Bollettino valanghe

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Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Dangerous conditions will extend into Thursday as you could trigger large and destructive avalanches at upper elevations. Difficult travel and poor visibility have limited information after a large storm and widespread avalanche cycle earlier this week. Be prepared to make your own assessment of the recent snow and more deeply buried weak layers.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Use extra caution around slopes 35 degrees and steeper at upper elevations, especially on leeward sides of ridges. Steer around convex roll-overs and unsupported slopes.  A huge load of recent snow and storm interfaces still need time to bond. 

    Widespread, very large avalanches occurred on Monday in the storm snow. While natural activity has tapered off, you could still trigger these avalanches. A weak layer of facets and surface hoar was buried on the 26th and could still be triggered by backcountry travelers. Manage the risk by minimizing your exposure to avalanche terrain. 

    (3/1/2022) A deep crown of a slab avalanche at the base of cliffs. SE, 6500ft near Azurite Pass. Photo: Steph Williams

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2.5–3.5

    Information on the status of this dangerous avalanche problem is still limited. Until we know more, put a wide buffer between where you travel and large start zones and avalanche paths.  If you managed to trigger persistent weak layers, a resulting avalanche could be destructive and unsurvivable. 

    While the late January facets have recently been dormant, they've remained weak on shaded aspects at middle and upper elevations. A huge load of recent snow may have made it easier to trigger the layer. Near the Cascade crest, you can find this layer at least 5ft deep and sandwiched between two crumbly crusts. Further east this layer is closer to the surface and not far below the most recent storm interface from Feb 26th. Very wide avalanches were last observed on the weak layer on February 12th. See more images and details below

    (2/12/2022)

    A natural D1.5 avalanche, occurred Feb 10 or 11th, likely on the late January pwl. Porcupine Pk, E, 7,400ft.

    Photo: Tino Villanueva

Avalanche Discussion

Heavy snow, rain, and difficult travel limited access and information since Monday. A major question that remains unanswered is whether avalanches from this recent cycle ran on the late January facets. Near Harts Pass, observers measured 55" of storm snow which settled to about half that height by March 1st. The weather station at Washington Pass recorded an overall gain in height of snow  38" between the 26th and the afternoon of the 28th. Since then, most precipitation has fallen as rain up to 6,500-7,000ft. Most elevations saw enough rain to create moist to wet snow surfaces and difficult travel. Cooling temperatures should minimize the threat of wet avalanches on Thursday. If you find wet, unsupportive snow, consider the potential for triggering wet slides.

The storm brought a widespread cycle of large to very large avalanches across the zone. On Tuesday, observers reported triggering a small avalanche, about 1 foot deep on an E-SE aspect at 7,000ft near Harts Pass. The slide started as wet loose that then broke into a slab 10-15 feet wide. Near the Silverstar trailhead, I found the February 26th facets preserved under almost 2 feet of recent storm snow and resting on a crust. Snowpack tests produced sudden results (CTM (SP)) on the layer. Numerous avalanches to size D2.5 occurred on S-SE aspects of Delancey ridge. It appeared that some ran in dry snow on Monday with wet avalanches running later in some of the same paths. On Monday, observers near Harts Pass reported widespread natural avalanches in the new snow, even on small, low-angle features and paths that don't frequently avalanche. By the evening of the 28th, they reported 3 feet of accumulated storm snow. 

On Sunday, observers in the Cutthroat creek area found touchy avalanche conditions with about a foot of new snow fracturing easily on steep slopes. One large soft slab up to 1.5ft deep was noted from a SE aspect at 6,700ft. On a similar slope, observers reported remotely triggering a slab avalanche, likely on the 2/26 interface. Numerous small (D1-1.5) loose avalanches were also observed from upper elevations. NWAC Forecaster Josh Hirshberg found the late January facets about 2.5ft down on a north aspect in Cutthroat creek, with propagating test results (ECTP23, PST 30/100 End). On Friday observers found surface conditions to consist of a mix of weaker snow grains; patchy surface hoar and near surface facets on northerly aspects while widespread surface hoar had grown on southerly aspects. These layers could become the next, widespread problem as the storm tapers off. 

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