Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
Voir sur la carte

Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The ongoing heatwave is limiting where you can recreate safely and enjoyably. Above freezing temperatures have left a mushy surface that will deteriorate further as the day progresses. Choose lower-angle terrain to limit your chance of triggering wet slides. Give weakening cornices a wide berth both on ridgelines and slopes below. The potential of a large hard slab avalanche on buried weak layers remains a concern until cooler weather returns.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Most mountain weather stations have recorded above-freezing temperatures for the past 48 hours.  Observers noted a wet loose avalanche cycle on southeast through west aspects at mid and upper elevations Friday. Expect natural avalanche activity to diminish on sunny slopes but increase on shaded aspects. Nevertheless, it will be easy to trigger surface slides anywhere the snow has become wet. Today is not the day to recreate on steep slopes! Choose lower-angle terrain free of cornices looming above. Avoid traveling above terrain traps where even a small slide can pile up deep.

    (4/2/2021) Wet loose slides occurred in surface snow from warming and solar input on steep southerly slopes on mid and upper-elevation slopes.

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    The blue whales of the backcountry loom above many leeward slopes, with the current heatwave weakening these enormous wind features. Calving cornices have the potential to trigger a slab of wind drifted snow at upper elevations. The worst-case scenario would be a large tumbling block initiating a destructive slide on buried weak layers. Stay far back from where you imagine their edge to be while traveling along ridgelines and choose slopes without this lingering overhead hazard.

    (3/30/2021) Recent westerly winds have regrown this cornice above the Shed 7 West path in John. F. Stevens Canyon.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    Warming temperatures increase the threat of triggering a weak layer buried 2 to 6 feet below the surface. The force of a van-sized piece of cornice tumbling down the slope could do the trick. You or your snowmachine may also be the trigger that awakens this lurking concern. To minimize your exposure to this problem, choose terrain 35 degrees in steepness or less that is consistent in slope shape top to bottom. Avoid areas with thin coverage such as a rocky peppered appearance or windswept look.

    (3/26/2021) The 1/13 crust found 28 inches below the surface on a SE aspect at 6300 feet. Two thin layers of facets sandwich this crust.

Avalanche Discussion

Dissapointingly warm temperatures overnight Thursday and Friday have prevented freezing the surface snow except for areas of the Whitefish Range which experienced a weak refreeze. Expect to find a thick layer of wet snow on the surface on many aspects and elevations this morning. With today's warm temperatures, this layer will deteriorate further through the day. The distribution of recent dry snow has diminished to a tiny area on upper elevation north aspects. This small piece of pie is expected to shrink with today's warmth further.  

Observations were scarce yesterday, but fortunately, we have a trusted, reliable observer in the Swan Range. He noted a widespread wet loose cycle at mid and upper elevation south and west slopes Friday. These slides were much more impressive than the previous day. Blase was at WMR and noted small D1 sluffs in the Skook chutes and found moist to sticky snow on northerly slopes. FOFAC board member Jenny Cloutier and I enjoyed a picnic in Rescue Creek while watching a wet loose cycle on mid and upper elevation south and southeast slopes. Most slides were relatively small, with perhaps one or two large enough to bury, injure, or kill a person. North aspects remained relatively quiet, with activity confined to rollerballs through our 2:00 p.m. exit. With sunny slopes becoming slightly worked over, we expect diminished natural activity on those aspects but increased activity on northerlies.

We are not listing glide cracks as a problem today, but they should be considered an elevated hazard until cooler weather rolls in Monday.  They are generally found on slopes facing southeast to the southwest to the west, although they have been spotted on other aspects. They may not be as obvious as they were a couple of weeks ago due to new snow and loose slide debris disguising their appearance. 

This past week's Weekly Summary and Weekend Outlook video is found in the media gallery and here.

Régions couvertes