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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, March 18th 2018 4:31 am by Aleph Johnston-Bloom
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is MODERATE above 1000' on all aspects and CONSIDERABLE on all aspects below 1000'. Triggering a large, dangerous slab avalanche 2-4+’ thick is possible on all aspects above 1000' and likely below 1000' due to three days above freezing in that elevation band. Pay attention to daily warming and changing snow conditions. Remote triggering is possible. Evaluate terrain consequences and practice safe travel protocol. 

Dangerous avalanche conditions also exist in Summit Lake, check out the most recent Summit snowpack and avalanche summary if you are headed South of Turnagain Pass.

 


 Show the Complete North American Avalanche Danger Scale
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
Special Announcement

CNFAIC has issued a Special Avalanche Bulletin for the weekend due to the potential for a skier or rider or snowmachiner triggering a dangerous slab avalanche. Lots of activity has occured this week region-wide from Lost Lake all the way to Girdwood and even a few reports of natural avalanches in South Fork, Eagle River.  Check out recent observations from Hatcher Pass HERE  and get the forecast at hpavalanche.org.

Roof avalanches continue to be a concern today with warm temperatures and rain, particularly around Girdwood where there is still snow on some roof tops. Be mindful of where children and pets are playing, vehicles parked and entrances to buildings in relation to loaded roofs. 


Avalanche Problem 1

Deep Persistent Slabs

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Unlikely

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Triggering a large destructive avalanche 2-4+ feet thick is the concern today. Yesterday there was no natural activity observed but there were two remote triggered avalanches reported. Notably a snowmachiner triggered a slope in Main Bowl that had tracks on it from the day before. Without much sun or a dramatic temperature rise in the forecast today triggering an avalanche maybe more stubborn to trigger but no less dangerous. "Scary Moderate" or "Spicy Moderate" are good ways to describe the conditions today, with the exception of terrain below 1000' where triggering will be likely due to no freeze for the last 3 days. Keep that in mind in choosing terrain in Placer and Portage. With a deep slab problem it is important to remember no signs of instability may be present before a slope releases, it may be the 1st or the 10th person onto the slope that finds the trigger point and slopes maybe triggered remotely. It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point. 

Large human triggered avalanches and/or natural avalanches have released daily over the past week from Seward all the way to Girdwood. Some of these avalanches have been remotely triggered while others have released after a skier or snowmachiner were well onto a slope. So far we’ve seen one ‘very large’ natural avalanche, where the crown was a mile-wide, on a NE aspect of Skookum Valley near Placer.  Most of these avalanches have occurred below 3000’, releasing on weak faceted snow on a slick crust, 2-4 feet below the surface. A lot of uncertainty remains in the Alpine where slab depths are much deeper and triggering an avalanche could be more stubborn. Widespread buried surface hoar and facets have been well documented at all elevations. Unfortunately choosing to travel in avalanche terrain with slabs this deep and persistent weak layers is like playing Russian Roulette.  You could get away with it... or have a very bad day...

Main Bowl avalanche yesterday on an East aspect. This was a remote snowmachine trigger from the flatter gentle area below avalanche. No one was caught. Photos: Brian Bird

Snowpit from Tincan yesterday. Check out the slab depth and visualize triggering an avalanche that deep....

 Avalanche activity from the past week


Avalanche Problem 2

Wet Loose

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Wet loose avalanches or roller balls today are indicative of solar radiation and/ or daily warming temperatures affecting change on the snowpack. We have been seeing this throughout the week with unusually warm temperatures. It has been above freezing for 72 hours below 1000'. A wet point release could be small to large and has the potential to trigger a much larger, more dangerous slab, particularly on steep southerly aspects. If the sun comes out this afternoon or if rain showers are more intense than forecast, be on the lookout for natural wet loose activity. Pay attention to the surface conditions and sinking in to soft wet snow. 


Additional Concern

Cornice

Cornices have grown significantly since the March 9th storm, an event that arrived with strong winds and dumped 3-4’ of new snow. Give corniced ridges an extra wide berth and minimize time spent below them. A cornice fall could trigger and propagate an avalanche on a slope below.

 


Mountain Weather

Yesterday was partly sunny with a band of valley fog in the morning and became overcast in the afternoon. Temperatures were in the 20Fs to low 30Fs at upper elevations and the 30Fs to low 40Fs at lower elevations. Winds were light and easterly. Overnight skies were cloudy and temperatures dropped slightly. 

Today will be mostly cloudy with a chance of some brief periods of clearing in the afternoon. There is a chance of snow showers today and a chance of rain showers late in the day below 500'. Winds are forecast to remain light. Temperatures will be in the 30Fs at lower elevations and 20Fs at upper elevations. 1-5"  of snow is expected overnight and with rain possible below 500'. 

Monday snow showers continue into the morning and then as a ridge of high pressure and cooler air sets up expect clearing in the afternoon. Sunshine, cooler temperatures and possibly strong winds are on tap for the beginning of the week. The pattern looks to shift back to stormy and warmer for the next weekend. Stay tuned! 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 33   0  0  84
Summit Lake (1400')  32    0  0  31
Alyeska Mid (1700')  35    0  0  77

 

RIDGETOP 24-hour data (6am - 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  24  3  11
Seattle Ridge(2400')  27  E    5  14

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).

Winter snowmachine use open/closed status and riding conditions updates

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: Apr 20, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: Open
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: Open
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: Open
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

Subscribe to the Turnagain Area Avalanche Advisory:

The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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