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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, December 20th 2017 4:33 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

A  MODERATE avalanche danger exists in the Alpine. Fresh wind slabs are possible in leeward terrain.  Additionally, on the high elevations slopes (above 3,000') the possibility of a deep slab avalanche breaking near the ground remains a concern. Areas where the snowpack is shallower, such as on the South side of Turnagain Pass, towards Summit Lake and the Crow Pass region are the most suspect. 

The avalanche danger below 2500' is LOW where the snowpack is predominately thick layers of melt-freeze crust and triggering an avalanche is unlikely. 

There is no hazard below 1,000' due to lack of snow.

*Please remember your safe travel practices! This includes, exposing one person at a time in avalanche terrain, watching your partners, being rescue ready and having an escape route planned.


 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.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
0 NO RATING Below Treeline / Below 1,000'
Special Announcement

CNFAIC Fireside Chat: Avalanche Lessons Learned from Last Season. Thursday, December 21st at Powder Hound Ski Shop in Girdwood, 6:30-8 pm with Aleph Johnston-Bloom. We hope to see you there!


Avalanche Problem 1

Yesterday 3-5" inches of snow fell at upper elevations and winds were southeasterly, 15-25 mph gusting into the 30s. Winds shifted to the west in the evening. Observers reported pockets of reactive wind affected snow in leeward terrain. Today wind slabs are possible on steep wind loaded slopes. Look for drifting, cracking and pay attention to stiff snow under foot.  Even a small wind slab can be very dangerous in high consequence terrain.  In addition, give cornices a wide berth. They have been growing with each new snow and loading event. 

 

 

Cornices building and the leeward slopes of Hippy Bowl on Tincan. Photo: Sam Galoob, December 16th. 


Avalanche Problem 2

It has now been a week since the widespread natural avalanche cycle that was initiated by the warm wet storms ended. We have had no reports of human triggered avalanches since December 6th. We still do not have much snowpack data from above 3,300' this season. What we do know is that the snowpack depth is variable and that there were large natural avalanches in upper elevation terrain during the storms in the first two weeks of December. The concern is that on slopes that did not slide in the Alpine, there is still weak snow underneath all that storm snow and that a deep slab avalanche could be triggered if you found the wrong spot. If you venture out into the higher elevations today there are a few things to keep in mind:

    - Triggering a dangerous deep slab avalanche is still possible above 3,000' 
    - Shallow snowpack areas are most concerning (more trigger points and possibly more reactive facets). For example: the South end of Turnagain Pass, Crow Pass and Summit Lake
    - No red flags are likely to be present to indicate an unstable snowpack. It might not be the first person on the slope that triggers the avalanche. It could be the 10th. That is why deep slabs are so spooky. 

The bottom line is that we need more data on the snowpack structure above 3500' to rule out deep slab avalanches. This picture shows the basal structure we are concerned may still be lurking under feet of snow at upper elevations. 

 


Mountain Weather

Yesterday was cloudy and there were snow showers on and off throughout the day. 3-5" fell at upper elevations. There was brief sleet/drizzle later in the day below 500'. Winds were easterly during the day and shifted to the west in the evening. Wind speeds averaged 15-25 mph and gusted into the 30s. Temperatures were in the low 30Fs at sea level and the low 20Fs at ridge-tops. 

Today is will be partly sunny with a slight chance of snow showers in the am. Westerly winds will be light. Temperatures will cool into the low 20Fs today and dip into the teens tonight.

Tomorrow will be sunny with temperatures in the low 20Fs and light southerly winds increasing in the late afternoon. Friday will be mostly cloudy with a chance of snow showers. The next storm system looks to impact the area over the weekend. There is some hope that it won't be too warm but there is still some uncertainty. Here are the last few sentences of the NWS discussion this morning; "Behind this low is some significant cold air, which brings a chance for snow for all portions of the forecast area before Christmas Day. Either way, the forecast looks to be messy for the weekend before a return to more seasonable weather early next week."  Let it snow, let it snow, let it snow!

* Sunburst weather station is down due to loss of battery power.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27   0 32 
Summit Lake (1400')  27 3 .3  12
Alyeska Mid (1700') 28   .3  29

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') *n/a  *n/a  *n/a  *n/a 
Seattle Ridge(2400')  22 SE-W   16  37

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: May 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
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: ClosedClosed as of 4/27
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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