Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Very dangerous avalanche conditions are expected to develop at upper elevations with heavy snowfall and strong winds. Large natural avalanches could run overnight into Tuesday morning, and instabilities may linger through the day. Stay off of and well out from underneath steep slopes at upper elevations, and stick to low angled slopes near and below treeline while the snowpack adjusts to the load. 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2

    Snowfall should stack up quickly overnight into Tuesday morning, despite the storm having underproduced on Monday. Strong winds should rip through the pass and buffet exposed locations, which could create thicker and more cohesive slabs. Cracking within the new snow and fresh crowns on steep convex slopes are all indicators that storm slabs could be easily triggered or run naturally. 

    Stay off of and well away from steep slopes at upper elevations because we're likely to be coming out of a natural avalanche cycle by Tuesday morning. Many of these could be large and run long distances. The new snow is likely to remain touchy to human triggering during the day. You might be able to trigger slides from a distance and from below, so give the snowpack some time to adjust before venturing onto steep slopes.

    Example storm slab avalanche from earlier this season.

    Photo: Alexa Cathcart

  • Deep Persistent Slabs

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

    A thin weak layer resting on a slick crust from mid-January is anywhere from 3-5ft down in the snowpack. We've been continuing to find test results that indicate propagation potential on this layer, and it keeps getting deeper. The last activity we know of on it was from February 8-13th. Some of these were quite large and surprisingly wide. With the added snow and wind load, we may see more activity begin to occur on this deeper weak layer. The resulting avalanches could be very large and destructive. 

    To be on the safe side, steer clear of runout zones with large, overhead avalanche paths as the snowpack adjusts to the added stress.

    (2/12/2023)

    Very wide crown spanning most of the south face of Jove Peak. This slide very likely occurred during the middle of the day on Sunday.

    Photo: Public Obs

Avalanche Discussion

Avalanche Accident Colchuck Pk, East Central Zone

We’ve received preliminary information of an avalanche incident on Colchuck Peak, SW of Leavenworth, WA. (East Central Zone) The accident occurred on Sunday, February 19 and involved a group of 6 backcountry travelers. Three members of the group are suspected to have been buried and perished in the event. Another sustained injuries and was evacuated by SAR.  Rescue efforts are ongoing. NWAC is working with Chelan County Sheriff’s office and will make updates as more information becomes available.

 Forecast Discussion:

Monday's weather forecast underproduced, but Monday night into Tuesday should bring the snowfall and wind we've been talking about. A natural avalanche cycle could occur overnight and could persist into the day on Tuesday. We could see a rogue very large avalanche, but theres uncertainty on how reactive deep persistent slabs may become.

As of this writing, the pass has picked up 9-16" of new snow since Friday. These amounts are expected to increase rapidly overnight. SPMR reported triggering a number of 12" deep slabs with morning control work on Monday. Others reported that the new snow bonded well, especially at lower elevations. On Sunday small wind slabs were easily triggered above 5,000ft on Sunday, as rapid wind loading and steady snowfall occurred. Dry loose avalanches were also easy to trigger on steeper slopes. Large column tests have continued to indicate the potential for avalanches to propagate on the MLK crust, although the layer is gaining strength. This layer is now 3 to 5ft below the surface. 

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