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Avalanche Forecast

Archived

Feb 13th, 2019–Feb 14th, 2019

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

Regions

Snoqualmie Pass.

If you venture in the backcountry be certain of your ability to avoid avalanche terrain. Wind and more snow will stress the snow and make it easy to trigger very large and life-threatening avalanches. Continue to avoid steep slopes and put plenty of space between where you travel and large avalanche paths.

Discussion

Snow and Avalanche Discussion

Observers have reported a widespread and prolonged cycle of avalanches involving a variety of aspects and elevations. Common characteristics of these avalanches are very widely propagating crowns about 3 feet deep. Local ski patrols, highway workers, and backcountry travelers all reported extensive avalanching on the night of the 11th, into the 12th, with triggered slides and a few naturals continuing into the 13th. While some avalanches ran in storm layers in the upper snowpack, many appear to be running an old weak faceted layer over 3 feet below the surface. Dangerous conditions and road closures have limited our ability to gather more detailed information from the Snoqualmie Pass area. 

Snoqualmie Pass has received over 80 inches of snow since February 8th. More cohesive snow on the 11th and a couple wind events are building slabs along the I-90, Snoqualmie Pass corridor. In addition to avalanches, all the deep snow is building concern for Snow Immersion Suffocation, or tree well hazards. Travel in the mountains with partners and keep them in sight.

A natural avalanche in Icicle canyon. Grindstone Mtn, SE, 6,600ft. Photo: Matt Primomo

Snowpack Discussion

Regional Synopsis coming soon.

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.

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.