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Archived

Avalanche Forecast

Dec 28th, 2017–Dec 29th, 2017
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

As rainfall increases and moves to higher elevations on Thursday, watch for deepening saturated surface snow and avoid consequential terrain features. 

Detailed Forecast

A second storm (Friday) on the heels of the first (Thursday), will bring significantly more precipitation and further warming than the initial system. A surface low will track across across Cape Flattery and a cold front will move across the Olympics Friday afternoon to evening. This will cause moderate SE winds shifting to SW on Thursday at Hurricane, with further warming and increasing rain at Hurricane.

The extent and size of loose wet snow avalanches at Hurricane will depend a lot on the amount on rain received there on Thursday. At higher elevations which have received more snowfall, the loose wet slides will be larger and more dangerous. Watch for initial pinwheels, surface wet snow deeper than a few inches and initial small natural loose wet avalanches that indicated and increasing loose wet avalanche danger.

A little further wind slab development may seen above treeline on Thursday. Watch for possible slightly building wind slab on a variety of aspects above treeline as winds directions shift during the storm.

Also despite all the new snow, early season hazards still exist at some lower elevation locales and especially around creek beds that are not filled in.

Snowpack Discussion

At Hurricane Ridge, the frontal system arriving Thursday brought light snow  with temperatures just below freezing, with light to occasionally moderate SW winds.

Light snow also accumulated during a series of very weak weather disturbances that traversed the area in about the past week. 

The previous significant storm and snowfall was was 12/19-12/20.

Observations

On Wednesday, a shallow loose dry avalanche on a northwest aspect in the Tunnel Path above the road ran 100 feet and knocked a skier off his feet. A pit nearby showed right-side-up snow.

A second hand report of at least one human triggered loose dry avalanche (sluff) caught a skier(s) on Sunday 12/25. No injuries were reported. 

NWAC pro observer Matt Schonwald was at Hurricane Ridge on Saturday 12/24 and reported evidence of north to east winds but no wind slab or significant layers in the upper snowpack. The snowpack structure was generally right-side with good bonds to the Thanksgiving crust.

Avalanche Problems

Loose Wet

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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.

 

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

 

Several loose wet avalanches, and lots of pinwheels and roller balls.

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1

Wind Slabs

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.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 1