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

You could trigger an avalanche in mushy snow as the day heats up. Warm temperatures and sunshine may initiate slides at upper elevations. Choose lower-angle slopes or stay ahead of the sun for a safer experience. Yesterday's large triggered avalanche proves that buried weak layers are still a concern.

Problemi valanghivi

  • Loose Wet

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

    Today is the final day of an extended run of warm and sunny conditions responsible for the Wet Loose problem. Fortunately, modest daytime highs and well below-freezing readings overnight have limited the extent of avalanche activity. However, temperatures have slowly climbed over the past few days resulting in the surface crust on solar aspects breaking down earlier, with warming beginning to affect the snow surface on the northern side of the compass. 

     The crust thins with elevation and is found on sunny slopes up to 7000 feet or higher. As the crust deteriorates through the day, the danger will rise. With today's warming temperatures, recycled powder on shady slopes may be susceptible to developing wet snow instabilities.

    The natural Wet Loose avalanche activity on sunny slopes below 7000 feet is diminishing, but today's warming may initiate slides above this elevation. Triggering a slide in mushy surface snow remains likely as the day heats up. A crust that cannot support you or your machine indicates instability. Rollerballs and pinwheels are precursors to a wet slide. 

    Stay ahead of the sun today, or select lower-angle slopes to enjoy the corn-like conditions. Choose a route that does not expose you to steep overhead westerly aspects on your exit. Limit time above terrain traps where even a small slide can pile up deep. Northerly aspects should remain safer and hold higher-quality snow.

     

    (1/8/2023)

    Small rollerballs due to the warming of the surface snow.

  • Persistent Slabs

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

    Several weak layers capable of producing a large destructive avalanche can be found throughout our snowpack.

    • Faceted snow formed in November near the bottom of the pack is responsible for the recent snowmobile-triggered slide in the northern Whitefish Range and the natural slide on Elk Mountain earlier this week (Photo above/to the right).
    • Faceted snow resting on the Christmas crust.
    • Over the past two months, a weak layer and crust combination from mid-January has been responsible for most of the Persistent Slab avalanches. This layer is generally found 2-4 feet below the surface.

    The Persistent Slab has become a low-likelihood high-consequence problem. With relatively deep snow depths across the area, these layers are generally buried at a depth that a rider is unlikely to affect. However, as recent avalanches signify, thin areas in the snowpack are likely trigger points. These include rocky outcroppings and wind-swept or scoured locations where the weak layer is closer to the surface.

    Riders on the east side of Glacier noted a hard slab avalanche that failed during their ascent yesterday. Mountain goats may have triggered this slide.

    Terrain selection is the most straightforward way to deal with this issue. Choose slopes with a deep, uniform snowpack without a peppered rocky appearance. When in doubt, defaulting to lower-angle slopes is the best choice.

    (3/17/2023)

    The crown is thickest in the center and tapers to both edges. We believe the avalanche initiated in the rocks on the lookers' right.

    Photo: md

Avalanche Discussion

Spring-like weather continues today before cooler and moist weather returns Monday and into at least the middle of the week.  Unfortunately, we find ourselves in a split flow, with most of the moisture staying south of our area and continuing to build upon the near-record snowpack in the Sierra Nevada Mountains of California. 

This is the fourth and final day of our current wet snow instabilities. Daytime and overnight temperatures have climbed slightly each of the past four days. We have bumped the danger rating to MODERATE at upper elevations to account for this warming. 

Yesterday, a group of riders was surprised by a hard slab avalanche that occurred during their ascent of Red Crow Mountain (7800') near Firebrand Pass just east of Marias Pass. The crown was 2-3 feet thick and 500 feet wide, with the debris traveling 800 feet. Interestingly, mountain goats may have triggered this slide as the party saw goats on the summit and found their prints on the summit ridge, and saw the tracks cross the bed surface.  These folks felt fortunate for their timing and had considered that slope generally benign and discussed using some of it for their approach. We sincerely thank this group for sharing this information in the interest of public safety.

The BNSF avalanche safety team was in John F. Stevens Canyon, where they did not notice any instabilities (Observation) An experienced rider visited the Middle Fork and found several cm of new snow on top of the crust on more northerly/sheltered aspects. Any sort of direct sun resulted in near-instant glopping. They observed a couple of glide cracks opening on solar aspects in Glacier and a handful of point releases on Mt Grant (Observation).

I toured the Autumn Creek trail just west of Marias Pass to document avalanche activity that had affected the trail. We noted three large crowns from the late-February avalanche cycle with two debris piles traveling long distances. I was in this neighborhood Friday and was surprised by the loose, dry snow on shaded low and mid-elevation slopes. Unfortunately, some of this snow had warmed and was sticky and glopping to skins by mid-day yesterday (Observation).

FOFAC Event: March 30th, 2023– Whether you're chasing tan lines, big lines, or both, you'll learn something valuable from FAC Lead Forecaster Mark Dundas about spring avalanche problems, how they differ from winter problems, and how to manage them. We will also discuss current conditions and concerns (or lack thereof!) with our spring snowpack. Enjoy a cold brew from Bias Brewing and a scoop from Sweet Peaks Ice Cream.

The event is free and open to everyone. Begins at 6 pm.

Regioni coperte