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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, December 17th 2018 4:29 am by Aleph Johnston-Bloom
Previous Forecast
BROUGHT TO YOU BY
The Bottom Line

The avalanche danger is CONSIDERABLE above 1000'. Human triggered storm slab avalanches are likely on slopes 35 degrees and steeper. Watch for signs of instability: recent avalanches, cracking and collapsing (whumpfing). Additional concerns: watch your sluff in steep terrain and avoid traveling underneath glide cracks.

GIRDWOOD VALLEY: Storms have been favoring Girdwood Valley. Yesterday over a foot of snow with an inch of water weight fell adding to the snow from Friday night/Saturday morning. Expect slabs to be deeper and potentially more reactive.

SUMMIT LAKE:  There are more developed weak layers near the ground; increasing the chance a person could trigger a larger slab avalanche. Choose terrain carefully. 


 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

If you are heading to Hatcher Pass make sure to check out the Hatcher Pass Avalanche Center's Saturday forecast and the recent observations.

TOMORROW NIGHT, 6:30 pm: Avalanche Stories from Sunburst at Powder Hound Ski Shop, Girdwood – FREE. Join Chugach National Forest Avalanche Forecaster, Heather Thamm, for an evening discussion on avalanche safety and awareness. This talk will cover some basic things you need to know before going into the backcountry. Expect to hear lessons learned and stories from Sunburst in Turnagain Pass. This talk is geared towards any level of backcountry experience, novice to the seasoned Powder Hound.


Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Expect storm slabs in terrain 35 degrees and steeper today, the bigger the slope the more potential hazard. Look for signs of instability. Slabs maybe quite soft and manageable but it will be important to ease into terrain and use small test slopes to get a sense of reactivity and depth.  Yesterday's storm brought periods of heavy snow to the advisory area with observers reporting snowfall at an inch an hour in the afternoon. Storm totals were in the 6" to 1' foot range favoring Girdwood Valley. Expect deeper snow in the upper elevation terrain. Observers on Tincan and Notch Mountain reported cracking and reactive shallow storm slabs in the afternoon. The storm snow was a bit more cohesive yesterday than the snow that fell prior. Today this instability may settle fairly quickly but should be approached with caution.  Easterly winds gusting into the 30s yesterday may have also increased slab depth and slab cohesion, especially in the Alpine.

Loose snow avalanches: In areas where the snow does not act as a slab the sluffs may be quite large and pushy in steep terrain. These could knock you off your feet and carry you. Choose terrain carefully. 

 

Storm slab on Notch Mountain, 12-16-18. Photo: Andy Moderow

Slab depth in the mid-afternoon (snow continued through the night). Notch Mountain, 12-16-18. Photo: Andy Moderow

 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

We are tracking buried layers of facets and crusts that sit 1-3' under the snow surface. These layers are more prevalent in the mid-elevations (2000’ – 2700’). Snow pit data and a lack of avalanche activity has been pointing to an unlikely chance for an avalanche releasing deeper in the pack. However, observers yesterday on Sunburst were able to get propagation on weak snow near the ground at 2100'. Additional snow load especially in the Summit area could start to tip the balance. Evaluate the snowpack and terrain as you travel. The thinner the snowpack the more suspect it is. Observers keep finding spots that whumpf on facet/crust combinations reminding us not to forget about this potential avalanche hazard.


Additional Concern

Glide Avalanches

Glide cracks are beginning to open up in many places, including Sunburst's SW face under the weather stationSW face of Tincan Proper, Gold Pan area (behind Cornbiscuit/Magnum) and there was one glide avalanche in the Johnson Pass area. These cracks can release at any moment. They are not associated with human triggers and the best way to manage the hazard is to avoid being on or beneath slopes with cracks. 


Mountain Weather

Yesterday: Skies were obscured and it snowed throughout the day with periods of heavy snow in the afternoon and into the night. Temperatures were in the 20Fs. Winds were easterly 5-15 mph with gusts into the 30s. 

Today: Mostly cloudy skies and snow showers are forecast for the day. Winds will be SE 5-15mph with gusts into the 20s. Temperatures will be in the 20Fs to low 30Fs depending on elevation. 

Tomorrow: Skies will be mostly cloudy with a chance for snow, light winds and temperatures in the 20Fs. Tomorrow afternoon there is an increased chance of snow into Wednesday as a small low circulates in the Gulf. The pattern continues to be active into the weekend.  

*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 23  0.3  37 
Summit Lake (1400') 20  0.4  17 
Alyeska Mid (1700')  20   10  1.01  29 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  NE   9 35 
Seattle Ridge(2400')  24    *no data *no data   *no data

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: Dec 18, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed
Placer River: ClosedClosed
Skookum Drainage: ClosedClosed
Turnagain Pass: ClosedClosed November 21 due to inadequate snow conditions. #hopeforsnow
Twentymile: ClosedClosed
Seward District
Carter Lake: ClosedClosed
Lost Lake Trail: ClosedClosed
Primrose Trail: ClosedClosed
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
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.


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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