Bollettino valanghe

Purcell Mountains

Idaho Panhandle Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 5 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Multiple crusts intermixed with cohesive snow layers creates slippery sliding surfaces for fresh slabs 1 to 2 feet thick to fail on. These slabs will be deeper and potentially more reactive on northerly and easterly-facing slopes where winds stacked harder layers over softer ones. Go around places that look smooth and rounded, and build an extra buffer traveling near or below slopes around 35 degrees where you see cracking in the snow or evidence of active wind transport along ridges. 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Since March 11, the Selkirk and Purcell Mountains received 1 to 2 feet of new snow. Increasing temperatures and fluctuating rain-snow elevations mid-cycle deposited a firm rain crust across the mountains up to 6,600 feet in the Southern Selkirks. Then, cooler temperatures returned and heavy snowfall quickly built another layer of cohesive slab above this harder interface. The recipe to trigger a dangerous avalanche quickly came together in addition to inverted slab layering below the mid-storm crust where softer layers are underneath harder ones.  

    With more time, these concerning storm interfaces will start to bond, but it could take longer than expected to heal. Areas below ridgelines, adjacent to rocky outcrops, and around convex terrain features are where winds likely enhanced slab stiffening and where these slabs may be more reactive. If the weather Sunday is sunnier or warmer than forecast, the new snow could quickly lose cohesion and start to sluff from steeper terrain on slopes that see direct sunshine.

    An annotated photo of slab hardness and test results in a wind-drifted area on a north-facing slope around 5,700 feet. Slab depths have increased since this photo was taken. West Cabinet Mountains. 

    March 11, 2026.

    Photo: Chris Bilbrey

  • Persistent Slabs

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

    A cohesive slab 3 to 5 feet thick overlies two buried surface hoar layers, with slab depths continuing to increase during the current storm. One surface hoar layer was buried at the end of January (1/28), and the other in mid-February around Valentine’s Day (2/14). The overlying slab has stiffened and settled due to wind, warmer temperatures, and natural settlement within the snowpack.

    As the slab has strengthened, the likelihood of human-triggered or natural avalanches has decreased. However, persistent weak layers always carry uncertainty, and these layers are currently being tested by rapid loading from the ongoing storm. If one of these layers were to become reactive, the potential remains for large to very large, destructive avalanches with serious consequences.

    Large surface hoar up to 8mm in size is visible to the naked eye at the January 28th interface. This layer is now found 3 to 5 feet below the surface and was exposed here after the overlying slab failed and slid downslope during a propagation saw test.

    March 9, 2026.

    Photo: Jackson George

Avalanche Discussion

The last stormy period added a nice boost to the mountain snowpack and for the Silver Valley, it was the biggest storm of the season - and maybe the past few seasons too. Storm totals range 6 to 20 inches in the Purcells, 12 to 22 inches in the Selkirks, 24 to 37 inches in the West Cabinets, 38 to 40 inches in the East Cabinets, and 35 to 58 inches in the Bitterroots-Silver Valley. This amounts to 1.5 to 3 inches of Snow Water Equivalent (SWE) in the Selkirk and Purcell Mountains and 2.7 to 5 inches of SWE in the Cabinet and Bitterroot Mountains. The Lost Lake SNOTEL, just south of our southern forecast zone, in the St. Joe Mountains received a staggering 7.1 inches of SWE in four days.

At the onset of snowfall on March 11, the existing snow surface was very firm - slide for life firm. This was the product of multiple days of above freezing temperatures and light rain from March 7 to 9, then a strong cold front locked up the surface. We don’t know how high in elevation this hard interface existed before the last round of snow, but remote weather stations suggest the warming regime climbed well into our upper forecast elevation band to near 7,000 feet - maybe the highest peaks in the East Cabinet Mountains excluded.

Shortly after the storm delivered around a foot of snow, a warm tongue of air progressively drove the rain-snow line higher in elevation. This laid down an inverted slab over the old melt-freeze crust. Despite not being a prolonged event, the rain line early on March 12 climbed higher than expected and enough liquid fell to saturate the surface. Then a strong cold front along with violent winds helped plummet temperatures and the snow surface flash froze. This created yet another rain crust. Above the rain line, strong to extreme winds built a hard wind-packed interface. 

Fortunately, cooler temperatures graced the rest of the stormy period and several days of heavy snowfall added to overall slab depths increasing potential avalanche size. All said and done, we now have an upper snowpack with complex layering that could vary quite a bit across the same zones or neighboring areas. An avalanche that fails in the near-surface layer cake has increased chances to either take you for a long ride or carry higher consequences like a full burial. Slides that encompass entire start zones or adjacent terrain features still carry the threat to step down into one of two surface hoar layers that have trended more stubborn in recent weeks. These layers still sit patiently waiting for a larger trigger like a large Storm Slab avalanche, cornice failure, or rapid input from liquid water to fail.

Storm snow hazards are often elevated during and immediately after a storm. How long they linger usually depends on what the weather does. Does it stay cool or warm quickly? Does the wind continue to transport the snow onto leeward slopes helping thicken fresh slabs? Or does an anomalous amount of warm air and rain move in and saturate the recent snowfall? Well…some, part, or all of the above looks to happen over the next week.

---

IPAC is now on the Avy app! View, submit, and share observations on the go using the AvyApp. Your backcountry observations are critical for building our avalanche forecasts. Avy provides a centralized location for core trip planning, and you can view streamlined, up-to-date avalanche and weather forecasts for your selected zone, using offline caching. Download Avy today - App Store and Google Play.

Regioni coperte