Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, February 21st 2015 7:00 am by John Fitzgerald
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger will start out at CONSIDERABLE and climb to HIGH in the Alpine by the end of the day.  The same progression will occur at the Treeline elevations moving from MODERATE to CONSIDERABLE by the evening.  The danger will be MODERATE below treeline.  Avalanches occurring in the higher elevations have the potential to run through multiple elevation bands today.

New snow and wind will create slabs up to 1’ deep in the upper elevations.  These slabs on their own will be enough to injure or bury a person.  The potential also exists for these newer slabs to step down into deeper weak layers, creating the potential for large avalanches.

Travel in or below avalanche terrain is not recommended today.

 Show the Complete North American Avalanche Danger Scale
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1

A modest amount of snow combined with winds will add stress to a snowpack that is hanging in the balance.  Fresh slabs up to 1’ thick on steep leeward slopes in the Alpine have the potential to release on their own.  Given the warm temps and high level of moisture in the new snow, many of these slabs will “stick” well to underlying surfaces.  Because of this it will take steeper slopes, over 35 degrees, to get slabs to move.  This concern will be more pronounced where winds are actively loading slopes.  These slabs also have the potential to step down into deeper layers in the snowpack.  

Snow that feels stiff, sounds hollow or produces shooting cracks and is connected to steeper terrain should be avoided today.

Avalanche Problem 2

A layer of weak faceted snow sits anywhere from 6” to 3’ below the surface.  This layer continues to be reactive in tests.  Average slab depths in the Alpine prior to this current storm were 2 feet.  Adding into the equation another slab makes this avalanche concern a higher priority in terms of consequences.  While it may be more difficult for humans to trigger a slab at this depth, the potential still exists.  This layer has also shown high propagation potential.  Avalanches occuring at this layer have the potential to pull out across large areas.

Because of this potential travel in avalanche terrain is not recommended today.

Additional Concern

Rain will weaken the snow surface today.  Should the rain/snow line creep above the 2,000’ level, there is potential for wet slab avalanche activity.  Below 2,000’ wet loose avalanches are possible in steep terrain.  Volume will be generally low.  Pay attention to the terrain below you, as terrain traps such as cliffs, gullies, and trees will increase the consequences of being caught in relatively small wet loose avalanches today.

Mountain Weather

Yesterday saw the beginning of a surge of moisture spreading across the forecast area.  Warm, wet and windy was the general theme.  Ridgetop temperatures were in the high 20s F and low 40s F at sea level.  Precipitation began by late morning with the rain/snow line hovering around the 2,000’ level.  Below this line rain fell with the Girdwood Valley receiving .5” and Turnagain Pass picking up .3”.  Snowfall amounts above the rain/snow line range from 3-5”.  Ridgetop winds have been moderate with Seattle Ridge blowing in the 30-40 mph range.  

Southerly flow will continue to impact the area today with more of the same.  Precipitation amounts will be around .5” of H20, with snowfall in the 3-5” range.  The rain/snow line will be around the 2,000’ mark.  Winds will be out of the East at 25-35 mph.  Temperatures will climb to 40 F at 1,000’.

The extended outlook is showing a continuation of this warm, wet and windy pattern through the weekend.  Intensity will diminish by tonight, but showery conditions will persist through Sunday and into the early part of next week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 33 2/rain .2 43
Summit Lake (1400') 37 rain .1 8
Alyeska Mid (1700') 35 rain .5 24


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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 27 n/a n/a n/a
Seattle Ridge(2400') 29 n/a 30 67

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: Oct 05, 2019 )

Glacier District
Johnson Pass: ClosedClosed
Placer River: ClosedClosed
Skookum Drainage: ClosedClosed
Turnagain Pass: ClosedClosed
Twentymile: ClosedClosed
Seward District
Carter Lake: ClosedClosed
Lost Lake Trail: ClosedClosed
Primrose Trail: ClosedClosed
Resurrection Pass Trail: ClosedClosed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor: ClosedClosed
South Fork Snow River Corridor: ClosedClosed
Summit Lake: ClosedClosed

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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.

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