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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, April 4th, 2013 - 7:00AM
Expires
Fri, April 5th, 2013 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

Today will be a similar pattern as to what we’ve seen the last few days with warm daytime temperatures and direct sun contributing to a spike in the hazard late in the day.   The avalanche danger will start LOW this morning and increase to MODERATE on sun affected slopes as the afternoon wears on.   Furthermore, it will be prudent to avoid cornices today like the plague; this includes spending time in their looming shadows.

Special Announcements

Are you going to Arctic Man this year?   Join Alaska Mining and Diving Supply, the Friends Group and CNFAIC Forecaster Graham Predeger for a free “Hoodoo Mountain Snowpack and Avalanche Assessment” field workshop on Wednesday afternoon!   Meet at the AMDS tent at 2PM for a fun and informative afternoon of snowpits and POW as we try and wrap our heads around what the primary avalanche concerns will be for the week!   Contact Graham at graham@chugachavalanche.org for more information.

Thu, April 4th, 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
  • 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

Wet avalanches will again be our primary concern today likely becoming active on southerly slopes late in the day as the snowpack continues to absorb solar radiation, subsequently weakening the bonds between individual grains.  This is the “melt” process of the melt-freeze cycle.  Pay attention to the snow surface throughout the day.  Indicators of the avalanche danger rising will come in the form of point releases, roller balls on steep slopes and a boot penetration above your knees.  If you are seeing any of these signs it’ll be a good idea to avoid steep slopes on the south end of the compass, as these are all indicators of our snowpack losing strength. 

As seen in this photo below, sun induced slabs are also of concern this week.  These have been relegated to the upper most layer of our snowpack with no signs of stepping down into older snow, though a potential for wide propagation exists.

Avalanche Problem 2
  • Cornice
    Cornice
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

Today will be the 5th day in a row of a melt-freeze cycle with cornices undergoing the same diurnal changes as the snowpack.  Once the day heats up and individual snow bonds weaken, cornices will be more likely to fail spontaneously.  As was the case on Goat Mountain (Girdwood Valley) Tuesday, cornice failure may trigger a slab avalanche once it fails, neither of which you want to be involved with today.  Continue to use good judgment around cornices and avoid prolonged exposure, specifically late in the day. 

 

 

ADDITIONAL CONCERNS

There is still some uncertainty on northerly slopes where shallow wind slabs have been found to be reactive on buried surface hoar and near surface facets.  The good news is that our mid-pack is showing respectable signs of strength and wind slabs from last weeks storm don’t appear to be stepping down into deeper layers.

Weather
Thu, April 4th, 2013

Yesterday was another beautiful spring day in the backcountry.   SE winds in the teens and low 20’s kept the snow surface cool enough that we didn’t experience much avalanche activity.  

Today looks to be another warm day on tap with temperatures reaching mid-40’s at 1000 feet and winds very light out of the east.   Direct sun and less wind than yesterday will contribute to a rise in the avalanche danger this afternoon.   No precipitation is expected to fall today.

Temps will again fall overnight though they may not rebound quite as high as we’ve seen this week as a colder air mass begins to move into our area from northwestern Canada.


Kevin will issue the next advisory on Friday, April 5th.  

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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.