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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, April 15th, 2013 - 7:00AM
Expires
Tue, April 16th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is LOW and will remain so in most areas throughout the day.  

The hazard is MODERATE on steep wind loaded terrain features where skiers and snowachiners will still be able to trigger shallow slabs up to a foot in depth.   The hazard will also rise to MODERATE in the latter part of the day between sea level and 1,000′ where temperatures will climb above freezing and the effects of the sun will loosen the surface snow.

Mon, April 15th, 2013
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. Dangerous avalanche conditions. 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
  • 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

The unusually cool temperatures of this last spell of clear weather has helped to preserve the snow quality in many areas.  This same weather pattern has also helped to weaken the snow in the upper foot of the snowpack.  Throwing moderate winds into the mix has helped to move around this weak snow and create pockets of wind slab.  As a result we have seen activity in the form of shallow wind slabs releasing throughout the forecast zone over the weekend. These slabs have now been sitting for a few days and will be less reactive than they have over the weekend.  Despite this, it will still be prudent to pay attention to steep rollovers and wind loaded features above treeline.

Avalanche Problem 2
  • 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

The temperatures will rise enough today in the lower elevations to require careful observation of the snow surface on sunlit slopes.  As the thermometer reading goes above freezing and the sun hits steep low elevation slopes, watch for small rollerballs, pinwheels and shallow point releases.

Additional Concern
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Loose Snow Avalanches.  Those venturing into big and steep terrain will need to manage sluff today.  Volume will be generally low and will become a greater concern in exposed terrain and above terrain traps.

Weather
Mon, April 15th, 2013

The clear and relatively cold weather of the past week warmed slightly yesterday, with temps at Sunburst reaching a high of 20.8 degrees F and averaging 17 F.   Winds calmed down (from an average in the teens in the morning) in the afternoon and have averaged 7 mph out of the northwest.   No new precip has fallen in the past 24 hours.

In the mountains today temperatures will climb into the mid 30s F at 1,000′.   Skies will remain mostly clear with potential for some clouds moving in late in the day.   Winds will be very calm at 0-5 mph out of the north and northwest.   No measurable precipitation is on the horizon for the next 24 hours.

The extended outlook is calling for continued dry conditions over the next several days.


Wendy will issue the next advisory tomorrow morning, April 16th.

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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.