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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, April 24th, 2015 - 7:00AM
Expires
Sat, April 25th, 2015 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Today will start with a generally LOW avalanche danger and rise to MODERATE  as the snow surface begins to soften with daytime warming. Wet loose avalanches releasing naturally or triggered by a person will again be the main concern on East, South and West aspects at all elevations. These can be quite large in steep sustained terrain. Also, keep in mind lingering wind slabs can re-activate with warming in the upper elevations on all aspects.

Fri, April 24th, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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. 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
  • 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

Yesterday’s sunshine, calm winds and rapidly warming daytime temperatures triggered numerous wet loose avalanches on predominantly South and West aspects. We should expect a similar pattern today as partly cloudy skies and light winds are forecast. Yep, we are in a classic springtime melt-freeze cycle with a generally solid snowpack in the morning giving way to wet loose avalanches later in the day. The rule of thumb is, once the surface snow/crust becomes saturated to your boot tops (with skis/boards off) it’s time to head to a cooler aspect. There is still plenty of cold and dry snow, but it is at the upper elevations on Northerly aspects.

*If the winds stay light today, don’t be fooled if there is some cloud cover; thin clouds can create a type of ‘green house’ effect and warm all aspects, including North.

Photo on the left is from the North side of Tincan where a very large wet slide occurred sometime in the past 3 days. This slide is off a Northerly aspect and debris was reported to be 10-15′ deep. (Photo credit: Hunter McConnel). Photo on the Right are your classic wet loose avalanches in steep South facing terrain (Photo: Graham Predeger).
  

Avalanche Problem 2
  • 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

We know of one large slab avalanche, possibly a large wind slab, that released naturally in the past 48 hours. This avalanche (pictured below) is on a Westerly aspect across Turnagain Arm from around Seward Highway’s Mile Post 94, just East of Mount Alpenglow. The take home here is, although unlikely, triggering an old slab is not out of the question with our transitioning snowpack from winter to summer. 

Fresh wind slabs may build at the upper elevations later today if we see an increase in South and East winds. Although there is plenty of loose snow available for transport, these are expected to be isolated and shallow and confined to Northerly aspects.

*The avalanche pictured is a reminder that even during times of low danger, we need to keep our safe travel habits alive and not become complacent; the main two being, exposing only one person a time and watching our buddies.

Recent slab off a West aspect across Turnagain Arm. (Photo credit: Graham Predeger)

Weather
Fri, April 24th, 2015

It was a brilliant day in the backcountry yesterday with sunny skies and light and variable winds. Temperatures at the upper elevations reached 32F and at 1,000′ the low 40’s F.

Another nice day is on tap today, however temperatures are not expected to get quite that warm (upper 20’s on the ridgetops and upper 30’s at 1,000′). Winds should pick up slightly to the 10mph zone from the East and South. We could see some high clouds filter in and out associated with a large low pressure over the Aleutians.

For the weekend, it looks like partly cloudy skies continue with light to moderate East winds. The low pressure over the Aleutians looks to track to our South with the moisture missing Southcentral.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37   0   0   72  
Summit Lake (1400′) 30   0   0   14  
Alyeska Mid (1700′) 36   0   0   45  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 29   VAR   4   14  
Seattle Ridge (2400′) 28   n/a   8   22  
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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.