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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, March 18th, 2015 - 7:00AM
Expires
Thu, March 19th, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger for Turnagain Pass is CONSIDERABLE both in the Alpine and at Treeline. Human triggered slab avalanches up to 2′ thick will be likely in steep terrain and remotely triggered avalanches are possible. Careful snow pack evaluation and cautious route finding are essential today.

Expect snow conditions to change throughout the day and small wind slabs 4-8 € thick could be an additional concern. Today is a good day to stay on low angle terrain and avoid all steep slopes.  

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Wed, March 18th, 2015
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Up to 4 inches of new snow combined with 20-30 mph ridgetops winds from the Northeast are expected today. This will continue to make human triggered slab avalanches likely on steeper slopes.  

Two days ago a storm left 2’ of new snow blanketing all of Turnagain Pass to the roadside. This slab is sitting on a weak layer of faceted snow that exists both in the Alpine and at Treeline. Yesterday conditions were very tender and a handful of slab avalanches released naturally due to unusually warm temperatures on sun-affected aspects (East and South facing slopes.) Two separate skier triggered slabs were observed on Tincan below 2500’. One of these incidents was remotely triggered causing a large pocket 200’ wide to run about 500’ down the slope.

Today avoid all steep slopes, even small ones with terrain traps below. Remotely triggered avalanches are possible and it will be extra important to not put yourself in the run-out of a steep slope, especially if other backcountry users are in the area. Obvious signs of instability like collapsing and recent avalanche activity will be additional reminders today to keep it mellow! 

Yesterday was a classic example of why CONSIDERABLE is the most dangerous rating for humans. 2’ of fresh powder followed by a sunny warm day and multiple parties pushing slope angles into steeper terrain. The photo below is of a remotely triggered slab avalanche on a WSW aspect of Tincan. Luckily no one was caught or injured.

 

 

 

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

Fresh Windslabs

Ridgetops winds from the Northeast are expected to be moderate 20-35 mph throughout the day. Windslabs 4-8” are possible on leeward aspects of terrain features. These wind slabs are an additional reason to stay off of steeper terrain while small bursts of precipiation and wind move through Southcentral Alaska over the next two days. 

Weather
Wed, March 18th, 2015

Yesterday skies became clear and temperatures were in the mid 40’s F at lower elevations. At ridgetops temps stayed cooler, mid 20’s F and winds were light 10-20 mph from the ENE.   No new precipitation was recorded.

Overnight cloud cover kept temperatures on the warmer side, above freezing at lower elevations. Ridgetops remained in the mid 20’s F. Winds picked up along ridgetops and Sunburst was averaging mid 20’s mph from the ENE since 1am.

A low pressure centered over the Alaskan Peninsula is set up nicely to send several bursts of precipitation to Southcentral Alaska over the next two days. Expect warm temperatures, mid to high 30’s F near sea level. Rain/snow line should be near 500′. Today 4 € is expected to fall at higher elevations with an additional 2-3 € later in the evening. Ridgetop winds will be moderate 20-30 mph from the NE.

 *Wind data was only available at Seattle Ridge Wx station after 12am.    

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35   0   0   57  
Summit Lake (1400′) 31   0   0   16  
Alyeska Mid (1700′) 34   trace   .01   37  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   ENE   15   52  
Seattle Ridge (2400′) 28   *N   *11   *28  
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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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