Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

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

More snow and wind, plus fluctuating freezing levels should be enough to drive dangerous avalanche conditions at Snoqualmie Pass on Friday. Take the time to look for heavy over weak snow as you travel. If you find it or red flag signs of instability such as cracking or recent avalanches, avoid slopes over 35 degrees for the duration of the storm. 

Problemi valanghivi

  • Storm Slabs

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

    Take the time to check the new snow to see how it has bonded to the prior surface or if there are interstorm layers of concern. You could find that fluctuating freezing levels create some heavy snow falling on weaker snow (upside-down snowpack) which is a good recipe for Storm Slabs. Using hand pits can help highlight any potential weak layers and small test slopes can show you how those layers may be reacting to your weight. You should check all of the snow above the easily identifiable Christmas Crust, which is more deeply buried as you ascend in elevation. In previously wind-loaded areas, slabs could be even thicker and react differently. If you see signs of cracking, blocks of snow failing easily, or recent avalanches, then you should avoid slopes over 35 degrees til this storm plays out.

    (12/25/2022)

    Several small slab avalanches failed in the sleet earlier this week. While we don't expect sleet on 12/30, you could see similar-sized slides.

    Photo: WS DOT, SCR Avalanche Crew

Avalanche Discussion

Friday should be a final round of precipitation before a relative break hits Snoqualmie Pass over the weekend. It’s been a wet and stormy week, with several rounds of rain, freezing rain, sleet, snow, and wind. This dynamic weather has sculpted and changed our snowpack in a number of ways. Most recently, strong winds have begun to form Wind Slabd and build new and somewhat sensitive cornices. These are more prevalent near ridgelines or rocky features and were observed by NWAC forecasters on Thursday while effects of the wind were reported via multiple public observations.

Prior to the winds, an easily identifiable crust was formed by the rain and freezing rain over the Christmas weekend. This crust was later buried by about a foot of snow at mid to upper elevations. At lower elevations or in wind-scoured areas, the Christmas Crust is much closer to the surface. Its thickness and depth vary by elevation but it should be the baseline of any snowpack tests you perform for the foreseeable future.

Along with the crust being formed, the rain also resulted in a myriad of wet avalanche problems around the Pass. We have been forecasting Glide avalanches recently, but have decided to pull the official problem for Friday. The last confirmed Glide avalanche was on 12/27 and although the lower snowpack still contains plenty of water, we believe the likelihood of one of these failing has decreased.

Unfortunately, with tomorrow’s new round of precipitation, a bump in freezing levels may allow for some rain to return to the lower elevations. In many areas, there’s not much snow over the Christmas Crust to become a problem below the forecasted rain line. That said, if you find that rain is falling on dry snow, be aware that wet avalanches could occur, likely in the form of Wet Loose. Furthermore, any rain may help to further swell creeks and rivers. At least one river was found to have blown out this past week and there may be more holes or other natural hazards than the last time you visited the mountains.

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