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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, December 19th 2017 4:04 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 at all elevations for storm slabs with new snow and wind forecasted for today.  Additionally, a MODERATE danger exists on the high elevations slopes (above 3,000') for the possibility of a slab avalanche breaking near the ground. The most concerning areas for triggering a large avalanche are where the snowpack is shallower, such as on the South side of Turnagain Pass and toward Summit Lake as well as the Crow Pass region. 

There is no hazard below 1,000' due to lack of 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.
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.
0 NO RATING Below Treeline / Below 1,000'
Special Announcement

Two CNFAIC Fireside Chats coming up this week!  Both will discuss lessons learned from past avalanche incidents. We hope to see you there!


Avalanche Problem 1

New snow falling today will land on weak surface snow and could easily become a storm slab. Surface hoar was observed to ridge-tops and the snow just below that has also begun to facet. Sluffing in the surface snow was also observed in steep terrain yesterday. Temperatures are on a rising trend today and the snow falling may be a bit upside down as warmer snow falls on colder snow. Winds are forecasted to blow into the 30s from the SE and may gust higher as there is some uncertainty about winds in the weather forecast discussion today. This could contribute to creating slabs especially in leeward terrain along ridgelines. Look for drifting and loading patterns. Give cornices a wide berth and pay attention to changing conditions. Hand pits will be a good way to assess how well the new snow is bonding to the old snow surfaces. As always practice safe travel protocols and watch for shooting cracks and whumpfing. 

Surface hoar observed along Seattle Ridge yesterday. 

 

 


Avalanche Problem 2

Observations continue to point to a stabilizing snowpack however the big question is, above 3,000' where the crusts from the warm wet storms disappear and facets under a deep hard slab may remain. Stability tests so far have been done up to 3,300' and all signs point to a strong snowpack and no reactivity in the facets. This is promising. But, we must be vigilant and conservative this week as we explore the higher elevations and gather more data. 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

Photo: Snow pit from 2820' in 1st Bowl/Main Bowl on the backside of Seattle Ridge. Stout melt-freeze crust is present in the upper snowpack from the warm/wet storms at this elevation. However, the basal facets in this pit were dry and loose. This is the type of set-up we are concerned in the upper elevations that don't have the melt-freeze crusts in the upper snowpack. 

 

 


Mountain Weather

Yesterday was clear with some patches of valley fog. There was an inversion with temperatures in the valley bottoms in the teens and temperatures at upper elevations in the 20Fs. Winds were very light. Overnight temperatures have been rising and warmer air is moving into the valley bottoms. Portage went from 20F yesteday to 33F this morning. 

Today is forecasted to be mostly cloudy with snow showers, 2-6" of snow possible. The rain/snow line may rise in the afternoon to around 500'. Temperatures will be in the low 30Fs to mid 20Fs depending on elevation. SE winds will be 15-25 mph with higher gusts into the 30s and 40s. Temperatures cool down a bit overnight and winds shift to the SW, 10-20 mph. 

Tomorrow will be partly cloudy with temperatures in the 20Fs and light winds.  Thursday looks to be clear and sunny. Another storm system is potentially on tap for the weekend but timing, precipitation and temperatures are still TBD. 

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

**Seattle Ridge has been recording intermittently. Data today is not from a full 24 hr period. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 19   0 33 
Summit Lake (1400')  9  0 10
Alyeska Mid (1700')  21  0  26

 

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') **18  **SE  **12  **25 

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

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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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