary or change dramatically. Temperature changes can change what was expected to be multiple feet of low density snow into a foot or less of very dense wet snow. Boundaries between warmer air and cooler air can shift. Yesterday, we saw a bit of everything when it comes to a springtime atmospheric river. 

Like yesterday, while there is a lot going on with this storm, it is also simple. This is not the time to mess with avalanche terrain. 

SNOTEL sites are not capturing the new snow totals accurately. If we work with SWE (snow water equivalent) here are the storm numbers since March 11 so far. 

  • North Fork Jocko: 1.1 inches SWE
  • Stuart: 2.4 inches SWE
  • Lolo Pass: 2.3 inches SWE
  • Twin Lakes: 4.6 inches SWE
  • Saddle Mountain: 3.3 inches SWE

If we take these snow water equivalent numbers and approximate based on atmospheric temperatures, there is likely multiple feet of snow in these locations. Yesterday, we visited Lost Trail Pass and Lolo Pass to manually compare measurements to SNOTELs and in both locations found 2-3 feet of fresh snow. 

Let us know how much snow you find today. Even something as simple as saying “I was at Lake Dinah and found 1.5 feet of dense new snow” is extremely useful for us. 

What will happen today? The biggest variable today is where the boundary between the warm atmospheric river and a cooler arctic front will set up. Above this boundary, expect cooler temps and low density snow. South of the boundary, expect warmer temps and wetter snow. 

With this much uncertainty in conditions, a conservative approach is necessary. It is likely today will be another day without great visibility to see how widespread the avalanche cycle is. There is good news, problems like storms slab and wind slab can settle out within days. In the meantime, there will be great skiing and riding on lower angle slopes today. 

Please submit an observation to let us know what you see in the mountains today. It can be as simple as letting us know how much new snow fell in your area. Every bit of information helps, especially during large storm events.

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