Bulletin d’avalanche

Presidential Range

Mount Washington Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Slabs of wind blown snow will build on eastern aspects in the middle and upper elevations throughout the day. Yesterday’s evidence of large natural avalanches suggests that slopes may be unstable with an elevated sensitivity to human triggering. Avoiding slopes loaded with new snow or areas that have not previously avalanched will increase your safety margins.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Today's snow and wind will build new slabs upon the older ones that are still trying to stabilize. The timing of Considerable avalanche danger may be delayed until accumulations and wind loading peak sometime this afternoon. The important factor to recognize is that areas where avalanches did not occur have now become the lingering “hangfire” that should be avoided. Keep in mind an avalanche from newly formed slabs may have the ability to step-down into larger existing slabs formed over the weekend, contributing to a much larger avalanche. 

    The sensitivity of recent slabs is still highly variable and the distribution is somewhere between specific and isolated. Firm snow, that is of 1 finger hardness, lies over soft snow which is around fist hard in many locations. This is the setup that can create large human triggered avalanches in steep terrain.

Avalanche Discussion

Several variables are driving the Considerable danger rating today. Yesterday's alarming evidence of large natural avalanches in many specific locations is paramount. Tuesday night into Wednesday morning there was a serious risk of natural avalanches from wind blown snow due to the touchy sensitivity of recent slabs. Old slick bed surfaces, upside down snowpack structure, and continuously loaded slopes culminated in this short duration event. 

Crown lines ranged from 1 inch thin, superficial wind skin, to around 4 feet deep large D2.5 size avalanches. Runout zones were filled with avalanche debris which covered previously exposed rocks and vegetation. Many of the crown lines and some debris were refilled by wind-transported snow or sculpted by strong winds. 

Today it could be difficult to see the evidence of yesterday’s avalanches unless you look at photos of days prior. Understand that not all avalanche paths slid, and that there are still pockets of potentially unstable snow lingering above you as you climb in exposed places. North aspects higher in the terrain that did not gain prolonged sun exposure are concerning. Shade can inhibit the stabilization of snow and allow an avalanche to step down into older slabs that are still undergoing sintering. A step down avalanche is harder to predict and can entrain way more snow than the current avalanche risk would have you believe. Early identification of the lingering slabs is crucial to route selection. 

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