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Avalanche Forecast

Archived

Jan 24th, 2016–Jan 25th, 2016

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
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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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 possible along the east slopes 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 Jan 3rd and 11th and were reported throughout the Cascade east slopes. There were many reports of triggering of these layers along the east slopes through last week.

A warm front last Thursday caused light or moderate amounts of snow which changed to freezing rain or rain east of the crest.

This was followed by cooler weather and some snow. NWAC stations along the east slopes indicate up to about 4 inches for the 2 days ending this morning.

Snow and Avalanche Observations

A report here on Turns All Year for the Clara Lake area near Mission Ridge on January 17th is dramatic.

See the NWAC YouTube page here for videos from Blewett Pass and Icicle Creek for January 18th.

NCMG guides travelling adjacent to Delancey Ridge last Friday saw widespread evidence of the recent natural cycle with numerous crowns visible throughout the region. Many crowns were estimated to be about 1 meter.

NWAC pro-observer Tom Curtis was on Iron Mountain near Blewett Pass today and found the January 11th layer 35-70 cm down on NW-SE aspects in the below and near treeline bands. He found that the buried surface hoar crystals are rounding and test gave low quality results and did not indicate propagation.

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.

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.