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Avalanche Forecast

Archived

Mar 29th, 2018–Mar 30th, 2018

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

Olympics.

You will be able to trigger a slab avalanche Friday on specific terrain features. You can avoid triggering these avalanches by avoiding steep roll-overs (convexities), unsupported features, and larger terrain of consequence on these loaded slopes, form north to east facing. A strong March sun affects the snow rapidly and can quickly create a Loose Wet avalanche danger if the sun comes out for an extended period of time.

Detailed Forecast

Evidence of recent Slab Avalanches as well as a variety of snowpack tests Thursday, indicate it will still be possible to trigger a slab avalanche on steep terrain features, such as roll-overs or unsupported slopes that have been loaded with wind transported snow. These lee slopes will vary from north to east facing, mainly near and above treeline. The layer of concern is the interface of a firm crust layer, buried about 1.5 ft below the surface. Weak snow above this crust is making avalanches possible on this layer. It will be important to avoid steep, large terrain or convexities in smaller terrain on these north through east facing slopes at mid and upper elevations.

Daytime warming and sun breaks Friday will make shallow, small Loose Wet avalanches possible on some steep sun exposed slopes, mainly during the warmest part of the day. Watch for warning signs like new roller balls, pinwheels, and natural Loose Wet avalanches that indicate increasing hazard. Even small Loose Wet avalanches may carry you into terrain with high consequences such as over cliffs or into gullies. 

Snowpack Discussion

Temperatures have warmed over the last several days with mild daytime temperatures. Only shallow recent snowfall of 1-2 inches have accumulated, mostly Thursday with little to no snow earlier this week.  This has allowed for snowpack settlement and the development of a strengthening melt freeze crust. Older Wind Slabs have now stabilized. 

There has been recent slab avalanches, likely released over the past few days on a weak layer above a strong melt-freeze crust buried about 1.5 ft on lee slopes above Hurricane Ridge. This layer has been tracked over the past few weeks but has now produced at least two slab avalanches, each with crown depths about 1.5 ft and propagating over 100 ft wide on NE aspects between 5200-5400 ft. 

There are no other significant layers of concern in the snowpack at this time.

Observations

On Thursday, 3/29 NWAC professional observer, Matt Schonwald saw evidence of two recent slab avalanches releasing on steep convexities on NE aspects between 5200-5400 ft. These avalanches released on a weak layer, poorly bonded to a hard crust. Several snowpack tests on this layer confirmed the propensity for avalanches to propagate.

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.

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.