Avalanche Forecast

Archived

Feb 5th, 2015–Feb 6th, 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 avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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On Friday, avalanche conditions should become increasingly dangerous with elevation and closer to the Cascade crest. Backcountry travel above treeline is not recommended.

Detailed Forecast

Moist and mild southwesterly flow will carry wet fronts across the area Thursday night and Friday. Snow levels will remain high, around 6500-7000 feet, before beginning to cool later Friday afternoon. The avalanche danger will be much higher near the Cascade crest where more precipitation will have been received.

Loose wet and wet slab avalanches are possible below and near treeline due to rain on snow, with the potential to entrain snowfall received earlier this week above the most recent crust.

Higher density snowfall will overlie lower density snow above treeline, making for unstable storm slabs especially on lee aspects in the alpine.

Friday will be a poor day for backcountry travel no matter how you cut it.

Remember, due to the unseasonably low snowpack especially at lower elevations, numerous terrain hazards such as open creeks, partially covered rocks and vegetation are widespread.

Snowpack Discussion

Mild weather with sunny days or minor rain or snow was seen in the Cascades from about January 26th to about January 31st. East of the crest this should have caused some consolidation and stabilizing. A surface crust will have formed on solar slopes but less so on shaded slopes or at higher elevations. Surface hoar formed on shaded and north slopes in some areas in fair weather during this time.

Periods of light snowfall was seen this week east of the crest with more at higher elevations in the northeast and central east zones. Steady but generally light precipitation was seen during the day Thursday with a gradual warming trend; NWAC Washington site and the Hart's Pass Snotel had risen to 32 deg F as of 5 pm with several inches of denser snow accumulated through the day.

NWAC pro-obs and North Cascade Guides reports last week in the northeast and central east zones have the January 15th facet/crust layers at 40 cm-1 m below the surface with the facets starting to turn to rounded grains and not reactive or not releasing in pit tests. So the January 15th facet/crust layers appear to be strengthening and stabilizing by late January. This problem will be removed from the central east zone but retained in the northeast zone until more information becomes available there.

Other private groups in the Washington Pass area on February 2 and 3 report some upside down densities in the recent snow from earlier in the week and natural and ski cut loose dry avalanches.

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.

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.