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Avalanche Forecast

Archived

Apr 3rd, 2016–Apr 4th, 2016

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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

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Winter will make a brief comeback on Monday! The avalanche hazard should increase in the afternoon as shallow storm slabs become more sensitive and with elevation as fresh wind slabs build on lee aspects. The avalanche danger will quickly decrease further east from the Cascade crest due to minimal new snow accumulation. 

Detailed Forecast

Winter-like conditions will make a brief comeback on Monday as a front passes through early Monday morning and cool post-frontal showers follow in westerly flow. The avalanche danger will quickly decrease further east from the Cascade crest due to minimal new snow accumulation. 

A cooling trend during the day Monday should generally help new snow bond to older moist snow and surface crusts. Even with the cooling trend, subtle daytime warming will make shallow storm slabs possible by the afternoon. Also, heavier showers depositing graupel layers may locally make storm slabs more sensitive to human triggering.  

Persistent westerly winds will transport new snow onto lee slopes near and above treeline Monday and Monday night. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers. The wind slab problem will be elevated above treeline where more snow and stronger winds will build fresh wind slabs on lee aspects. 

Loose wet avalanches will not be listed as a primary avalanche problem Monday. However, small loose wet avalanches involving new storm snow will be possible on any steeper solar slope during prolonged sunbreaks Monday. 

The likelihood of cornice failure will lower Monday due to cooler weather. However, cornice releases can be unpredictable during the spring so continue to be aware of the overhead hazard and that cornices can break much further back than expected along ridges.

Although not listed as an avalanche problem, large, powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces.

Snowpack Discussion

Weather and Snowpack

A large upper ridge has been over the Northwest for several days resulting in warm and dry weather. A spring avalanche cycle occurred in most areas over this stretch, likely peaking Thursday or Friday during the warmest temperatures and lightest winds. After a stormy March, the snowpack has undergone significant settlement over the last week. 

Frequent March storms have built unusually large cornices along many ridges.

No persistent weak layers formed earlier this winter are layers of concern as we transition to a spring snowpack along the east slopes. 

Recent Observations

NWAC professional observer Tom Curtis was out on Wenatchee Ridge near Lake Wenatchee Wednesday, 3/30 in the 2-4000 foot range and found many slopes melted out. On slopes still holding snow he found natural and easily triggered loose wet avalanches on all solar slopes in the top 15-20 cm of snow.

Tom was out yet again on Mt Lichtenberg near Stevens Pass on Thursday and found widespread large natural loose wet avalanches on nearly all solar aspects with easy to trigger loose wet avalanches on non-solar slopes.

A report on Turns All Year for the Chiwaukums described big rollerballs and big resulting debris piles on Thursday.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.