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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, February 15th, 2013 - 7:00AM
Expires
Sat, February 16th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is CONSIDERABLE above treeline where over a foot of new snow and winds have created dangerous slabs that will be easily triggered today.   Below treeline the hazard is MODERATE, where isolated pockets of wind slab and storm snow will be possible for skiers and snowmachines to trigger.

Special Announcements

AK DOT will be conducting avalanche hazard reduction work today on the Seward Highway between 9:15AM and 11:00AM between Girdwood and Portage (MP88-83). Motorists should expect delays up to 45 minutes. Updates can be found at 511.alaska.gov.

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Stop by the motorized lot this morning at 11AM! Join CNFAIC forecasters and Gold Level sponsor Alaska Mining and Diving Supply (local Ski-Doo dealer) for an avalanche awareness event and memorial snowmachine ride on the 5th anniversary of this fatal avalanche in Turnagain pass.
http://www.cnfaic.org/accidents/avy021508.htm

Fri, February 15th, 2013
Alpine
Above 2,500'
3 - Considerable
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
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

Intense snowfall combined with strong winds in the early part of the day yesterday have created new slabs 2-3′ in depth.  Expect these slabs to be sensitive to the weight of a person or snowmachine today.  While some time has allowed the underlying snow to adjust to this new load, there is enough new snow, especially in wind loaded terrain to warrant concern.  These slabs are large enough on their own to injure or bury a person.  At the mid elevations, there is the possibility of these slabs to step down to older layers of weak snow.  Be on the lookout for shooting cracks, collapsing/whoompfing and snow that has a hollow feel to it.  Staying off of steep rollovers, starting zones and snow that has a rounded or pillowy look will help in avoiding this problem today. 

Avalanche Problem 2
  • 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

Snowfall amounts ranged from a few inches at lower elevations to 16″ in the higher elevations in the past 24 hours.  Expect these slabs to gradually become less reactive as the day progresses.  These instabilities tend to heal quickly.  However, an additional 4 inches of snow today will keep this problem lingering through the day.  Expect storm snow to release in terrain over 35 degrees as we experienced yesterday.  This problem will be more apparent and pronounced as you gain in elevation, particularly where new snow amounts exceed 10″.

 

 

 

Additional Concerns
Persistent Slabs

A crust that formed in the latter part of January has shown up as a problem in certain areas in our region in the past week.  A thin layer of weak snow between this crust and 2-3 feet of snow is the interface that concerns us most.  This crust is most pronounced between 1,800-2,400′.  This problem is not as geographically widespread as our primary concerns.  When traveling within this elevation band today steer away from slopes over 35 degrees, as avalanches in the new snow have the potential to step down to these older layers of weak snow.  

Cornices

Cornices have significantly gained in mass over the last 24 hours.  Keep your distance from cornices today.  They will likely be sensitive to the weight of a person or snowmachine.

Weather
Fri, February 15th, 2013

The mountains around Turnagain Arm have picked up 16″ inches of snow with 1″ of water in the higher elevations over the past 24 hours.   Winds averaged 30mph out of the East in the morning yesterday and temps were moderate, averaging in the low 20s at 3,800′.   Snowfall was most intense during the late morning/early afternoon yesterday.

Lingering snow showers are continuing to put down light amounts of snow around the area.   Winds calmed down in the afternoon yesterday and are currently averaging 2mph out of the West at the Sunburst weather station.   Temps are currently 20 degrees F at ridgetops and around 32 F at sea level.

Today lingering snow showers should produce up to 2-4 inches of accumulation.   Ridgetop winds will blow out of the West at 5-20mph and temperatures at 1,000 feet will be in the high 20s.

Tomorrow we should see clearing skies as a small ridge between low pressure systems moves through the area.

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

Observations
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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.
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