Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
4 · Gross
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Kernpunkte

We're letting the avalanche warning expire this morning. However, heavy snowfall, rain, and elevated temperatures continue to add weight and water, rapidly destabilizing our snowpack. Very dangerous avalanche conditions remain at all elevations and aspects. Large wet avalanches are very likely, leveling anything in their path. Storm slabs at upper elevations are likely, capable of running long distances and large enough to bury and kill a person. Persistent layers may reawaken and cause very large avalanches in the Central Bitterroot and possibly elsewhere. Avoid being on or under slopes steeper than 30 degrees. 

Lawinenprobleme

  • Wet Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    1–3

    Over 12 inches of new snow was received in the past 24 hours. Rain continues to fall, adding water and saturating the snowpack into a slab at elevations below approximately 7,500 feet. Water trickling through the snowpack may reach buried crusts and possibly trigger a wet slab avalanche. Like a thousand concrete trucks dumping their loads at once, when rain saturates the snow to beyond its holding capacity, wet avalanches will release gouging out and level anything in their path. Wet problems are hard to predict and can't be assessed with standard snowpack tests. Wet slides may run in areas not easily identified as avalanche terrain. Avoidance is our best option. Travel in avalanche terrain is not recommended. Stay well away from the base of slopes capable of sliding until it stops raining and temperatures cool back down.

    (2/09/2022) Example of wet avalanche from the Swan range. These will grow in size and consequence today.  Photo: Ryan Sorenson

  • Storm Slabs

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

    The storm arrived with a dose of heavy dense snow and rising snow levels, rapidly loading the snowpack. This quick change has deteriorated conditions and left heavy wet snow over less dense drier snow that can quickly form large destructive avalanches. Storm slabs are developing over various snow surfaces, including dry faceted snow and melt-freeze crusts. Strong southwest winds are also growing larger wind slabs on loaded slopes at higher elevations. Avalanches capable of running long distances and large enough to bury and kill a person are likely. 

    Avoid slopes over 30º and stay well away from the base of avalanche slopes.

    (3/1/2022)

    Example of storm slab avalanche from the Rattle Snake. Photo: Jeff Carty

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3.5

    Weak layers buried in the snowpack may reach their breaking point today as continued snow and rain add weight and moisture to the snowpack. Over the past week, we identified a crust/facet combo in the Central Bitterroot that likely became more reactive with the rapid temperature rise and snowfall we’re experiencing. Areas of the Gash and Bear creek have shown the most reactivity in recent observations however, the storm may reawaken dormant persistent layers outside of this.

    (2/23/2022) Facet crust combo identified 31 inches (80 cm) deep near Gash Knob. Photo: Todd Glew

Avalanche Discussion

Conditions continue to deteriorate as heavy wet snow and rain impact the forecast area. Red flags were waving yesterday, and we can expect them to continue to wave until we get a refreeze. It was snowing up to an inch yesterday morning. We observed natural storm slab avalanches failing on road cuts near Lolo pass. We noticed winds picking up out of the southwest. We also encountered wet, heavy snow over drier snow and cracking in the upper snowpack on test slopes. Less fresh precipitation was reported from the Rattlesnake. However, storm slabs were easily triggered on slopes over 35º. 

The storm came in with a warm and moist southwesterly flow that pushed across the Pacific Northwest, bringing precipitation and rising snow levels since Sunday night (02/27). Remote weather stations show a range of new snow totals.

  • Lolo Pass is winning the snow total game with 13” (2.0 SWE) since our last forecast and 8” (1.5 SWE) in the past 24 at 5,240 feet. 
  • The North Fork of the Jacko, Seeley-Swan region, 10” snow (1.60 SWE) with 5” (1.10 SWE) in 24 hours at 6,300 feet.
  • Stewart Mountain, Rattlesnake, 9” snow (1.90 SWE) with 6” (1.40 SWE) in 24 hours at 7,400 feet.  
  • Twin Lakes, Central Bitterroot, 10” snow (1.70 SWE) with 6” (0.90 SWE) in 24 hours at 6,400 feet.
  • Saddle Mountain, Southern Bitterroot, 12” (0.90 SWE) with 8” (0.70 SWE) in 24 hours at 7,900 feet. 

 Winds were light out of the southwest last night, with gusts to 32 mph on Point Six. Today we will have light to moderate winds in the morning tapering off in the afternoon. Snow levels are forecast to stay elevated in the 6,500 to 7,500-foot range, with the northern regions cooler (lower snow levels) and the southern regions warmer (higher snow levels). 

After a week of clearer skies and cold temperatures, widespread faceting has occurred in the upper portion of the snowpack. Strong and cold northeast winds followed by warmer productive westerly winds have scoured upper elevation slopes down to slick crusts, hard-packed wind board, and small isolated wind slabs prior to the storm. New crusts have also formed below approximately 6,500 feet on solar aspects and on all aspects below 5,500 feet due to elevated temperatures and sun this past weekend. 

Dangerous avalanche conditions exist across the mountains of West Central Montana. Choose low-angle and low consequence terrain far from the large runouts of avalanche paths if you venture out. 

Any observation on snow and avalanche conditions is very helpful to us. Even just a picture is great. Please submit observations here: https://missoulaavalanche.org/submit-an-observation/

Ski and ride safe.

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