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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 31st, 2015 - 7:00AM
Expires
Wed, April 1st, 2015 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is  LOW  at all elevations this morning and may rise to MODERATE  above 2,000′ with daytime warming and sunshine. Wet loose avalanches and cornice falls, both occurring naturally and human triggered will be the main concerns if this afternoon turns sunny. Otherwise, dry sluffs should be expected on steep slopes above 2,500′ that escape warming.

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Tue, March 31st, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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
  • 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

After five days of warm stormy weather deposited several feet of good ol’ Chugach Toothpaste at the upper elevations, we should see a break in cloud cover today. If this is the case, travel to the high elevations will be possible and with long days, long tours – winter is not over yet for some! We saw very little natural avalanche activity through this storm cycle. With the ‘sticky’ nature of the snow along with a lack of known persistent weak layers, the new snow is showing signs of stabilizing quickly. The human triggered avalanche activity that did occur was within the storm snow and relatively small.

All that said, it is springtime and that time of year where sunshine and daytime warming can be the main player for de-stabilizing the snowpack. Today’s concerns:

WET LOOSE AVALANCHES:
Steep slopes with a Southerly tilt, or lower elevations, in areas where the sun shines will have wet or damp loose snow avalanche potential. Expect these to occur naturally as well as be human triggered. Keep in mind, a wet or damp sluff can entrain a significant amount of snow in steep sustained terrain.

DRY LOOSE AVALANCHES:
Dry snow exists above 2,500′ and dry sluffs should be expected on shady Northerly slopes as well as Southerlies that have not yet been affected by the sun. 

DRY SLAB AVALANCHES?:
All signs point to good bonding between the storm snow and the old underlying surfaces from last week. The one exception is upper elevation Northerly slopes. These areas may harbor faceted snow under several feet of storm snow and allow for the possibility of triggering a large slab avalanche. If you are headed to high elevation shady zones, above 3,500′ generally speaking, this is something to keep in mind and watch for.

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

Cornices deserve a lot of respect right now. They have grown substantially during the past week and though some of these have fallen on their own, many are looming. Warm temperatures and solar gain can increase the likelihood for failure. Minimizing time spend underneath them as well as giving them a wide berth on ridgelines is extremely important.

Photo below: Natural cornice failure on the West Face of Pyramid – likely occurring Sunday 3/29. Note the storm slab avalanche most likely triggered by the falling cornice. 

Weather
Tue, March 31st, 2015

It was another springtime day in the backcountry yesterday with temperatures warming at 2,000′ to the upper 30’s F. Cloud cover broke just enough for some visibility, yet it was in and out before clearing up in the evening. Ridgetop winds were in the 5-10mph range from the East before decreasing and switching to the North overnight.

Today instability showers will be over our area as we are in a break between storms. We may see up to 2″ of snow and light rain below 1,000′ in some areas and sunshine in others. Ridgetop winds will remain light from the North around 5-10mph and temperatures mild, upper 30’s F at 1,000′ and mid 20’s at 4,000′.

Wednesday night and into Thursday we will see one more weak low-pressure system move through before high pressure builds for the weekend. It could be a nice weekend for a supertour.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   0    0 59  
Summit Lake (1400′) 32   0    0 10  
Alyeska Mid (1700′) 34   trace    0.02 36

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25  NE 6   22  
Seattle Ridge (2400′) 28    n/a 7   23  
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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.