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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 26th, 2014 - 7:00AM
Expires
Thu, February 27th, 2014 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE below treeline today for wet loose and wet slab avalanches.   Warming temperatures coupled with light rain will weaken the snow surface, creating the potential for dangerous wet slab avalanches up to 2′ in depth and wet loose avalanches to knock people over in steep terrain.

Above treeline the hazard is also MODERATE.   There is potential for newly formed slabs up to a foot in depth to be human triggered in steep upper elevation starting zones.   These relatively smaller slabs have the potential to pull out deeper weak layers in the snowpack and release slabs up to 3′ in depth.

Wet avalanche concerns will become more widespread into the evening hours as freezing levels climb to ridgetops.

Wed, February 26th, 2014
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose 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.
More info at Avalanche.org

Temps around the forecast area have been steadily increasing this morning.  Light rain and snow will begin to trickle into the region throughout the day.  It will be possible for people to trigger wet slab avalanches anywhere from 6 inches to 2 feet in depth on steep slopes.  Old stiff wind slabs that formed 3 days ago will become more susceptible to triggers as temperatures rise and freezing levels climb in elevation.

Wet loose avalanches are also a concern today, especially in steep terrain above terrain traps.  Slow moving wet sluffs have the potential to push people into trees, over cliffs and into gullies.  Pay attention to the snow surface.  If you or your skis, board or snowmachine is beginning to sink more than a few inches below any damp surface, it is time to head home.  Temps will continue to climb through the day and into the night.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

We continue to find weak snow between the January crust and the Feb snow.  This layer has been gaining strength over time.  It will be difficult to trigger an avalanche at this layer, but warm temps and moderate loading (in the higher elevations) will increase the chances of pulling out slabs up to 3 feet in depth.  Steep terrain over 40 degrees should be treated with suspicion today.  The most likely scenario for activating these deeper weak layers will be wet loose/slab, or storm slab avalanches moving downslope and stepping down to the weak snow above the January crust.

Additional Concern
  • Storm Slabs
    Storm 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.
More info at Avalanche.org

In the higher elevations new snow and strong Easterly winds will build new slabs that will be sensitive to the weight of a person or snowmachine later in the day.  Slab depths will start out small and become greater by evening.  Slabs up to a foot in depth are possible by the end of the day in leeward upper elevation (above 3,000’) starting zones.   Given the warm nature of this storm, expect these slabs to “stick on” to the old snow surface relatively well.  These slabs will be most sensitive as they are forming.

Weather
Wed, February 26th, 2014

In the past 24 hours temperatures have been on a steady increase.   Ridegtop temps have been climbing towards the freezing mark, with Seattle Ridge reading 32 F at 4 am this morning.   Sunburst weather station at 3,812′ has averaged 25 degrees F.   There has been a marked uptick in winds this morning as well, with Sunburst reporting 48mph average at 4am.   24 hour average at this station was 17mph with a max gust of 67 mph.  

Today expect a warm and wet day.   Precipitation will start this morning and will initially be in the form of snow above 2,400′.   Temperatures at 1,000′ will reach 40 degrees F.   Rain/snow line should hover around 2,000′ and gradually climb through the day.   We can expect to see up to 5 € of new snow in the higher elevations with rain in the lower elevations.   Rain and snow will continue into the nighttime hours with freezing levels climbing above ridegtop level, in the 4,000′ range.

The long term outlook is complex.   Models are struggling to depict an consistent look into the weather beyond tomorrow.   The good news is that the spike in temperature should be short lived.   We can expect to see temps back to normal by the end of the week.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.