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Avalanche Forecast

Archived

Mar 23rd, 2019–Mar 24th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal.

Human triggering of large persistent slab avalanches remain possible; especially in rocky, alpine terrain with a shallow or highly variable snowpack depth.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SATURDAY NIGHT: Partly cloudy / Light, southeasterly winds / Alpine low 1 C / Freezing level 1400 m.SUNDAY: Mix of sun and cloud / Light, easterly winds / Alpine high 2 C / Freezing level 1500 m.MONDAY: Mostly sunny / Light, northeasterly winds / Alpine high 2 C / Freezing level 1500 m.TUESDAY: Increasing cloudiness / Light, southwesterly winds / Alpine high 0 C / Freezing level 1200 m.

Avalanche Summary

Natural avalanche activity has tapered off with the cloudy skies and cooling temperatures. Concern remains for human triggering persistent slab avalanches on a layer of facets that are down 50-100 cm. Explosive control work on Thursday produced several large avalanches, up to size 3, on this layer and there continue to be reports of skiers experiencing whumphing (collapsing) of this weak layer in shallow or variable snowpack areas in the alpine.

Snowpack Summary

At upper elevations, 50-100 cm of well settled snow overlies weak facets (sugary snow) that were buried around March. 10th. which is currently the primary layer of concern for human triggering persistent slab avalanches.Not much further below the March 10th interface is a second weak layer of facets buried on February 19th. Recent loose wet and slab avalanches have been observed gouging into this faceted snow and entraining additional mass.The prolonged warm spell has transitioned sun exposed slopes in the alpine and all aspects at treeline and below towards becoming isothermal (0 C throughout the snowpack). In these areas that have entered spring conditions, the avalanche hazard will fluctuate greatly depending on the strength of the overnight freeze and how quickly the snowpack is warmed up each day. Check out this guide to managing avalanche hazard during spring conditions HERE.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.