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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, January 3rd, 2016 - 7:00AM
Expires
Mon, January 4th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Over the last two days 3 feet of new snow and strong winds have rapidly loaded the mountains surrounding Turnagain Pass and created a HIGH avalanche danger in the Alpine zones (above 2,500′). CONSIDERABLE avalanche danger exists at Treeline (1,000′-2,500′) where triggering a wind slab 2-6′ thick is possible today on steep wind-loaded slopes. Sticking to mellow terrain (off and out from under slopes 35 degrees and steeper) and avoiding avalanche terrain is recommended. In the Treeline zones, careful snowpack assessment and conservative route-finding will be necessary. A MODERATE danger exists in the runout zones below 1,000′ where debris from an avalanche above could reach.    

*At Summit Lake 2 feet of new snow has created dangerous avalanche conditions. Yesterday a snowboarder triggered a 3′ slab on Tenderfoot, and luckily was not buried or injured. Don’t forget to check the weekly summary for Summit Lake (on the Kenai). This summary is produced on Saturday mornings at 7am.

Special Announcements

We are sad to report an avalanche fatality occurred yesterday in Hatcher Pass involving one person on a snowmachine on the Willow side of the Pass. Right now information is limited; check out Hatcher Pass Avalanche Center website and read the most recent article HERE on Alaska Dispatch News.  

OUTSIDE OF CNFAIC ADVISORY ZONE:

*Over the weekend natural and human triggered avalanches have occurred near Anchorage and Eagle River in the Front Range. Strong winds and snowfall are creating dangerous avalanche conditions throughout the region. Keep in mind summer trails can pass through avalanche paths such as the Flattop trail, where an avalanche occured on Friday. Check out several recent Front Range observations HERE.

Sun, January 3rd, 2016
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
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. 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

A strong Southerly flow will continue to bring us showery conditions today; 3-5” of new snow is expected. Easterly ridgetop winds 20-30mph will continue to transport snow in the upper elevations and load leeward aspects. This is in addition to 28”of new snow that has fallen in the last two days, a total of almost 9’ of snow since Christmas. Rain/snow line has fluctuated between 1500’ to 800’ this weekend causing wet saturated snowpack below Treeline. Wind slabs in the new snow could be as thick as 6′ in places. 

If you are thinking of heading to Turnagain Pass today, keep in mind the ‘rapid loading’ is a Red flag and warrants extreme caution. Avoid all avalanche terrain including putting yourself under steep slopes where a natural avalanche from above could run into flat terrain.

Many different avalanches are possible today:

1) Wind slab: Triggering a wind slab 2-6’ thick is likely on steep wind loaded slopes. Winds are forecast to remain from the East in the 20mph range. If this is the case, fresh and sensitive wind slabs will remain through the day. 

2) Cornices: With such strong winds and warm snow at the ridgetops, we can expect cornices to be tender! Not only can these trigger an avalanche below, but may also trigger a slide breaking deeper in the snowpack – creating a very large avalanche. 

3) Wet loose avalanches: Rain and wet snow has saturated the snowpack below 1500’ in Turnagain (up to 2000’ in Girdwood and Portage.) This is more of a concern in areas with terrain traps and in steep channeled terrain where an avalanche from above will be impossible to escape. Cooler temps today will be helping this part of the snowpack drain.

Be aware that plow drivers are working hard to keep Turnagain Pass clear of snow. With heavy wet snowfall like yesterday many of the parking areas may not be plowed. Please try to park in places that allow the plows to continue working. 

Avalanche Problem 2
  • 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

Yesterday in Summit Lake a snowboarder triggered an avalanche on Tenderfoot in an area many perceive as safe terrain. In the last two days Summit Lake has received 2’ of new snow, which is sitting on several different layers of weak snow including buried surface hoar. Human triggered slabs 3-4’ deep are likely in the Summit Lake area today and may be triggered on slope angles less than 30°. Obvious signs like wumpfing should not be ignored.

A weak layer sitting on a hard bed surface is buried under 5’ of settled snow. Many large avalanches have been observed naturally in channeled terrain along Turnagain Arm and Portage this weekend, but due to poor visibility it is unknown if avalanches have occurred on these older layers. Periods of rain have saturated areas of the snowpack below 2000’. Several large avalanches (D3’s) were triggered yesterday morning with artillery at Alyeska. One of these large avalanches triggered a large wet slab at 1800’ likely on the Thanksgiving crust bed surface. Snow pit tests at Tincan have demonstrated good stability this weekend, but due to limited information we don’t want to make any assumptions. Buried surface hoar is also lurking in the snowpack.

The bottom line is poor structure exists in the snowpack and a 10 day loading events (snow, rain and wind) have created a high consequence avalanche problem. More time and stable weather conditions are needed before it will be safe to go into avalanche terrain. 

 

 

Weather
Sun, January 3rd, 2016

Yesterday Turnagain Pass another 8 € of new snow in addition to the 20 € the day before. Winds were in the 20’s mph gusting to into the 40’s mph. Rain was observed below 800′ in Portage and Girdwood.

Overnight winds have decreased and precipitation stopped.  Temperatures have cooled slightly dipping below 32F at the road level at Turnagain Pass.

Today Easterly ridgetop winds are expected to increase back to the 20-30 mph range. Light snow should start falling this morning into the afternoon, but only a few inches are expected. Temps look to be cooling slightly which means rain/snow line may be as low as 600′.

Heavy precipitation is expected late tonight through Monday with similar temperatures as today.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30   8    0.8 90  
Summit Lake (1400′) 31   7   0.7   32  
Alyeska Mid (1700′) 32   2  0.31 64  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   NE   20   43  
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.