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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, March 15th 2018 5:38 am by Graham Predeger
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There is a CONSIDERABLE avalanche danger today at all elevations. We’ve seen natural or human-triggered avalanches everyday since Monday and our snowpack structure is such that snowmachiners and skiers may trigger an avalanche from a distance or the bottom of a slope today.  Be mindful of avalanche run-out zones and what is above you.  Cautious route finding and conservative decision-making will be essential. Large slab avalanches 2-4’ thick failing naturally will also be possible if we see daytime warming ahead of this next storm.   


 Show the Complete North American Avalanche Danger Scale
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
Special Announcement

All skier and snowmachiner parking lots throughout Turnagain Pass have been plowed as of yesterday.  Thanks DOT!!


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Weak layers deeper in the snowpack appear to have been the culprit in multiple natural and human-triggered avalanches since Monday.  Yesterday a skier-triggered avalanche caught and carried 3 skiers in small terrain on Silvertip (southern Turnagain Pass) on a NE aspect around 1500’.  On Tuesday we saw a natural avalanche cycle fire off in the Placer/ Skookum zone with several small and one very large avalanche (perhaps 1-mile wide), triggered by warming temperatures and high clouds producing a greenhouse effect in the afternoon hours.  And Monday saw two remote-triggered avalanches on the periphery of Turnagain Pass (Grandview and Summit Lake) in addition to two skier-triggered avalanches on Sunburst.  With the 2-5’ of fresh snow over the weekend, persistent weak layers have inched ever closer to the tipping point.  Skiers, snowmachiners and changing (warming) weather have all proved sufficient triggers this week. 

Things to keep in mind if heading into the backcountry today:

  • Any avalanche initiated will likely be 2’+ deep and has potential to propagate in big terrain.
  • Solar radiation and warm air temperatures can quickly make the snowpack unstable this time of year. Natural avalanches will be possible
  • Avalanches are being triggered from the flats or remotely from an adjacent slope – avoid runout zones
  • Ease into steeper terrain slowly. Evaluate consequences; if the slope releases will debris pile into a terrain trap?
  • You may not see any red flags or signs of instability with a persistent slab problem before an avalanche.

Multiple natural avalanches initiated by warming on Tuesday afternoon in the Skookum/ Lubner Lake area, Placer Valley.

Skier-triggered avalanche on lower Silvertip yesterday.  More info on Observations page.  

CNFAIC intern Jessie Haffener having no trouble finding the common weak layer in many of this week's avalanches.  In this case it's about 25-30" deep on Pete's North at ~2,100'.

 


Avalanche Problem 2

Wet Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Wet loose avalanches or roller balls today are indicative of solar radiation and/ or warming temperatures affecting change on the snowpack.  These have potential to trigger larger, more dangerous slabs, particularly on southerly and easterly slopes greater than 30 degrees. 


Additional Concern

Cornice

Cornices:

Cornices have grown significantly since the March 9th storm began and deposited several feet of new snow accompanied by strong winds.  Give corniced ridges an extra wide berth and minimize time spent below as a cornice fall can trigger and propagate an avalanche on a slope below.

Roof avalanches:

This is a serious concern, particularly around Girdwood this time of year.  Be mindful of where children and pets are playing, vehicles parked and entrances to buildings in relation to loaded roofs.  Often times warming temperatures after a large storm is enough to begin seeing roofs shed snow.  When a roof avalanches, it's likely to shed the entire snowpack all at once.  


Mountain Weather

Yesterday's weather turned out to be a bit more unsettled than previously forecasted.  Temperatures hovered in the mid to low 30's from sea level to 1,000' and was just cold enough to keep precipitation as snow to sea level.  1-3" of wet snow accumulated throughout the day and winds were light from the West.

Today temperatures look to be a bit warmer reaching into the mid-30's at sea level and we may see a rain/ snow mix.  Forecasted precipitation is minimal today (trace to 1" snow above 1,000') ahead of our next weather producer that arrives in southcentral this evening.  More on that below.  Winds will start off light from the SE today and increase into the 20's and 30's mph this evening.  

Tonight and into tomorrow a fast moving storm from the Southwest will impact our area.  This looks to be a bit warmer than our last storm and will be accompanied by stronger winds thru Turnagain Arm from the SE.  By Friday night/ Saturday models show an upper level ridge building over southcentral Alaska and a partly to mostly sunny weekend on tap.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  31  1 .1  88 
Summit Lake (1400') 30   0  33
Alyeska Mid (1700')  28  2  .3  81

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20   W 12 
Seattle Ridge(2400')  25  WNW 10 

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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