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Fri, March 8th, 2013 - 7:00AM
Sat, March 9th, 2013 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is CONSIDERABLE above treeline on wind loaded slopes and below cornices.   Natural avalanches are possible in the upper elevations, where expert travel skills are necessary today.   Below treeline the hazard is MODERATE where a new load of storm snow will be possible for a person or snowmachine to trigger.

Fri, March 8th, 2013
Above 2,500'
3 - Considerable
Avalanche risk
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

Strong winds accompanied with new snow have combined to create dense slabs 2-3′ in depth in many areas.  With sustained winds averaging well over 30mph across the forecast area, expect to find wind slabs on a wide variety of aspects especially in the upper elevations.  Strong winds tend to deposit snow in the form of wind slabs further down slopes than normal.  While bonding of the new snow to the old snow is generally good, rapid loading caused by high winds is enough of a factor to create unstable conditions.  Pay attention to the makeup of the snow your are traveling on; if it feels punchy or sounds hollow and you’re in steep terrain, back off. 


                                                 Additional Concerns

Storm Snow

Storm snow unaffected by wind will be more of a concern around the Girdwood Valley, where snowfall amounts are closer to a foot.  Less snow fell on Turnagain Pass and in the Placer Valley.  In general this storm started out windy and warm which allows for good bonding between the old snow surface and this newest slab.  Slopes with more than 10 inches of new snow should be treated as suspect today.

Persistent Slabs

Yesterday my partner and I found a weak layer of snow below a crust to be somewhat reactive in tests.  This interface was about 30″ below the surface and could pose a problem at mid elevations.  This is not a widespread problem but is worth keeping in mind as new snow avalanches have some potential to step down to older buried weak layers. 

Avalanche Problem 2
  • Cornice
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.
More info at Avalanche.org

Cornices have gained in mass in the past 24 hours.  Natural cornice breaks are possible today.  Give cornices plenty of room today, as they will be very sensitive to human triggers.  Cornices have the potential to trigger slab avalanches after falling and impacting slopes.  We have seen cornices to be a problem lately during and after storms.

Fri, March 8th, 2013

In the past 24 hours strong winds out of the East have averaged 43 mph with gusts as high as 110mph at the Sunburst station (3,880′).   The peak intensity of winds occurred around 8pm last night.   Winds are still blowing in the 30mph range at ridgetops this morning, which is plenty of wind to transport snow.   Snowfall amounts have varied across the forecast zone with the Girdwood Valley picking up to 14″ of new snow with 1.4″ of water, Turnagain Pass getting 8″ of snow with .6″ of water and Grandview picking up a rain snow mix with a few inches of snow and .2″ of water.   Freezing levels have hovered around the 500-1,000′ level.

Today expect another 3-6″ of new snow and winds to continue to blow in the 30 mph range out of the Southeast with gusts to 50mph. Temps at 1,000 will be around 33 degrees F.

Light snowfall will continue tonight and taper off by tomorrow.   Lingering clouds and precip will then stick around through tomorrow prior to high pressure setting in by Sunday.


Kevin will issue the next advisory tomorrow morning, March 9th.


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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.