Lawinenlagebericht

Flathead Range & Glacier NP

Flathead Avalanche Center
Auf der Karte ansehen

Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
Open full map
Veraltet — dieser Lagebericht ist last year abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Fresh slabs of wind-drifted snow will thicken throughout the day and could be reactive to the weight of a rider. Warming temperatures and filtered sun may develop wet snow avalanches in the dry surface snow. You can still trigger a large avalanche involving buried weak layers on slopes without a supportable crust. Monitor changes in the snow surface and default to lower-angle terrain.

Lawinenprobleme

  • Wind Slabs

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

    Moderate to strong south-southwest winds continue transporting the 5-10 inches of snowfall from earlier in the week. Some of this snow is sublimating from the elevated wind speeds, while the rest forms thin slabs on leeward slopes.  These features will be thicker and more widespread in locations where the most snow fell. Due to the impressive speeds, slabs may be further downslope than expected. Look for them near and below ridgelines, in mid-slope cross-loaded gullies, and behind terrain features like rock outcroppings and trees.

    Active wind transport throughout the day should make it easy to identify where these form. Fresh cornices may be sensitive and point in the direction of wind deposition. Cracking in the surface indicates you have found an unstable slab, directing you to a lower-angle slope.

    Surface slides have the potential to trigger a hard slab avlanche, as described in our Persistent Slab problem.

    (2/24/2025)

    This image shows active wind transport that should be expected throughout the day. Slabs of wind-drifted snow will form on the downwind sides of ridgelines and in cross-loaded gullies.

    Photo: Mark Dundas

  • Loose Wet

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

    Mountain temperatures minimally cooled overnight and may climb above freezing this morning. Sun filtering through the partly cloudy skies could warm and moisten dry surface snow on solar aspects. Natural wet loose avalanches may develop during sustained periods of direct sun, particularly in steep, rocky terrain sheltered from the wind. Dry snow on shady aspects may warm for the first time. If so, a natural wet cycle can potentially entrain more snow and produce larger slides than on sunny slopes. 

    Monitor the relatively dry surface snow to see if it becomes moist. Rollerballs and snow glopping onto your machine or boards indicate the snow is warming, and wet loose slides may follow. If you notice this change, move to a shadier aspect or a lower angle slope. Limit your time spent above terrain traps where the snow can pile up deep.

    During last weekend’s heat wave, loose slides triggered large avalanches on buried weak layers. If wet loose slides develop on shady slopes, there is the chance they could initiate a destructive hard slab avalanche, as described in our Persistent Slab problem.

    (3/7/2025)

    Wet loose activity during the current warming has been mainly confined to steep, rocky slopes facing the sun. With today's increasing temperatures, these may become more widespread. 

    Photo: Rob Millspaugh

  • Persistent Slabs

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

    January’s weak layers (sugary facets, surface hoar, or facets + crusts) rest beneath a 2-3 foot thick slab deposited in February. You can trigger a large avalanche where these weak layers are preserved and susceptible to the weight of a rider. The most likely locations are on steep shaded slopes that did not slide during the February Atmospheric River and last weekend’s heat wave. Solar aspects are generally capped with a stout, supportable crust that limits your ability to impact the weak layer. Although less likely, you could trigger slides on these slopes if the crust breaks down or is nonexistent. 

    The chance of triggering a slide increases in wind-affected terrain where the slab depth is variable and the weak layer is closer to the surface. Before triggering an avalanche, you may not experience noticeable signs of instability like snowpack cracking and collapsing.

    Persistent Slabs can break much wider than expected and in surprising ways. Surface slides or cornice fall could result in a large slab avalanche.

    Digging into the snow is the only way to identify if your slope contains this layer. Choosing lower-angle terrain not connected to steep slopes is the easiest way to mitigate this problem.

Avalanche Discussion

Today (Sunday) is the last day of the current warming trend, which has, so far, produced limited wet snow avalanche activity. Saturday's cloud cover limited solar radiation, with WMR ski patrol and several observations reporting that the snow did not soften on solar aspects until late day.  The moderate to strong wind kept exposed slopes frozen and developed fresh slabs of wind-drifted snow. Many stations reported gale-force gusts over the past 24 hours. These features will continue to grow throughout the day as winds remain elevated. Their size will be limited by the relatively small amount of snow available for transport in many locations.

This morning's temperatures are warmer than the past few mornings, with readings just below freezing at mid-elevations. Despite the expected partly to mostly cloudy conditions, we anticipate temperatures to climb above freezing at all mountain stations. The 5-10 inches of snowfall from earlier in the week may sluff on steep slopes receiving direct sun. Our uncertainty is whether today's partly cloudy conditions will develop a greenhouse effect, allowing for the warming of the surface snow on shaded aspects.  Dry snow remains on any slope shaded from the sun, with a significant amount of surface snow available for entrainment.   

Glide avalanches remain on our radar during this weekend's weak thaw.  Glide cracks are found in all aspects at mid and upper elevations but are concentrated in sunny, mid-elevations. These features are notoriously hard to predict and can fail without warning. Continue to mitigate this problem by avoiding slopes with glide cracks.

Large seasonal cornices are found along many ridgelines throughout the forecast area. Warming temperatures make them sag and fail, possibly triggering a much larger slab avalanche on the slopes below. Limit your time spent below these features, and while traveling ridgelines, keep further back from their edge than you think is necessary.   

We are saddened to report that the recent heli-skiing incident in Alaska took the life of a member of the Flathead backcountry community. Charlie Eppard was a loving father, devoted husband, and long-time supporter of FAC and FOFAC. You can support his wife, Brittany, and their young daughter at this Go Fund Me account. An article in the Daily Interlake detailing this tragedy can be found here. 

Abgedeckte Regionen