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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, November 28th, 2017 - 7:00AM
Expires
Wed, November 29th, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

AVALANCHE DANGER IS EXPECTED TO RISE THROUGH THE WEEK AS CONDITIONS CHANGE

The avalanche danger is  MODERATE  on all slopes near and above treeline.  Triggering a slab avalanche 1′ thick is possible today on steep slopes that have recently been loaded by winds. New snow is falling on a variety of surfaces that it may not bond well to. Pay attention to changing conditions as more snow (and/or rain) falls, temperatures rise and winds increase.  

*Below Treeline: ICE CLIMBERS in Portage Valley: Small avalanches today, and growing in size this week, could release naturally in higher terrain, sending debris over climbing routes.  

Special Announcements

Motorized use on Turnagain Pass is closed due to insufficient snow cover.  Please see riding area status at the bottom of this page for the most up-to-date information.

Snowmachine Specific €“ Avalanche Safety and Lessons Learned at AMDS, December 5th  @ 6:30 pm – 8:00 pm | FREE  Join CNFAIC forecasters at Alaska Mining and Diving Supply for a  talk about lessons learned from past avalanche events and get your brain in gear for avalanche season.

The CNFAIC Events Calendar is filling up with avalanche education opportunities. Check it out and find a class that is right for you!  

**For Hatcher Pass avalanche conditions see  hpavalanche.org.

Tue, November 28th, 2017
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. 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
  • 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

The advisory area received a few inches of additional snow in the last 24 hours and more is on tap today and tonight. Temperatures have risen and the snowline is forecasted to rise to 1000′. Precipitation that falls today and tonight will be heavier/wetter than yesterday. Warm, wet snow over cold dry snow may form storm slabs.  New snow combined with easterly winds gusting into the 40s will add to the potential for wind slabs on leeward slopes. Steep (35+ degrees) unsupported slopes will be the most suspect for triggering new or old wind slabs.  If you do venture out today it will be important to pay attention to drifting, look for cracking and listen for hollow sounds and/or whumpfing. 

Determining whether or not new snow is bonding to old snow surfaces will be the question in the next few days. Remember this snow is falling on variety of surfaces including crust, facets, old wind effected snow or grass and rocks. Getting pulled down by even a small slab could have a very rough ride due to rocks and thin snow cover. 

If rain falls on the new snow in Portage Valley wet loose avalanches will be possible in ice climbing terrain. 

Image of the melt freeze crust covering most of the terrain above approximately 1600′. The main concern is where the crust is underneath weak faceted snow that will be covered up in the next few days.  The weak faceted snow is our greatest concern for future snow load as it will likely inhibit the new snow from bonding and the crust could be a slippery bed surface. 

 

Weather
Tue, November 28th, 2017

Yesterday light snow fell in the morning and tapered off in the afternoon. Turnagain picked up a few inches and Girdwood added another inch to what had fallen overnight.  Temperatures rose to above freezing at Center Ridge, 1880′ on Turnagain Pass. Winds were easterly gusting into the 40s.  

Today will be cloudy with another 1-4 inches of snow forecasted to fall with a chance of rain up to at least 1000′. Winds will be easterly again 10-20mph gusting into the 40s. Expect temperatures in the mid 20Fs at upper elevations to mid 30Fs at sea level.  Tonight precipitation will increase, 4-8 inches of snow possible with rain/snow mix at low elevations, and the easterly winds will continue with gusts bumping into the 50s.  

Tomorrow rain/snow showers will continue and winds should decrease in the afternoon. Temperatures will stay warm until the evening as this system moves out of the area.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33    3 .3    12
Summit Lake (1400′) 29  1  .1  7
Alyeska Mid (1700′)  31  1  .1  7  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  22 ENE   18   45  
Seattle Ridge (2400′) 25   Sensor Rimed   Sensor Rimed   Sensor Rimed  
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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.