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Avalanche Forecast

Archived

Jan 12th, 2014–Jan 13th, 2014

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

Regions

Stevens Pass.

The avalanche danger should tick down a notch Monday, but storm and wind slab human triggered avalanches are still likely.  Watch for cracking in the most recent storm snow and pay attention to slope aspect. 

Detailed Forecast

The steady stream of warm frontal precipitation will lift north on Monday with only light additional loading expected through the day. The exception will be the Mt. Baker area where more moderate loading is expected through the day Monday.  Look for this area to have a locally higher danger and may be updated in the AM if warranted.  Westerly winds will strong be in the alpine, but additional wind loading should also be on the decrease due less available snow for transport and warmer temperatures.  

The greatest avalanche concerns will be from storm and wind loaded slopes that have not settled.  A Considerable Danger will be in effect on Monday at all levels: Natural slides seem unlikely Monday, but human triggered slides on wind loaded slopes releasing withing the new storm snow are much more probable. Sunday's reports indicate that deeper slides releasing down to older crust layers are possible...with perhaps a cornice fall as the right size trigger. Continue to choose your terrain and aspect wisely! 

Wet-loose avalanches are possible mainly below 4000-4500 feet where above freezing temperatures and light rain may cause pin-wheeling and loose wet slides. 

 

Snowpack Discussion

The first significant storm cycle of 2014, and more recently in the last 3 weeks, is coming to a close with some impressive numbers. With the first and weakest system arriving on Tuesday and carrying through Sunday afternoon, approximate amounts of water at NWAC stations are; 3-4 inches at Hurricane Ridge and Crystal, 6-8 in. from Snoqualmie to Mt. Baker, White Pass around 5 inches and Paradise closer to 7 inches.  In the last 24-36 hours, 1 to 2.5 feet of snow were reported with the highest snow totals from Paradise, White Pass and Green Valley (Crystal).  The NWAC station at Paradise on Mt. Rainier became the first station this season to cross the 100 inch snowdepth threshold...finally!   

Early on in the storm cycle an overall cooling trend Wednesday through Thursday helped new snow bond well to older crusted surfaces and built mostly favorable new snow profiles.  An occluded front crossed the Northwest late Thursday producing light amounts of dense snow.  While avalanche patrol at the resorts reported generally shallow soft slab releases with control, Mt. Baker seemed to an local area of backcountry instability Friday - a size 2 soft slab avalanche, skier triggered, on a south facing slope of Table Mountain was reported and was believed to release on a sun crust formed from last the weekend. 

During a wet, warm and windy Friday night, rain crept up to about 4500' in the north, 5000-5500' in the central Cascades and 6000' in the south, a cold front came through Saturday morning, dropping snow levels down to around 3000-3500' Saturday.  Mt. Baker pro patrol reported natural releases on Shuskan Arm and Mt. Herman with the Shuskan Arm slide estimated size D3 down to a recently buried crust...although poor visibility limited details. Heavy showers and strong west winds mainly above treeline continued Saturday night along with a cooling trend.  Heavy loading and a slow warming trend continued through the day Sunday, with rain mixing in mid-day up to around 3000 feet. Most ski areas reported loose snow releases within new storm snow with larger soft slab releases of 2-3 ft with explosives on wind loaded slopes. In a few areas (Crystal, Alpental, White Pass), larger explosives (or in the case of White Pass, a snowcat) were able to trigger 5' slabs on wind loaded slopes near or above treeline releasing down to deeper crusts. The White Pass 5' slab released on facet/crust combo near the ground from the late September snow.  They were not able to reproduce the results on similar aspects with explosives. 

An NWAC observer in the Stevens Pass area reported sensitive storm slab with shooting cracks below treeline and good wind transport on higher N thru SE slopes. The only natural releases reported today were of loose dry avalanches in the most recent storm snow.  Additional moderate snow accumulation at moderate snow levels with strong westerly winds in the alpine are expected Sunday night for the west slopes and Olympics. 

For the west slopes of the Cascades and Olympics, a generally favorable mid and lower snowpack exists, even if it well below seasonal norms, consisting of various crust layers, rounded grains, and melt-freeze crystals.  

5' crown - E aspect - 5700 feet - White Pass In Area (Photo by Chris Talbot)

Shooting cracks in Storm Snow 4800' - SE Aspect - Stevens Pass (Photo by Dallas Glass)

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.