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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Monday, February 20th 2017
Created: Feb 20th 5:27 am
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.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
 Show the Complete North American Avalanche Danger Scale
Special Announcement

Southern Kenai mountains; including the Seward zone (Lost Lake/Carter/Snug Harbor/etc):  Heavy precipitation, strong winds and warm temperatures last week have added several feet of new snow to these areas. Cautious route-finding is recommended as avalanche conditions may still be dangerous.

Other regions throughout Southcentral, AK continue to have heightened avalanche conditions including Chugach State Park and Hatcher Pass


The Bottom Line

There is a MODERATE avalanche danger on all aspects above 1,500' for triggering a slab avalanche 2-3' thick. The new snow from last week is still trying to bond with the old snow surface and triggering a large, and potentially very dangerous, slab is possible. Other avalanche concerns are cornice falls and glide avalanches; there is an opening glide crack on Seattle Ridge that threatens popular terrain underneath. If the sun shines today, calm winds may allow the surface to warm enough for loose snow sluffs in steep southerly terrain.

Below 1,500' there is a LOW danger where triggering an avalanche is unlikely due to a snowpack consisting of hard crusts.

*If skies clear up today and travel is possible to the upper elevations, remember cautious route-finding is recommended with this avalanche problem.


Primary Concern

It has been roughly 4 days since the Valentine's Day Storm exited the region and 6 days since the peak of the storm. Essentially, that has given the mountains some time to adjust to the new load (2-3+' of dense snow) but, since all that storm snow fell on a weak surface, instability remains. Today we will be in a "scary moderate" regime where the probability of triggering a 2-3' slab is lower, but the consequence can be high. This is the major concern for the day and is a tricky problem considering some slopes show better bonding than others.

The weak layer is a thin layer of buried surface hoar and near surface facets. It is deep enough (2-3') that in most areas digging a snowpit is the only way to assess it. Furthermore, finding a representative and safe place to dig a pit is also a challenge. Be aware that no red flags may be present (whumphing or cracking in the snow) and the pack could have a general "it seems fine to me" feel before someone finds the trigger point. Trigger points are often where the slab is thinner, near rocks or scoured areas. Also keep in mind, these slabs can break above you, release after several tracks are on a slope and be triggered remotely. 

 


Secondary Concern

Cornices that grew last week could still be teetering on the balance and could break further back than expected. If one does fall it may trigger a slab avalanche below, potentially creating a very dangerous situation. If the sun comes out, warming may increase the potential for them to break.  

Cornice hanging over steep terrain on Wolverine ridge. Note the older slab that was triggered on the looker's right last week. 

 

GLIDE AVALANCHES:

There is a new glide crack above the flats along Seattle Ridge, just looker's left of the up-track and Repeat Offender slide path. Avoid hanging out under this crack and any others you may see - these release without warning and are very destructive.

 

SUNSHINE?

Although cooler temperatures are moving in, the winds should be very light to calm today. This may allow Southerly slopes to warm enough for sun triggered loose snow avalanches in steep Southerly aspects. 


Additional Concern

At the bottom of the snowpack are various layers of facets with varying degrees of strength. In the Summit Lake zone and some areas in Girdwood Valley and Johnson Pass depth hoar has been found. Last week's storm cycle tested these layers and only a few avalanches that we know of broke in them (Girdwood Valley, Portage Valley and Summit Lake). These layers will be tough for people to trigger, but possible in shallow snowpack zones. The more likely case is where an avalanche occurring in the upper layers of the pack has the potential to step down and release the entire snowpack. If this does happen the volume will be large and could run long distances. 


Mountain Weather

Obscured skies with a few patches of broken cloud cover filled the region yesterday. Light snow flurries fell in the afternoon and evening with only a trace in most areas, the exception was Girdwood Valley that picked up 3-4+" of very low density snow. Temperatures were in the mid 20'sF below treeline and in the upper teen's F in the Alpine. Ridgetop winds were calm and with the light cloud cover created a 'greenhouse' effect that increased the temperature slightly during the day. Overnight, winds backed to the Northwest bringing in cooler temperatures with a very light flow, near 10F at the high elevations.

Washington's Birthday (President's Day), we can expect the cool Northwest flow to remain over the area with temperatures dropping to the single digits in the Alpine and the teens below treeline. Rigetops winds associated with this will be light, 5-10mph. Skies should be partly cloudy with clearing in some areas. A possible instability shower may add a trace of snow to some locations. 

Tuesday looks to be another break in weather with mostly clear skies while Wednesday a frontal system moves in with a chance for snow.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 18  trace  69 
Summit Lake (1400') 19  trace  32 
Alyeska Mid (1700') 19  3-4  0.2 67 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 12 
Seattle Ridge(2400') 15  Rimed  Rimed  Rimed 

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: Nov 18, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedOnly a few inches of snow sits at the motorized lot, not enough to open for snowmachining at this time. Updated Nov. 18, 2017
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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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