Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
View on map

Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Yesterday, a rider intentionally triggered an avalanche large enough to bury a person on a buried weak layer.  These layers are found 1-4' below the surface, have been on pause this past week, and remain as dangerous as before the arctic intrusion. Snow and westerly winds return to our area and may form thin slabs especially downwind of ridgelines. Don't let cabin fever get the best of you today. Remain vigilant with terrain selection by choosing planar slopes less than 35 degrees in steepness.

Avalanche problems

  • Persistent Slabs

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

    Yesterday in the Swan, Cam intentionally kicked a refrigerator-sized cornice that initiated a dangerous avalanche on a buried layer of surface hoar on a northeast slope. Surface hoar or facets can be found 1-4' below the surface, resting on or just above the 1/13 crust on all aspects. Observations of avalanches, collapses, and propagation in snowpit tests have confirmed that this problem is more widespread and dangerous on shaded slopes.  Our Persistent Slab problem is difficult to manage, and we recommend selecting terrain free of rollovers with slope angles less than 35 degrees. 

    (2/14/2021) Intentionally triggered persistent slab avalanche. Crown averaged 2 feet thick and propagated 100 feet wide. Triggered by cornice fall.

  • Wind Slabs

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

    After a week of easterly winds forming slabs in atypical locations, today marks the return of westerly flow and possible thin wind slab development on the easterly side of the compass. Older slabs formed earlier in the week are becoming more stubborn to trigger but are large enough to prove dangerous. There is plenty of low-density snow available for today's light winds to transport onto leeward slopes.  If winds reach a threshold level, thin slabs may form. Expect them to increase in thickness as you gain elevation, feel denser, and possibly have a rounded or teardrop appearance. If you encounter these features, change course and aim for higher quality and safer conditions in areas sheltered from the wind. 

    (2/14/2021) null

Avalanche Discussion

The frigid, arctic air mass is finally loosening its vise-like grip over our area. This unique pattern of well below average temperatures and easterly winds entered the area Sunday, February 7, and lasted for eight days. The cold spot with these events is generally the John F. Stevens Canyon - Marias Pass corridor, and this one was no exception. The BNSF Marias Pass weather station dropped below zero degrees Fahrenheit on Sunday the seventh and did not climb above zero until Sunday the fourteenth. An astounding 142 consecutive hours of sub-zero recordings. To add insult to injury, there was an eight-hour window where the temperature stayed at or below -41 F.

Temperatures like these have put the buried surface hoar layer above the 1/13 crust on pause. Weak layers generally heal over time, but the temperatures we experienced this week did not allow for any strengthening. Essentially, this layer is as weak as it was eight days ago. Other slopes have facets sandwiching the crust, and these lost strength throughout the week due to a very large temperature gradient in the snowpack. In locations such as Marias Pass, the large temperature gradient could be considered astounding. I don’t mean to sound like a Negative Mark, but let’s not forget about the surface snow. It fell as low-density powder a week or more ago and has been subjected to the cold even more so than the buried layers. In areas sheltered from the wind, the snow may appear even lower density than when it fell due to faceting. Riders may trigger Loose Dry sluffs today, but, more importantly, the surface snow will be tomorrow's next weak layer.

Today’s temperatures should reach mid to upper 20’s at low and mid-elevations and should feel relatively balmy. After being cooped up in the house for the past week, we could all use a dose of powder to help us navigate these uncertain times. Step out gingerly and thoughtfully. We recorded nine consecutive days of triggered avalanches a week ago, which resulted in several close calls; two riders carried in separate accidents, and one fatality. Ease into the backcountry by enjoying low-angle powder until our Persistent Slab problem improves. Besides, the riding is way better on lower angle terrain where you are not scraping down onto the crust. 

Regions covered