Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Saturday, a  rider triggered a large avalanche that failed deep in the snowpack. This confirms a person's weight can still affect weak layers buried three to six feet below the snow surface. While instabilities in the new snow are found at all elevations, the most dangerous are where winds continue thickening and stiffening soft surface slabs. If the sun makes an appearance, expect sluffs to run surprisingly long distances. Continue to choose slopes less than 30 degrees in steepness free of rollovers and overhead hazards. 

Avalanche problems

  • Storm Slabs

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

    Many locations received 6-8 inches of new snow from the Thursday storm.  In some areas, this was deposited onto a thin crust formed earlier in the week. Cam found evidence that riders triggered numerous thin slabs in the southern Whitefish Range Friday. In the northern Whitefish Range, Blase noted a slab triggered by a snowmobile on a steep low-elevation slope Saturday. He also noted easy failures in hand pits in this layer that had settled into a slab due to warming temperatures. Slabs will be thickest in areas where winds typically drift snow - lee sides of ridgelines or gullies or behind terrain features on cross-loaded slopes. Utilize hand pits or small test slopes to determine the bonding to the underlying layer. If you find instabilities, manage the problem by choosing low-angle terrain.

    (2/27/2021) Small slabs involving recent snow triggered by riders on a short, steep slope.

  • Persistent Slabs

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

    A skier triggered a Persistent Slab avalanche Saturday in the Stryker Peak area of the Whitefish Range.  The fracture line ranged from 3-5 feet deep, but from second-hand reports, the riders were apparently able to ski away unharmed. In a Level Two avalanche class in the southern Whitefish Range, snowpit tests confirm weak layers buried 3-6 feet deep can still propagate a fracture.  This low probability, high consequence problem is best managed with terrain selection. Slopes less than 30 degrees that are the same shape from top to bottom are the best bet. Choose areas with clean runouts free of surface obstacles that can magnify the consequences of getting caught and carried.

    (2/27/2021) Diagram outlining a large, unintentionally-triggered slide in the northern Whitefish Range Feb. 27.

Avalanche Discussion

We have dropped the avalanche danger at upper-elevations to MODERATE, or level two of five. Actually, it is more like level two.five (2.5). Something we affectionately refer to as scary MODERATE. This is the first day since Saturday the 20th that we have been at this level. Despite receiving a report of a near-miss involving a skier-triggered Persistent Slab avalanche in the Whitefish Range Saturday, we feel that the danger level is not CONSIDERABLE. We try to call it like it is and not cry wolf.

You may have noticed that our outlook forecast for Monday looks a bit odd. We are expecting the danger to rise to CONSIDERABLE at mid and low-elevations. A warming trend with increasing sunshine and temperatures should initiate an impressive wet snow avalanche cycle on sunny aspects. For those fortunate enough to recreate in the backcountry this week you have found bountiful dry snow with very little wind effect. Tomorrow’s warming should weaken bonds in the dry snow resulting in sluffing which may run surprisingly long distances. There is substantial snow in avalanche paths to entrain and we expect some of these slides to be impressive in size. This will be particularly true in areas with larger terrain such as the Flathead Range and Glacier Park. Unfortunately, there may be a lot of good riding terrain ruined during this cycle.

This past week storm Snow Water Equivalent ranged from 3.8” at Flattop, 2.4” in Noisy Basin with 1.8” at Stahl Peak. This boosted our end of the month SWE to 103% of the average for the Flathead River Basin. Flattop leads the charge with 116%, Noisy has 106%, with Stahl at 90%.

For a review of the past week's snowpack, weather, and avalanche summary check out this video.

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