Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
View on map

Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche danger will remain LOW through the daylight hours but will rise overnight as snow returns to the Flathead. Expect dangerous avalanche conditions to develop Monday. Today, keep an eye out for thin isolated wind slabs while steering around convex slopes and areas harboring a shallow snowpack where you could trigger a large avalanche.  

Avalanche problems

  • Storm Slabs

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

    If the weather forecast holds, we expect a storm slab problem to develop during the early morning hours Monday. This problem should not be a concern during the daylight hours today. New snow will fall on widespread weak surfaces such as surface hoar and faceted snow, allowing slides to propagate wider than expected. In areas exposed to the wind or sun, snow will cap crusty surfaces and enable slides to travel long distances. If you are out in the early morning hours Monday, utilize hand pits and small test slopes to see how well the new snow is bonding to the layer below. Expect this hazard to increase through the day Monday.

    (1/17/2022)

    Multiple crowns observed failing 1 to 2 feet deep. These likely failed sometime around Wednesday 1/12 during a warm, wet, and windy storm. 

    Photo: Mark Dundas

  • Deep Persistent Slabs

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

    Triggering a slide on a deeply buried weak layer remains a low probability - high consequence problem. Areas most susceptible to triggering are where the snowpack is either shallow, such as wind-scoured slopes and terrain peppered with rocks or has a convex slope shape. The only way to know if the slope you are on harbors these layers is to dig to the ground. Even then, snowpack tests don't always give clear signals. We recommend using terrain to navigate this problem: Choose planar slopes free of convexities, avoid rocky areas where weak snow develops, and steer around thin wind-scoured areas in favor of slopes holding a deeper snowpack.

    (1/17/2022)

    Crown line of a deep persistent slab avalanche. Crowns estimated at 6 to 8 feet thick. 

    Photo: Mark Dundas

Avalanche Discussion

This week's benign weather resulted in observations from all forecast zones that followed the same theme of a weakening snow surface in sheltered locations and wind-affected snow in areas open to the wind. Saturday's observations were no different. Clancy and Rick, the January FAC intern, found widespread surface hoar up to 7200 feet in the Middle Fork. This week's cool, clear weather allowed this weak layer to grow up to 1 cm in size. Above 7200 feet, winds had knocked over the surface hoar or turned the snow surface to wind crust or thin wind slabs. Below 5000 feet, they found the 1/20 rain crust buried under 3 inches of near-surface facets. Above 5000 feet, the crust is decomposing on sheltered northerly slopes and covered by 7 inches of near-surface facets (1-2mm). Observations from the WMR side-country reported large-grained surface hoar on all aspects from 5700-6700'. An observer in the Middle Fork reported widespread surface hoar on all aspects sheltered from the wind. Above 7500 feet, they found wind scoured surfaces and isolated wind slabs.

A storm with Pacific moisture will enter the area this afternoon and increase intensity throughout Monday. If snow totals reach forecasted amounts, we expect to see a natural avalanche cycle on multiple aspects and elevation bands. We currently have two of the three ingredients needed for a slab avalanche. They are widespread well-developed weak layers and a sliding surface consisting of a sun, rain,  or wind crust. We will have the third and final ingredient if the new snow forms a slab. Avalanches may propagate long distances due to the abundance of weak layers at the surface, with slides having the potential to travel long distances on the underlying crust. After nearly a week of LOW avalanche danger and green light conditions, we will need to dial back terrain choices Monday and into the workweek. 

 

 

Regions covered