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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Tuesday, April 11th 2017
Created: Apr 11th 5:35 am
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.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

With sunny skies and warm temperatures forecast today, the avalanche danger is expected to increase to CONSIDERABLE this afternoon above 1000’ due to daytime warming. Large and dangerous slab avalanches 2-6+ feet deep remain possible to trigger on slopes steeper than 35 degrees that have not avalanched. Daytime warming will increase the likelihood of triggering one of these monsters in the afternoon. Additionally, triggering a wet loose avalanche or cornice will also be more likely in the afternoon. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential. 

Below 1000' a MODERATE avalanche danger exists where triggering a wet avalanche will be possible during the heat of the day. Watch for changing conditions.

Hiking in Portage Valley and on summer trails around the Advisory area (including the Turnagain Arm Trail a.k.a the bike path). Avalanches occurring at the higher elevations in this last storm sent large amounts of debris into valley bottoms and covered snow-free hiking trails. Continue to avoid trails that cross under avalanche paths such as Byron Glacier or portions of the Trail of Blue Ice and Crow Pass. The Turnagain Arm Trail between Bird and Girdwood remains CLOSED for the winter.

Summit Lake: An active avalanche cycle occurred in Summit Lake last week and elevated caution is advised. Read the Saturday Summit Summary HERE and observations from the last few days HERE.


Primary Concern

It has been 5 days since the end of a 10-day storm cycle that brought 3-6' of heavy dense snow and rain to the region. This snow fell on a widespread layer of buried surface hoar and unfortunately this layer continues to inhibit good bonding between the storm snow and the old March surface. As days pass, this layer of buried surface hoar is becoming more difficult to trigger. Furthermore, the fact that is sits over 3' deep on many slopes also makes it more difficult to trigger. However, this should not lure us into thinking a slope is safe. Keep in mind thin spots in the slab, which is where an avalanche is most likely to be triggered, exist on all slopes and are tough to see and avoid - making this deep slab problem very tricky. Things to remember if heading out today:

1-  No signs of instability may exist before a large slab is triggered
2-  Slabs can be triggered remotely from below!
3-  Several tracks may be on a slope before someone finds the thin spot
4-  Daytime warming will increase chances for triggering a slab
5-  All aspects are suspect 
6-  These slabs are large and dangerous and nothing to mess with
7-  Low angle slopes continue to be your friend, with nothing steeper above you

*More details have come if from the several snowmachine triggered avalanches in the Seattle Creek drainage over the weekend. Please see the excellent write up and photos sent in to us from the close call where a snowmachiner was able to ride up and off a very large slab avalanche in Jr's Bowl
 

Large snowmachinge triggered slab avalanche in Jr's Bowl (2nd Bowl) on Saturday, April 8th. Photos, Cory Runa.

Crown was up to 10-12' thick -  very large slab near the ridgeline where winds deposited snow during the 10-day storm cycle.

 

Large avalanche that was presumably triggered by a snowmachine on either April 7th or 8th on the NW aspect of Main Bowl (1st Bowl). Photo taken by Cory Runa on April 8th. Because of it's safe and easy access, this is the avalanche that we closely investigated yesterday - flank profile and video below.

 

 

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Secondary Concern

Springtime is upon us and daytime warming below 2,000' will again soften the surface crusts at the lower elevations and on Southerly upper elevations. While the upper elevation temperatures have remained relatively steady, in the mid 20'sF, the lower elevations below 2,000' are cooling overnight to ~30F then warming into the 40-45F range. By late afternoon watch for the snow to become saturated and unsupportable, this is the sign to move to cooler aspects. Wet loose and wet slab avalanches are still possible at these lower elevations.


Additional Concern

Cornices are large and likely hanging close to their tipping point. Direct sunshine, a person, or a group of people on top these could be enough to cause one to break. They can be extremely dangerous on their own, but with our current snowpack, they could trigger a large slab avalanche below, making a big problem even bigger. Give cornices a wide berth from above and limit exposure under them from below. 


Mountain Weather

Mostly cloudy skies coupled with instability showers along with some patches of blue sky were over the region yesterday. Over the past 24 hours, ridgetop winds have been light from an Easterly direction in the 5-10mph range and only a trace an inch of new snow has fallen. Temperatures have remained in the mid 20's F along ridgetops and warmed into in the low 40'sF below 2,000'.

Today, we should see sunshine in most areas. Ridgetop winds are expected to be light, 5-10 mph, and from a Northerly direction. No measureable precipitation is expected. Temperatures should be similar to yesterday, rising to the low 40's at the lower elevations below 2,000' and remain in the mid 20's F along the ridgetops. 

A warmer air mass begins to push in overnight and beginning tomorrow, warm temperatures, sunny skies and light winds should rule the weather for the remainder of the week. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 36  trace  72 
Summit Lake (1400') 35  25 
Alyeska Mid (1700') 34  trace  0.03  67 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24  NE   10 22 
Seattle Ridge(2400') 28  SE  19 

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be 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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