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Issued
Tue, February 10th, 2015 - 7:00AM
Expires
Wed, February 11th, 2015 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

A  MODERATE avalanche danger exists at the Alpine elevations (above 2,500′) for fresh wind slab avalanches. Wind slabs up to 10″ in depth may be found on leeward slopes in areas with 4-5″ or more of new snow. Additionally, sluffs will be easy to trigger on steep slopes at all elevations and could run faster than expected.

A LOW avalanche danger can be found in terrain that is sheltered from the wind and where only a few inches of snow has accumulated.  

Tue, February 10th, 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. 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

After a long three week dry spell, we finally got a fresh coat of paint yesterday with a bit more on the way today and tomorrow. Normally, we wouldn’t bat an eye at a couple inches of fluffy stuff here and an inch there – but not this season! Snowfall totals from around the region yesterday were: (keep in mind this is VERY low density snow)

  • 10″ in Portage Valley (see photo below)
  • 5″ at Turnagain Pass North side (Eddies)
  • 3-4″ at Turnagain Pass (Sunburst)
  • 1-2″ at Turnagain Pass Southern side (Johnson Pass trailhead)
  • 3″ in Girdwood Valley
  • 1″ at Summit Lake

WIND SLABS
Unfortunately, the winds picked up last night from the East and will continue to blow today in the moderate range (15-25mph). This is prime wind loading speed and slab development for areas with new snow. Slabs will be forming on very weak faceted (sugary) snow and expect them to be touchy and easy to trigger. However, they should be quite shallow and soft, only packing a real punch in areas with 4-5″ of new snow where slabs could be up to 10″ thick – these areas of course are where many of us will seek out. The best clues to watch for will be: winds actively loading slopes, stiff feeling snow and cracks shooting from your skis/board. 
 

SOFT SLABS from Warming Temperatures:
Along with the winds forming slabs, warming temperatures will also encourage the new snow to become more cohesive and ‘slabby’. In areas with over a few inches of new snow (such as Eddies Ridge), watch for shallow soft slabs, as the new snow overlies very weak snow.

Avalanche Problem 2
  • 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

With varying amounts of new snow sitting on pre-existing loose faceted snow, you can bet sluffs will be easy to trigger on slopes over 40 degrees. These will be higher volume than we have seen and fast enough to catch you if you’re not careful. At the mid-elevations where a crust sits under the loose snow, expect sluffs to be faster than in the higher elevations.

Portage Valley ice climbers:
Wind and warming temperatures could cause natural small avalanches in yesterday’s snow to flush through gullies and over climbing routes. Heads up!

Yes, it is true, 10″ of snow in the Portage Valley (photo: Graham Predeger)

Weather
Tue, February 10th, 2015

During the past 24-hours we have seen mostly overcast skies with a few flakes adding a trace of snow. Ridgetop winds have been slowly increasing from a generally Easterly direction overnight, averaging ~20mph with gusts into the 30’s.  Seattle Ridge is blowing from the South, which is uncommon for this main flow direction. Temperatures have been climbing as well and the longtime inversion is scouring out quickly – valley bottoms are ~30F while ridgetops are ~20F this morning.

Today we can expect overcast skies and light snow showers to add up to an inch or two. Winds will be the main player as they are forecast to continue in the 15-25mph range from the East. Temperatures should remain near 20F on the ridgetops and the low 30’sF at sea level and valley bottoms.

Looking forward to Wednesday and Thursday, continued light snowfall is on tap. An embedded short wave associated with a large low pressure system South of the Alaska Peninsula  should give us a couple inches each day. Warm air is also on tap… By Thursday we could see rain showers to sea level with a rain/snow line as high as 1,000′. Stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26   1   tr   33  
Summit Lake (1400′) 23   1   0.1   8
Alyeska Mid (1700′) 26   1   0.9    23

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18   E   12   33  
Seattle Ridge (2400′) 21   SW   15   34  
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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.