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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Veraltet — dieser Lagebericht ist 2 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Triggering a 2-4 foot thick avalanche on a buried weak layer remains possible in the Flathead Range and Glacier Park. You will most likely affect this layer on shaded slopes harboring a shallow snowpack. Blustery conditions will continue forming thin slabs of wind-drifted snow that could be reactive to a rider's weight.  

 

Lawinenprobleme

  • Persistent Slabs

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

    In late February, an intense wind-loading event triggered multiple large to very large hard slab avalanches in the Flathead Range, central Glacier Park, and southern Glacier Park. All appeared to fail on a layer of weak, faceted snow 2-4 feet below the surface. This weak layer is best preserved and most problematic on shady slopes; however, in locations east of Essex, sunny aspects contain a mix of crusts and faceted layers capable of producing a destructive slide. The persistent slab problem is magnified in the mountains between Essex and Marias Pass, where the snowpack is generally thinner and weaker. 

    You're most likely to trigger one of these beasts in steep, rocky terrain similar to the photo to the right/below. Signs of instability, such as cracking or collapsing, may not be present before the slope you are on slides. Choosing lower-angle terrain without convexities is the easiest way to manage this problem. 

    (3/9/2024) This is a hard slab avalanche on a northeast aspect at ~7,000 feet on a sub-ridge of Great Northern Mountain. It remains possible for riders to trigger a slide similar to this today. Photo: Ernesta McIntosh

  • Wind Slabs

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

    Southwest winds increased on Saturday and will stay elevated into Monday morning. As riders noted yesterday, plenty of dry snow from last week's storms remains available for transport, with more on the way later today. As you gain elevation, you will find thicker and larger slabs downwind of ridgelines and saddles and on the sidewalls of gullies.

    Today's blowing snow and cornice formation point toward slopes with developing slabs. Look for clues that the wind has been at work, such as drifts, dunes, rippled snow surfaces, and snow pillows. Cracks shooting away from your boards or machine indicate you have found an unstable slab directing you to sheltered or lower-angle terrain. 

    (3/9/2024)

    The fracture line of a skier-triggered avalanche in the southern Whitefish Range was reported on March 4th. Slabs of wind-drifted snow were built Saturday and will continue thickening today. These may be reactive to a rider's weight. 

    Photo: Sarah Williams

Avalanche Discussion

Yesterday (Saturday), temperatures reached 40F+ at many mid-elevation weather stations and 50F+ at low-elevations. Despite the mild conditions, high clouds and breezy conditions mostly kept the wet loose problem in check. One party did report triggering a small wet slide near the bottom of the Skook Chutes, while another noted rollerballs (photo). With cooler temperatures on tap for today, we have removed this problem from the list. However, you could probably trigger a small wet loose at low elevations where the temperature has remained above freezing since late morning yesterday. 

Winds increased yesterday afternoon, and last week's snow began transporting (photo). Winds cranked up overnight with a gust of 92 at Tunnel Ridge and into the 50s in several other locations. An approaching cold front will elevate the wind speeds and bring snow to help fuel the wind slab problem.

Sarah and Rob visited the site of two skier-triggered slides in the Chicken Bones area east of WMR from March 4 and 6. These occurred in an area cross-loaded by last week's strong winds and appeared to fail on a faceted weak layer below a melt-freeze crust 21 cm from the surface. 

In the Whitefish Range, several slides failed on buried weak layers last week (photo) and are clustered in a small area on the southeast side of this zone at mid-elevations. The crowns seem thinner than slides in the Flathead Range, so Jeff and Sarah will investigate one of these today and try to solve this puzzle.

The Flathead Range, interior Glacier Park, and southern Glacier Park are the epicenters of large-to-very-large avalanche activity. Good visibility allowed for more observations of crowns in this area yesterday (photo, photo).

A huge thank you to the 10 parties that submitted observations yesterday (Saturday). Riders found dry snow on shaded aspects and decent riding conditions on sunny aspects at mid and upper elevations, with generally stable snowpack tests noted by The Patrol Fund Level 1 class (observation, observation).

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