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Tue, March 28th, 2017 - 7:00AM
Wed, March 29th, 2017 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger will start at MODERATE at all elevations this morning, and will increase to CONSIDERABLE by early afternoon. The forecast is calling for 6-12 € of snow and ridge top winds as of 7am have increased into the 15-25mph range, (higher than originally forecasted.) Triggering a fresh storm slab 1-2′ thick or fast moving surface snow will be likely on slopes steeper than 35 degrees, but the size will be proportional to todays total accumulation. There is also a possibility that today’s snow could be adding stress to an older layer within the snowpack, increasing the possibility of triggering a larger slab avalanche. Also should the sun appear today be prepared for natural wet loose avalanches on solar aspects.  

Conservative decision making and cautious route finding will be essential today and keep an eye out for obovious clues like recent avalanches, whumpfing and shooting cracks.  

Headed to the Summit Lake area? Read the  Saturday Summit Summary  HERE.

Tue, March 28th, 2017
Above 2,500'
3 - Considerable
Avalanche risk
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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

A series of small low-pressure systems are circulating through the Gulf and into Prince William Sound bringing snow showers to our region. Overnight 3-6” fell between Turnagain Pass and Girdwood and another 6-12” is possible today. Its also possible that parts of our forecast zone may only see a few more inches. Unfortunately these types of weak systems make for a challenging snow forecast. Yet, as we saw last week, a system such as this one turned out to produce feet of snow in the Placer Valley. This may be the case again today and the avalanche danger will depend on how much snow falls and how much the winds build today. UPDATED: As of 7am ridgetop winds have increased into the 15-25mph range and are expected to remain elevated through mid day.

Snow surface prior to this storm consisted of surface hoar with loose faceted snow underneath on shaded aspects, and a sun crust on solar aspects (SW – SE). Both of these surfaces will be hard for any decent amount of new snow to stick to. Storm related wind slabs and loose snow avalanches will be the most likely avalanche problems and are expected to be easy to initiate. 

STORM/WIND SLABS: Today’s new snow and ridge top winds 15-25mph could form slabs 1-2′ thick. The size of these will depend on the total amount of snow and how much the wind blows. Remember that larger terrain features could produce larger slabs and if winds stay elevated above 15mph slabs could be more conected than expected. Keep slope angles below 35 degrees and avoid terrain traps like being at the bottom of gully.

DRY LOOSE SNOW AVALANCHES (SLUFFS): Today’s snow is expected to be very loose and unconsolidated making to really easy to trigger dry loose snow avalanches on steeper terrain features protected from any wind.  Expect sluff to be fast moving and if snow totals are closer to 12” they could easily be larger and run further than expected. 

WET LOOSE AVALANCHES:  If for some reason the sun pokes out and begins to warm the snow surface to the point of melting, it will be important to watch for wet loose avalanche activity on Southerly slopes. Avoiding these areas at times of melting is recommended.

Old surfaces vary depending on aspect and elevation. On Southerly slopes a sun crust is present and in some places this crust has near surface facets on top as was the case on Lips South face yesterday.



Surface hoar ranging from small (4-6mm) to very large (1-2cm) has been well documented at all elevations on W – N – E aspects. Poor bonding is expected on these surfaces.

Additional Concern
  • 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

Yesterday a skier triggering a small slab avalanche on a steep Northern chute on Orca, near Girdwood. The avalanche was actually triggered by their fast moving sluff below them, as they were stopped, letting the loose snow pass by. The slab was small, 12” deep and 20’ wide, but ran the full length of the avalanche path. This is a good reminder that some slopes harboring old slabs 1-2′ thick are sitting on weak faceted snow. These slabs are composed of last week’s storm snow and have mostly been eaten away with the cold temperatures – faceting to the point they are now a weak layer themselves. Yet, there are places where the slab is more consolidated, thus another reason to avoid steep slopes today if we see heavy snowfall.



Skier triggered slab on Northern chute of Orca, near Girdwood, yesterday. No one was caught in this avalanche. 

Tue, March 28th, 2017

Yesterday skies were partly cloudy becoming overcast by late afternoon. Light flurries were observed during the day and scattered snow showers started late evening. Temperatures  bumped up in the afternoon into the mid 20F’s and reached 30F at road level. Ridgetop winds were light, averaging 2 mph and as of 5am have bumped up slightly from the East at Sunburst and Seattle Ridge (5-10 mph gusting to 15mph.) Overnight 6 € of new snow was recorded in Girdwood and 3″ in Turngain Pass.    

Today snow showers will continue and snow totals could range from 6-12 € likely favoring the Portage, Placer and Girdwood. Intensity is expected to increase late morning and into the afternoon. There is also a possibility for the sun to pop out at times. Temperatures at lower elevations could fluctuate from 20F to low 30F’s with daily warming. Ridge top winds are expected to be in the 15-25mph from the East with gust in the 30’s mph.  

An active weather pattern is in store for Southcentral through the next week. Snow showers are in the forecast for the next two days as a series of small lows move through the Gulf. By Thursday into a Friday a deep Pacific Low will move into our region causing heavier precipitation and warming temperatures. This will likely be rain near coastal areas and snow inland.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   3    .2 63  
Summit Lake (1400′)  24 0   0   29  
Alyeska Mid (1700′) 25   6    .22  63

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  20 variable 2   15  
Seattle Ridge (2400′) 21   variable   2   17  
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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.