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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, December 4th 2018 7:00 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 2500’ in the Alpine. As easterly winds increase today triggering a wind slab in steep leeward terrain will be possible. Additionally, human triggered slab avalanches 1-3’ thick remain possible due to a weak layer of snow under the Thanksgiving weekend storm snow.   


 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

New snow and wind has increased avalanche conditions in many zones outside of the Chugach National Forest. 


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Be on the lookout for wind slabs in steep unsupported terrain. Strong easterly winds on Saturday afternoon loaded leeward slopes in the Alpine. Surface conditions at upper elevations yesterday varied from wind skin to rime crust to sastrugi to wind slab. Winds are forecast to increase again today and there is still snow available for transport. Look for stiff, pillowed snow and cracking and listen for hollow, drum-like sounds. Loading patterns can be very localized and it is crucial to look for clues indicating where the snow is being distributed. 

 

Sunburst weather station wind profile from Friday afternoon to Tuesday morning

 Surface conditions on Sunburst and cross-loading on the north side of Magnum, December 3, 2018. Photo: Heather Thamm


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

In the Alpine, sitting anywhere from 1 to 3' below the snow surface, is a thin layer of weak snow (buried surface hoar/BSH). It got a good shake on Friday during the earthquake and a number of quake triggered avalanches are thought to have run on this BSH (buried November 23rd) layer.  Did that shake it up enough??? That is the hard to answer question. An observer Sunday found this layer to still be reactive in a snowpit on Sunburst right around 2500'. Yesterday at 3100' on Sunburst there were no results testing this layer but it was very easy to spot laid over in the snowpack. The concern is finding a slope with buried surface hoar that is still intact, reactive and that propagates into an avalanche. At this point obvious signs of instability may not be observed but some lingering suspicion is advised even as the likelihood decreases. As always use safe travel protocol and choose terrain with consequences in mind i.e. where is the avalanche path and where would I end up if the slope slides? 


Mountain Weather

Yesterday: Skies were partly sunny with temperatures in the low 30Fs to mid 20Fs. Winds were easterly 5-15 mph with gusts in the 30s. Overnight temperatures dropped into the mid 20Fs to high teens. 

Today: The forecast is for mostly cloudy skies with a chance of rain/snow showers with rain/snow line around 800'. Temperatures will be in the mid 30Fs to mid 20Fs depending on elevation. Winds are forecast to be easterly 20-40 mph with gusts into the 50s. 

Tomorrow: Cloudy skies and rain/snow showers are forecast to continue. Winds should decrease and temperatures will be slightly warmer. The National Weather Service long term discussion had a couple of interesting quotes this morning, "A high degree of uncertainty will make for an interesting forecast for the end of the week and into early next week. In short it looks like an active and wet period, but the details are murky due to model disagreement and inconsistency being far below normal."

 *Seattle Ridge wind sensor is rimed over. Alyeska Mid Wx Station and Summit Lake Snotel snow depth sensor are not functioning.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27  0  0 13 
Summit Lake (1400') 17  0   0  *no data
Alyeska Mid (1700') 28   0    0  *no data

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20   E  8 30 
Seattle Ridge(2400') 25 *no data  *no data  *no data 

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: Mar 22, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Open
Placer River: ClosedClosed as of 3.20.19 due to lack of snow.
Skookum Drainage: ClosedPlacer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass: Open
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Open
Lost Lake Trail: ClosedClosed as of 3/22. Unfortunately HEAVY rain over the past week has washed much of the snow off the lower stretches of this trail.
Primrose Trail: OpenPlease stay on trail to avoid resource damage through forested areas.
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: Open
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Open

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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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