Bollettino valanghe

West Slopes North

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Stormy conditions will develop by Sunday morning. Up to a foot of new snow and strong winds will increase avalanche danger through the day. Avoid steep, open slopes where you observe wind drifted snow and stick to wind protected terrain. Expect rain at low elevations.

Problemi valanghivi

  • Wind Slabs

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

    Very strong winds could create an unusual wind loading pattern. Don’t be surprised to see slabs scattered about mid-slope and at valley bottom in addition to just below ridgeline. Wind slabs could be more reactive, propagate wider and run farther where they form over crusts or weak snow. Danger will be the greatest at the very end of the day when the storm is at its peak. 

    Given challenging weather conditions, the best policy will be to start and finish your day in simple and sheltered areas instead of trying to assess bigger terrain on a slope-by-slope basis. Natural avalanches could occur during periods of heavy snowfall and higher wind speeds. If you experience heavy snowfall look for unstable slabs on all steep terrain, not just in wind loaded areas.

    Use small, wind loaded feaures to look for and test wind slabs.

    Photo: Jason Speer - Baker Mountain Guides

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Expect a half to a full inch of rain at elevations up to 4000’. There isn’t a ton of dry, unconsolidated snow at lower elevations to react to rainfall but there's enough that wet loose avalanches are still possible. Rain could also cause cliffs and other steep features holding snow to shed onto your head.  Look for snow falling from rocks and trees and keep an eye out for rollerballs and other signs of wet avalanche instability. Small wet avalanches could still do some damage if there are terrain traps in the runout below.

     Rollerballs and gooey snow are signs that wet loose avalanches could occur in steep terrain.

    Photo: NWAC Public Obs

Avalanche Discussion

The wind forecast met expectations Saturday with steady moderate winds gusting to the mid-30s all day long. Snowfall didn’t pick up until the afternoon and what did come down wasn’t observed as enough to provide the raw material for fresh wind slabs. Crusts were found to hold the loose snow below in place. No new avalanche activity was reported and in general, it was a quiet day. Fresh snow is again on the horizon.

New snow and wind slab layers will form on a variety of snow surfaces including crusts, previously wind affected snow, and possibly even some surface hoar in the most protected terrain. On Friday surface hoar and an inch of weak new snow were found at the surface, but it’s questionable how much of it survived between the sun Friday and then the wind on Saturday.

Another question mark in the snowpack is a layer of slightly weaker snow just above the stout rain crust that formed last weekend. This layer was likely the culprit in numerous natural and human slab avalanches reported this week. Though most were shallow, some showed wide propagation. Most interesting is the fact that backcountry travelers continued to trigger them up to three days after they formed.

Below the rain crust, the snowpack consists of alternating layers of crust and dense, rounded grains. There are no layers of concern but the snowpack has not undergone a true transition to spring. This could make for some rather large avalanches whenever more normal spring temperatures and sunshine decide to show up.

This is the last avalanche forecast for the 22/23 season. NWAC will continue issuing mountain weather forecasts each afternoon at 2:30 pm through April. It's been a great winter - still is winter it turns out despite what the calendar says.  Even better has been the opportunity for us to connect and get out into the mountains with people from all the different backcountry communities out there. Please continue to help support your backcountry friends by letting others know what you find in the mountains by submitting an observation. Have an awesome spring and summer and see you next winter! Irene and Lee

Regioni coperte