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Issued
Mon, November 27th, 2017 - 7:00AM
Expires
Tue, November 28th, 2017 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

AVALANCHE DANGER IS EXPECTED TO RISE THROUGH THE WEEK. Today is the first snowfall in a series of snow events – as snow begins to pile up in the coming days, natural and human triggered avalanches will become likely.    

A quick shot of snow overnight has hit Portage and Girdwood Valley with 4-6+ inches of snow and Turnagain Pass with 1-2 inches. Another 1-3 inches is expected through the day. This new snow combined with moderate Easterly winds will increase the avalanche hazard to MODERATE for areas seeing over 4 inches. Along ridgelines and sub-ridges, watch for places the winds have formed soft sensitive wind slabs. Getting pulled down by even a small slab could have a very rough ride due to rocks and thin snow cover. Small sluffs may be seen today as well in the Portage Valley and areas favored by the storm.

*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.  

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

Mon, November 27th, 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. 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
  • 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

Normally, an article warning Alaska drivers of winter weather road condtions would be business as usual, but for those of us looking to recreate at or around Turnagain Pass, an area that has seen cold and dry conditions for November, it means it is FINALLY snowing. Temperatures have warmed, winds have increased and snow is falling. The storm is coming from the East, hitting Portage Valley with several inches of snow at sea level overnight. Girdwood Valley has seen 4-6″ of snow at the mid to upper elevations. Turnagain Pass looks to be un-favored with a mear 1-2″ so far. 

Light snowfall should continue today with an evening total of 6-8″ at the upper elevations in Girdwood Valley and 3-5″ at Turnagain Pass. The Summit Lake area may squeeze an inch or two, but this system looks to be favoring Portage Valley and North.

  

AVALANCHE CONDITIONS:

The excitement is building and powder fever is setting in. Please remember, not only is it early season, with plenty of rocks and alders to get caught in, we are also expecting increasing avalanche danger as well. 

What to watch for:
1 – How much new snow has fallen? 
2 – Has the wind blown, or blowing?
3 – Are there fresh wind slabs that crack at your feet? Stiffer snow over weaker snow?

Today’s equation is relatively simple. New snow + wind = wind slabs. If you find an area that has seen enough new snow for a wind slab, it is likely to be triggered easily on the steeper slopes (such as 35 degrees or steeper). Turnagain Pass is still VERY thin and may only see a couple inches of new snow – in this case avalanches are not expected. In the Portage and Girdwood Valleys, there looks to be enough snow to form shallow wind slabs.

As we head into this week, the main concern is weak faceted snow that will be covered up in the next few days. See Heather’s video below. Other slopes are covered with hard crusts and hard wind drifts. The weak faceted snow is our greatest concern for future snow load as it will likely inhibit the new snow from bonding. More to come on this during the week.

 

 A look at the ridgeline conditions before snowfall:

 

 

 

Weather
Mon, November 27th, 2017

Temperatures have warmed (relatively, to the 20’s and 30F), winds have increased from the East (Moderately, to the 15-25 mph) and snow is falling. The storm is coming from the East, hitting Whittier and spilling over into the Portage Valley with several inches of snow at sea level overnight. Girdwood Valley has seen similar, yet with 4-6″ of snow at the mid to upper elevations. Turnagain Pass weather stations are reporting a mear 1-2″ so far.  

Light snowfall should continue through most of the day and begin to tapper off this afternoon/evening. A total of 6-8″ is expected at the upper elevations in Girdwood Valley and 3-5″ at Turnagain Pass. The Summit Lake area may squeeze an inch or two, but this system looks to be favoring Portage Valley and North.

After this system passes, another yet stronger low pressure moves in Monday night. And another one after that. Here are the National Weather Station ‘icons’ for the grid point over Turnagian pass:

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26   1″   0.1″   7″  
Summit Lake (1400′) 15   0   0   7″  
Alyeska Mid (1700′) 20   4.5″   0.3″   11″  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  19 E    11 52  
Seattle Ridge (2400′) 22   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.
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