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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, April 22nd 2017 7:00 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

Very warm temperatures overnight coupled with a warm day ahead will increase the avalanche danger to CONSIDERABLE on slopes over 35 degrees on all aspects above 1,000'. Wet snow avalanches ranging from small to very large along with cornice falls could being releasing today and activity may increase into the next several days. On slopes with wet and mushy snow, human triggered wet snow avalanches are likely. Lastly, debris could run into snow-free zones below 1,000', raising the danger to MODERATE at this elevation.

HEADS UP:  The springtime melt-down is here and the snowpack is continuing to lose strength as a whole and slide off the mountains. Extra caution is advised this weekend as avalanches could begin to release on West, East and Northerly aspects (avalanches are already releasing on Southerly aspects).


 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.
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.
Special Announcement
  • The CNFAIC will continue issuing avalanche forecasts on Saturday, Sunday, Tuesday and Thursday mornings until the end of April. We will be closing up shop on April 30th. However, we will continue to monitor and post any observations that come in all spring and summer - so please keep us, and the community, posted on any snow/avalanche information you may come across on your upcoming adventures!!
  • We have stopped issuing our Saturday Summit Summary for the 2016/17 season. Click HERE for our Springtime Avalanche tips.
  • Hiking on summer trails during the springtime warm-up (including the Byron Glacier trail, Crow Pass, etc).  Extra caution is advised for trails that cross under avalanche paths. Avalanches possible at the higher elevations could send debris over snow-free hiking trails. 

Avalanche Problem 1

After almost 2 weeks of sunny skies and high pressure, clouds and a warm East wind have moved in. The big news is how last night's cloud cover has trapped yesterday's daytime heat. This morning temperatures are 10-15 degrees F warmer than they have been during the past week and we are expecting a very limited, to no, re-freeze of the snow surface. The only thing that would help the re-freeze would be the increased winds, but they are only blowing 10-20mph and bringing in warm temperatures, so the wind may not keep the snow as cool as one would expect. That said, with a lack of re-freeze it will not take much daytime warming, or direct sunshine to initiate wet slab or wet loose avalanches.

WET SLAB, WET LOOSE, GLIDE AVALANCHES and CORNICE FALLS:
Although these are different characters of avalanches, they are all occuring together as the mountains fall apart with the springtime melt down. Widespread natural wet avalanche activity has already been seen on Southerly aspects, but the more shaded Westerly through Northeast aspects have yet to fall apart. This could happen this weekend as cloud cover has enhanced warming on all aspects. If choosing a day in the mountians this weekend be aware natural avalanches are possible and could become likely by Sunday. Things to keep in mind:

  1. Did the snowpack re-freeze overnight in your location? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
  2. Are you punching through a shallow crust into wet soggy snow? Also a sign the snowpack is weak and could avalanche.
  3. Do you see any recent avalanches (take a look at the photo below to help identify a recent vs. an old avalanche).
  4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
  5. Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down.
  6. Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

 Recent avalanche on Seattle Ridge (released Friday, April 21st)


Cloud cover over Tincan Ridge - trapping in the daytime heat overnight

 

 

*For the complete snow science geek out there - make sure and check out the Beaded Stream snow temperature array at the top of treeline on Tincan. This instrument measures ground, snow and air temperature vertically: Starting from 15cm (6") below the ground, there is a cable extending 4meters (12') upward that has a temperatures sensor every 15cm. The warmup of the whole snowpack can be seen - right now at this location (2,350' in a flat area) the pack is almost isothermal , which means all the same temperaure at 32F. This is important because it indicates the potential for natural wet avalanches to begin on shady Northerly aspects. 


Avalanche Problem 2

Although technically glide avalanches are a different beast than wet avalanches, they were lumped into the discussion above because how we deal with them now is similar to wet avalanches - simply avoidance. Avoid being under glide cracks - there are several cracks along Seattle Ridge, Tincan Ridge and many other slopes in the region. Each day we have seen 1-2 new glide releases (The photo above of Seattle Ridge being the last known glide release). The number of releases should increase with the warm weather.


Additional Concern

Upper elevation Northerly aspects should be warmer today. The cold dry snow surface could be giving way to a moist and wet snow surface, if it didn't already overnight. With the added warmth of the pack in these shaded zones, increased stress on underlying weak layers will be occurring. There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6' deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. As the snowpack warms up, these weak layers could re-activate and triggering a large slab avalanche is possible. This is a low probability, high consequence problem.

Keep these points in mind:  

  • It will take someone hitting a 'thin spot' in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall
  • There may be no signs of instability before the slope breaks
  • Several tracks may be on a slope before it releases
  • Stability tests may not produce any notable results

Mountain Weather

Cloudy skies (yes, cloudy for the first time in practically 2 weeks!) were over the region yesterday. Winds moved in with the clouds and over the past 24-hours ridgetops have been blowing 10-20mph with gusts in the 30'smph from the East. Temperatures warmed up to 50F at sea level, ~45F at 2,000' and 30-35F along ridgetops yesterday. Overnight only a slight drop in temperature has been seen and all elevations.

Expect a cloudy, breezy and warm day today as we are on the Northern edge of a large trough digging in the Gulf to our South. Ridgetop winds should remain in the 10-20mph from the East while temperatures continue to be near 50F in the parking lots and 30-35F along ridgetops. There is a chance for a rain drop or two tonight, but most of the precipitation will be to the South near Seward.

For Sunday, we could see light rain in places as the frontal boundary associated with the Gulf trough sends some moisture our way. In general however, the forecast is for cloudy skies, warm temperatures and breezy winds. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 42  60 
Summit Lake (1400') 41  19 
Alyeska Mid (1700') 40  54 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 30 NE  38  16 
Seattle Ridge(2400') 33  SE  30  13 

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, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of 4.3.19
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: ClosedClosed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Closed
Lost Lake Trail: ClosedClosed as of 3.22.19 due to lack of snow
Primrose Trail: ClosedClosed as of 4.3.19 due to lack of snow
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClose as of 5.1.2019
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
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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