Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Below freezing temperatures have allowed for a respite from the recent wet snow hazards. The danger is LOW this morning but will rise later today into Monday as fresh snow and wind return to the Flathead. Expect thin slabs to increase in thickness as you gain elevation, particularly on leeward slopes. Despite the arrival of spring, buried weak layers that formed earlier in the winter are a great reminder to choose slopes 35 degrees or less, particularly in areas not harboring a stout surface crust.   

Lawinenprobleme

  • Wind Slabs

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

    After a lengthy drought, precipitation has come back home with Friday and Saturday's light snowfall, a taste of what is on tap for the next few days. You won't see much new snow or associated avalanche problems during today's daylight hours. Still, we expect the danger to rise as a developing storm enters our area later today and overnight. Thin slabs will increase in thickness as you gain elevation, particularly on leeward slopes. Slabs will be most sensitive to a rider's weight where they form on top of a slippery surface crust. Cracking in the surface snow (remember that?) is a sign of instability. Terrain sheltered from the wind will generally be a safer location to ride. 

    (3/10/2021) Thin recently formed wind slabs failed easily on several inches of faceted snow.

  • Persistent Slabs

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

    Temperatures at mid and upper-elevation weather stations dipped below freezing for the past 24 to 48 hours. A surface crust is developing on sunny aspects and on those northerly slopes which recently got wet for the first time. Cloudy, cool conditions have put a halt to the recent fun of riding corn but, on the plus side, have limited the amount riders can affect weak layers buried 2 to 6 feet below the surface. Areas harboring a stout surface crust are generally safer than slopes with a thin or non-existent crust. Continue to steer around windswept slopes or those with a peppered rocky appearance where the weak layers are closer to the surface. Choosing terrain 35 degrees or less in steepness is still the go-to as we navigate this unusual Persistent Slab problem.

    (3/16/2021) A hard slab of snow sitting over buried persistent weak layers.

Avalanche Discussion

March came in like a lamb and looks on track to exit like a lion, or at least a lion cub. Following nearly three weeks of well below-average precipitation, forecasted unsettled weather should affect the Flathead for most of this coming work week. Since Friday, area weather stations have only recorded light snowfall, with Noisy Basin in the Swan Range favored. That should begin to change later today as a more robust system moves into the area.

This past Friday, we listed a new snow avalanche problem, wind slab, for the first time since the last week of February. You may remember that storm resulted in bountiful SWE totals, including 3.8” at Flattop. Those were the days. We’ve endured eighteen consecutive days of combining one or more of the following problems: wet loose, cornice, glide, and persistent slab. The snow depth at Snotel stations dropped a foot or more in central Glacier Park and the Swan Range, with only a paltry SWE increase during this period. Yikes, not the La Nina March of our dreams.

Hopefully, this week’s precipitation results in avalanche problems associated with freshly fallen dry snow, such as storm slab, wind slab, and dry loose. Most of us would welcome a fresh round of powder to take the place of recent wet problems, which have worn out their welcome. Regardless, we’re still stuck with the old snow problems related to buried weak layers above the January 13 crust. With cool temperatures forecasted, we expect southerly slopes to continue developing a thick stout crust. The crust will minimize the effect riders have on buried weak layers and allow us to trim the distribution of the Persistent Slab problem. With recent observations few and far between, we need a bit more information before taking this step.

Due to the recent and forecasted cool and cloudy weather, we removed Glide avalanche from our problems list. You may remember that we had a bounty of glide cracks and glide avalanches during the recent heatwave. Numerous glide cracks exist across our area on northeast through southeast through southwest slopes at mid and upper elevations. When the warm sunny weather returns, Glide avalanches will return to our problem list. We continue to recommend not recreating on or below slopes harboring glide cracks.

Did you know that we create a weekly snowpack update and weekend outlook video each Friday? You can view it in the media gallery below or here.

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