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Avalanche Forecast

Archived

Jan 24th, 2016–Jan 25th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Stevens Pass.

Take time to identify features where wind loading has occurred and go around them and watch for sun effects on steep solar slopes. Conservative decision-making is also advised until the persistent slab problem can be ruled out. 

Detailed Forecast

Fair weather should be seen Monday with a slight warming trend.

Previous mostly small wind slab may linger mainly on lee north to southeast slopes. Watch for signs of firmer, hollow wind transported snow.

Some sun and warmer temperatures should make loose wet avalanches possible on steep solar slopes. Watch for wet surface snow deeper than a few inches on solar slopes and roller balls that usually precede loose wet avalanches.

We will continue to list the January 3rd and 11th persistent slab problem as unlikely in the forecast until further observations show we can confidently put the problem behind us.

 

Snowpack Discussion

Weather

Two fair weather periods earlier this month allowed surface hoar and near surface faceting to occur. These persistent weak layers were buried intact on January 3rd and 11th.

A warm front last Thursday caused heavy rain on the Washington volcanoes. Heavy snow changed to lighter freezing rain and rain in the passes. This caused an avalanche cycle and consolidation along the west slopes.

This was followed by cooler weather and some snow. NWAC stations along the west slopes indicate about 3-6 inches for the 2 days ending this morning.

Recent Observations

NWAC pro-observer Lee Lazzara was in the Canyon Creek area near Mt Baker on Saturday and noted minor wind transport. The January 11 buried surface hoar layer was seen in pits about 55-60 cm down on NW-NE slopes at about 5500 feet. The crystals were getting compressed and were rounding and only some tests with heavy loading indicated some propagation.

NWAC pro-observer Ian Nicholson was at Stevens not far above the pass on Saturday. He found moderate-hard tests in upside down snow from Thursday but did not see signs of the January 3rd or 11th layers.

NWAC pro-observer Dallas Glass was at Paradise on Saturday and found generally right side up snow and no major weak layers.

NWAC pro-observer Ian Nicholson was at Skyline Stevens Pass today and mainly found wet heavy snow at 4400 feet. At 4900 feet he found the January 3rd or 11th layer at 115 cm down but the crystals were getting compressed and hard to trigger. Limited wind transport was seen around the valley.

Problems

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.

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.