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Avalanche Forecast

Archived

Mar 24th, 2015–Mar 25th, 2015

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Snoqualmie Pass.

A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. This should cause a big increase in the avalanche danger over the west slopes on Wednesday.

Detailed Forecast

A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. Rain or snow should be heaviest in the Olympics and central to south Cascades Wednesday morning and shift to the north Cascades Wednesday afternoon and evening. Snow levels and avalanche danger levels will be a moving targets but the sure thing is they will be going up pretty rapidly on Wednesday.

The warming trend and initial snow will help build new upside down new storm slab where there is at least a few hours of snowfall of an inch or more an hour. This is very likely above treeline throughout the west slopes through the morning and then mainly in the north Cascades Wednesday afternoon and evening.

The warming trend and initial snow will also help build new wind slab on lee slopes. This is also very likely above treeline throughout the west slopes through the morning and then mainly in the north Cascades Wednesday afternoon and evening.

The change to rain should generally be seen in the south Cascades during the morning and in the north Cascades in the afternoon and evening. This is likely to begin to cause a cycle of loose wet avalanches on many slopes in most elevation bands.

Less recent snow and ample terrain anchors may limit the avalanche danger below treeline. Many areas at the lowest elevations do not have enough snow to cause an avalanche danger.

Snowpack Discussion

The storm last weekend caused 1-2 feet of snow above treeline in the Mt Baker area. At the NWAC station at the base of the Mt Baker Ski Area there was about 8 inches of snowfall and there was up to a few inches elsewhere along the west slopes.

Near the Mt Baker Ski Area on Sunday NWAC observer Jeff Hambelton reported small loose wet avalanches on the north slopes of Table Mountain. High on Heliotrope Ridge a skier triggered and was partly buried by a 1-1.5 foot storm or wind slab avalanche.

A fairly vigorous low pressure system moved east over the Mt Hood area last night to this morning and temporary winter-like conditions returned to the Cascades. New snow amounts this morning west of the crest generally ranged from 3-5 inches from Baker to Snoqualmie and from 8-12 inches from Crystal to Mt Hood. 

NWAC observer Dallas Glass has been camped above Paradise the past couple days and reports deep new storm snow of 1-2 feet and likely wind slab conditions this morning.

Forecaster Dennis D'Amico and NWAC observer Jeremy Allyn witnessed a couple of large skier triggered loose dry avalanches today in Silver Basin near Crystal Mountain.

Snowpack problems west of the crest for the time being should be in the upper or surface layers. The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

 

Problems

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.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.