Bollettino valanghe

Flathead Range & Glacier NP

Flathead Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Open full map
Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The return of southwest winds and warming temperatures increase the chance you could trigger a slide where the wind has formed drifts or stiffened the snow surface. Avoid the exposed wind-hammered slopes for softer and safer snow in sheltered terrain.

Problemi valanghivi

  • Wind Slabs

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

    Yesterday, observers reported blowing and drifting snow from southwest winds and remotely triggered cornices. Moderate to strong winds overnight and throughout today continue to thicken recently formed slabs on typical leeward aspects. Today's light snow will add to the moderate amount of snow that is available for transport. Warming temperatures will aid in the formation of fresh slabs.

    Look for blowing snow as you gain elevation to identify where slabs form. These features will be most developed near and below ridgelines and saddles, around prominent terrain features, and in cross-loaded gullies. Fresh slabs will be thin, relatively soft, and may crack beneath you. Shooting cracks signify an unstable slab directing you to a sheltered aspect or a lower-angle slope. 

    ADDITIONAL DISCUSSION: Arctic winds from the north and east left a patchwork of slabs in unusual locations Tuesday through Friday. These features are found on atypical aspects at all elevations and are hard, thick, and supportable to a rider's or snowmachine's weight. Instead of cracking beneath you, they will fracture above you and wider than anticipated. They may sound hollow, like a drum. You don't want to mess with these beasts, so give them a wide berth, as their riding quality is lousy anyway. 

    (2/25/2023)

    A soft slab avalanche on a wind-loaded convexity. This is on a north-east facing slope at 5200'.

    Photo: md

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Numerous large to very large avalanches failed this past week on buried weak layers. Getting tangled up in many of those would have been unsurvivable. Most slides occurred on leeward aspects at mid and upper elevations where the weak layers are most developed.

    These layers are generally buried deeply in our pack following this week's snowfall. However, today's warming temperatures may increase their sensitivity. Digging down to see if these layers are present is a chore, and typical snowpack tests may not be effective in testing their strength. Default to safer terrain until we can remove this problem from the list. Choose lower-angle slopes free of overhead hazards. Steer around convexities and thin windswept or rocky areas where your weight is most likely to impact these layers.

    (2/25/2023)

    A very large hard slab avalanche on a wind-loaded slope.

Avalanche Discussion

Frigid temperatures associated with the Arctic air mass began to moderate Friday and reached a comfortable level by Saturday. Ambient air temperatures climbed to and above freezing on the valley floors, in the mid to upper 20s at middle elevations and upper teens at upper elevations. Readings this morning are approximately 50 F warmer than this time 48 hours ago! The snowpack does not like rapid change, and we are concerned about how the snow surface will react to these relatively balmy temperatures. Warming temperatures can initiate the development of surface slabs and affect layers deeper in the pack. 

Yesterday's clearing skies gave observers great views of recent avalanche activity during the Atmospheric River on February 20 and 21. There were numerous crowns in the Middle Fork, where 6 of the 7 submitted observations originated. Most of the activity appears to have occurred on slopes loaded by southwest winds at mid and upper elevations. So far, we have seen a mix of soft slabs involving new and wind-blown snow and plenty of large to very large hard slabs that failed on buried weak layers. If you get out and about and see any interesting slides over the next few days, please share a few photos with us. Thanks!

Southwest winds returned Friday afternoon and have been busy building fresh slabs and cornices on typical leeward aspects, NW-NE-SE. An observer in John F. Stevens Canyon remotely triggered a fresh cornice just from standing 5 feet away. New slabs and cornices may be developing on a hard surface scoured recently by northeast winds. If so, these wind features may be more reactive to a rider's weight than usual.

Observers report many aspects at mid and upper elevations hammered by the wind. An experienced backcountry user noted, "most terrain, regardless of aspect, was severely wind affected. " This is reason enough to direct you to sheltered locations, allowing you to enjoy soft snow and a safer experience. 

 

 

 

Regioni coperte