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Mon, January 4th, 2016 - 7:00AM
Tue, January 5th, 2016 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

Heavy precipitation and strong winds expected in the Eastern Turnagain Arm area today and tonight will increase the avalanche danger to HIGH at the upper elevations and CONSIDERABLE at the treeline elevations. Natural avalanches are likely and could run into snow-free zones below 1,000′ where a MODERATE danger exists. Avalanche activity today will encompass both dry slab and wet snow avalanches. These are not only expected to occur naturally, but human triggered avalanches on slopes 35 degrees or steeper are likely.

*Travel in avalanche terrain is not recommended while the storm moves through the area. Today is yet another day to stick to mellow terrain and stay out from under steep slopes and gullies. This includes avoiding trails running under slide paths such as Johnson Pass Trail and Lynx Creek drainage.

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Mon, January 4th, 2016
Above 2,500'
4 - High
Avalanche risk
3 - Considerable
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

After a brief break between storms yesterday, yet another warm ‘fire-hose’ of sub-tropical moisture will be pumping our way today. Easterly winds are just picking up this morning and should reach gale force (or up to a 10 on the Beaufort Scale) by noon on the ridgetops. Precipitation has just begun as well and we can expect 1″ of rain below 1,300′ and around a foot of snow in the Alpine (another 1″ is expected tonight with a rain/snow line dropping to ~600ft). What this all means is another day of HIGH avalanche danger in the mountains.

Avalanche issues today will be similar to those seen since Christmas Eve when this series of storms began. These are: WIND SLABS, STORM SLABS and CORNICE FALLS. Most of the activity we have seen so far has been initiated in the dry snow above treeline. Several slides have been big enough to deposit large amounts of debris at the bottom of the path. Today’s storm is just as likely to create large avalanches and until we see a true break in weather, sticking to gentle slopes and areas well away from slide paths will be key. 

Just because you are in the trees and out of the wind doesn’t mean the pack is stable; especially in the Summit Lake zone. Here the pack is shallower and harbors more weak layers under the recent storm snow. We went out to look at a snowboarder triggered avalanche from Saturday on Tenderfoot yesterday. What we found was a layer of buried surface hoar existing right around treeline (2,000-2,400′) that was responsible for this avalanche. More details on that HERE and HERE

Avalanche Problem 2
  • 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

With another spike in temperatures, rain up to 1,300′ and wet snow to 2,000′, we may see additional natural wet avalanche activity below 2,000′. Many of the gullies along the Seward Highway and Seattle Ridge have slide over the past week, wet debris can be seen in the bottom of these. Although most of these slides start as dry avalanches in the Alpine and run into wet snow on the descent, some do initiate below 2,000′ as true wet avalanches. Needless to say, steering clear of runout zones is advised.

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

Sitting under 5-7′ of settled storm snow is a layer of old faceted snow over the Thanksgiving Rain Crust. As we pile more and more load on top of this facet/crust combo, we could see very large avalanches. Some of the large avalanche activity seen during this past week may have ‘stepped-down’ into this deeper layer. And, just one more reason to let the mountains be as these storms roll through.

Mon, January 4th, 2016

Yesterday’s weather saw intermittent light snowfall above 900′ and light rain below this. Accumulation was 0-2″. Skies were overcast with a few breaks in cloud cover. Winds were moderate (averaging in the teens with gusts in the 40’smph) from an Easterly direction. Temperatures were in the mid 20’s F on the ridgetops and around 32F at 1,000′.

Overnight, temperatures have climbed to 39F at 1,000′ on Turnagain Pass (I know, yikes!) and the upper 20’s on the ridgetops. Winds are on the rise as well, averaging 40-50mph with gusts over 80mph. This is all in response to another large Pacific storm in the Gulf, which is ushering in sub-tropical moisture, and warm temperatures today.  By 6pm tonight we are expecting 1″ of rain to fall below 1,300′ and up to a foot of snow at the high elevations; another 1″ of water (10-12″ snow up high) is expected tonight but the rain line should drop to ~600 (which is good news for snow at the parking lots). Winds today will be very strong – averages in the 50’smph with gusts over 90mph.

A break in storm systems tomorrow and Wednesday may allow skies to clear a bit before yet another warm/wind/wet storm arrives on Thursday/Friday.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29   1   0.2   85  
Summit Lake (1400′) 30   0   0   30  
Alyeska Mid (1700′) 32   2    0.2  62

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  24  NE 23   80  
Seattle Ridge (2400′) 26   N/A   N/A     N/A    
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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.