Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

 Increasing winds are drifting snow into slabs about 1 foot thick that may be reactive to the weight of a rider. Triggering an avalanche on a buried weak layer 1-2 feet deep remains a concern. The danger is most significant in locations facing NW-NE-SE. Sunny and windward aspects offer a generally safer experience. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Increasing southwest winds are drifting recent snow into slabs on leeward-facing terrain. Slabs will become thicker and more widespread as you gain elevation. An avalanche in the wind-drifted snow can step down to a buried weak layer resulting in a much larger slide. Look for blowing snow as you climb in elevation and note the density change in the snow you are traveling through to identify a slab. Cracking in the wind-drifted snow is a sign of instability, directing you to seek safer conditions in sheltered terrain.

    (1/1/2023)

    A well-developed cornice line from southwest winds cross-loading mid-elevations.

    Photo: Mark Dundas

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    The chance of a rider triggering an avalanche on a weak layer buried around 1-2 feet deep has increased in wind-loaded terrain. Buried surface hoar and facets can result in avalanches that may break wider than expected or higher on the slope above you. You may be able to trigger avalanches remotely—from gentler terrain below, above, and to the sides of steep slopes. Continue to dial back terrain choices in areas this layer exists, primarily NW-NE-SE at the mid and upper elevations. Slabs will be thicker and more dangerous as you climb in elevation. Choosing lower-angle terrain free of overhead hazards is wise until we can rule this problem out. There is limited evidence these weak layers exist in the windward and sunny aspects. On these aspects, utilize hand pits to identify the layer and assess the surface for the sign of a slab. 

    (1/20/2023)

    Checking the failure plane for buried surface hoar.  We found some!

Avalanche Discussion

A cold front entered the Flathead overnight, but precipitation associated with this feature has underperformed. Most mid-elevation weather stations received minimal accumulations overnight, with very light snowfall expected through the day today. Wind speeds associated with the front have been much lower than forecast, but there has been enough of an uptick to drive today's avalanche danger. Because of the discrepancy in recent precipitation totals and the distribution of weak layers, we continue to divide the avalanche forecast into two groups - team Swan Range and team everywhere else.

A huge shout-out to the stellar group of experienced riders who continue to submit observations on this website. We received nine comments from familiar faces Saturday, which helped immensely as FAC staff has had limited field time due to either illness or obligations instructing avalanche classes.

Swan Range: Wind speeds at the Aeneas Ridge (7186') weather station have averaged just below the threshold for snow transport over the past 24 hours. However, moderate to strong hourly gusts have been recorded during that same time frame, drifting snow into slabs on leeward aspects. This area has picked up 2-3 times more recent snow than the other zones, and we expect the fetches to provide plenty of snow for transport throughout the day. We have moved Wind Slab to Problem 1 in this range.

  • In the Swan Range yesterday, a rider experienced a collapse and shooting crack in the recent snow while third in line ascending a slope. The slope was steep enough to slide but it did not. This individual mentioned feeling humbled and unnerved. The photo of the crack was submitted with the on-point caption, "That means go away." Other observations from the Swan included less scary avalanche problems, such as Loose Dry sluffs on steep sunny mid-elevation aspects running several hundred feet. These sluffs were probably running on top of a crust formed during the January 13 warm-up. Anticipate triggering a sluff on very steep terrain today in aspects sheltered from the wind.

Whitefish Range, Flathead Range, southern Glacier Park: Wind speeds at the Snowslip (7000') weather station in the John F. Stevens corridor were sustained light with moderate to strong gusts over the past 24 hours. The Flathead Range does not have a working wind sensor. The Hornet station reports light winds with moderate gusts in the northern Whitefish Range, while the Link Mountain station remains rimed. Despite the relatively low wind speeds, we have moved the Wind Slab to problem 1 in both zones.

  • Riders in the central and northern Whitefish Range reported long-running sluffs in the 10-15 cm of loose surface snow on top of the 1-19 rime crust. Expect more of these sluffs to be triggered today in steep terrain. One rider side hilled short 40+ degree slopes and saw no signs of instability.
  • Observers in the Flathead Range also noted sluffing in the top 10-15 cm on top of a crust. Expect more of these sluffs to be triggered in steep terrain today. They found soft, drifted snow 8-10" thick on leeward slopes and leeward sides of gullies at upper elevations—no cracking or signs of sensitivity, but noticeable enough to affect their terrain choices.

Today's danger ratings: We have reasonable confidence in bumping the danger rating in the Swan to CONSIDERABLE at upper elevations or above 6500 feet. Higher wind speeds and more available snow for transport make this a relatively easy call. We are bumping the danger at mid-elevations, 5000-6500 feet, to MODERATE in the Whitefish Range, the Flathead Range, and southern Glacier Park. We are not confident that wind speeds at this elevation and the little snow available for transport will allow slabs of wind-drifted snow to form. The uncertainty of wind speeds in areas without working anemometers has led us to a slightly more conservative approach.

New video: Check out Cam's new video about the evolution of our snowpack in the media gallery below.

Education: Motorized Partner Rescue - Join us for an eight-hour field day on Saturday, January 28, 2023. More details are here.

Motorized Level 1 - Instructed by Eric Knoff and Six Points Avalanche Education from Tuesday, February 7, 2023, to Thursday, February 9, 2023. More details are here.

Regioni coperte