Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Strong winds overnight and through the day will continue forming slabs on leeward aspects. Expect these to be reactive to a rider's weight and grow in size as the day progresses. Be alert for the danger of falling trees and branches from today's damaging winds. Warm temperatures continue to weaken the surface snow resulting in wet avalanches. Expect to encounter this problem on slopes not being cooled by the howling wind. To avoid triggering a dangerously large slab on buried weak layers requires choosing terrain less than 35 degrees where there isn't a stout surface crust under the recent snow.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Southwest winds increased overnight and will further ramp-up as the day progresses. Most of the past week saw winds eerily quiet, which allowed the recent bountiful snowfall to remain where it fell. Light to moderate winds Friday and Saturday drifted snow into thin slabs on leeward slopes at upper elevations. I found slabs up to eight inches thick and reactive to a skier's weight yesterday in Glacier Park. This morning, expect slabs to be wider and thicker than those found yesterday and will increase in size as the day progresses. We expect this problem to be mainly confined to upper-elevation terrain where there is still abundant dry snow to transport. However, with today's damaging wind speeds, expect a few locations at mid-elevations to develop slabs. These wind features will be found below ridgelines, downwind of saddles, and cross-loaded terrain features. Seek out sheltered terrain to find the best quality riding and a respite from the incessant howling.

    (3/27/2021) Increasing winds drifted snow into slabs that were reactive to the weight of a human.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Last night was the second consecutive night with a poor refreeze. Saturday, an observer noted wet loose slides beginning at 10:00 a.m. on steep mid-elevation southerly slopes. Another observer referred to the surface conditions as manky. With warm overnight temperatures at low and mid-elevations, expect more of the same today. The wet loose problem may creep up into the upper-elevations on sunny slopes sheltered from the wind. I noted tree bombs in this terrain, which resulted in large rollerballs from just a brief moment of sun in Glacier Park. If you or your machine is sinking below the surface more than a few inches, it is time to seek a different aspect or elevation. Slopes exposed to the wind have the best chance of maintaining drier snow. 

    (3/27/2021) Tree bomb triggering roller balls is a sign of an impending wet loose cycle. The best bet is to change aspects and get to colder snow.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    Weak layers buried in late-January can still ruin your day or life. Your weight can affect these layers where they are closest to the surface, such as slopes peppered with rocks or scoured by wind. Areas without a crust allow you or your snowmachine's weight to penetrate the snowpack easier than areas harboring a crust. In doubt, default to terrain around 35 degrees or less in steepness and free of rollovers or convexities.  

    (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

This season FAC adopted a new forecast platform that provides a 24 hour forecast period. Our previous product had an expiration of 11:00 p.m.and; generally, we are pleased with the new longer duration forecast, except for days like today. Sunday's weather forecast for the daylight hours and overnight couldn't be more different. Truly night and day. The warmest air temperatures of the week will lead to another day of wet snow instabilities. A cold front pushes into the area overnight with 0.5 - 0.75 inches of water and snow levels lowering to the valley floor. Wet snow hazards today will be a thing of the past by this time Monday morning, replaced by new snow hazards such as storm slabs. Therefore, today's avalanche product has returned to its old school roots with an expiration of 11:00 p.m. Sunday.

This past week's great dry snow riding is quickly diminishing. Saturday, I found dry snow on upper-elevation aspects that were either facing the wind or sheltered from the sun. The moist snow line crept up through the day and may have affected the dry snow I enjoyed by day's end. A party in the Middle Fork reported temperatures of 39F at 8:00 a.m. and wet loose slides on mid-elevation southerly aspects starting at 10:00 a.m. Another party turned around from their objective partly due to a loose wet slide and the manky snow conditions. With warmer overnight temperatures Saturday night, expect wet snow instabilities first thing this morning at low and mid-elevations. We have expanded the distribution of the wet loose problem to upper-elevation sunny southeast through west aspects to account for the warmer temperatures overnight and expected today. Slopes buffeted by today's stiff winds will remain much cooler than those sheltered from the winds.

There is a high wind warning for the Flathead Valley starting around 3:00 Sunday afternoon and lasting into Monday morning. Damaging winds are expected with tree fall and possible power outages. If you're going to brave the blustery conditions, expect to find some unusual conditions. First off, think about where your vehicle is parked at the trailhead. Is there a chance it could get hit by a falling tree or branches? If trees are swaying from the wind in the area you are recreating; you should probably move to a less exposed location.

Check out the latest installment of our weekly snowpack and weather summary in the media gallery below or here.

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