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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, January 26th 2018 5:22 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

Today there is CONSIDERABLE avalanche danger above 1000' (in the Alpine and Treeline zone) where triggering a storm slab 1-2 feet deep will be likely in areas exposed to recent wind. If ridge top winds remain elevated today, natural slab avalanches and loose snow avalanches will be possible. Evaluate snow conditions as you move up in elevation and keep your terrain choices mellow, less than 30 degrees. Cautious routefinding, and conservative decision making are essential. In places protected from wind triggering a loose snow avalanche will be likely on steep features. Also don’t forget - high in the alpine above 3000’, Deep Slab avalanche (3-8+ feet) will be stubborn to trigger, but could have high consequences. 

Below Treeline (1000’) and in places protected from recent wind the avalanche danger is MODERATE where triggering a storm slab 1-2 feet deep or loose snow avalanche is possible. Be aware of runout zones, terrain traps and other people around you. 


 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
  • Tomorrow (Saturday) January 27th, 11:00 am - 12:30 pm: Join CNFAIC forecasters for a FREE hands-on and in-the-snow avalanche beacon practice!! This 1.5 hour informal rescue practice is geared for all user groups. Grab your friends and join us before hitting the hills!! Great intro or refresher! Hosted by the Anchorage Snowmobile Club!  At Turnagain Pass (motorized parking lot) – Look for the blue CNFAIC snowmachine trailer.
  • Roads and parking areas in Turnagain Pass and Portage Valley may take awhile to clear. Be courteous to plow drivers and their efforts to clear snow from these areas. 


Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

A sneaky storm overnight produced an estimated 10-20”  (0.5”-1.0” water weight) of low-density snow across our region and ridge top winds increased into the 20-40mph range last night. This snow started out with light wind and single digit temps, but temperatures suddenly bumped into the 20F’s along with a spike in Easterly winds. This means storm slabs in the alpine could range from 1-2’ deep, have an upside down quality, and could be easy to trigger. This snow fell on 5” of low density snow that was covering a widespread layer of buried surface hoar and near surface facets. Below 2000' these layers are sitting on a slick bed surface crust. Bonding along these older interfaces is expected to be poor. Triggering a storm slab could be big enough to bury a person, but will depend on how deep the snow in the area you are traveling. The deeper the new snow the bigger the consequence. Clearing skies combined with high quality skiing/riding conditions may be hard to resist. Evaluate snow conditions as you move up in elevation and avoid terrain traps and being on or underneath larger steep slopes. Triggering a storm slab could run farther and faster than expected, which is the nature of cold snow. Shooting cracks, 'whumpfing', and any avalanche activity will be obvious clues that the snow is unstable.  Be aware of other groups of people in the same area and practice safe travel protocols. 

Notice the sudden spike in temps and winds last night. This combined with an estimated 10-20" of new snow are all red flags warning signs that avalanche danger is elevated. 

Web cam at DOT weather station is one of the only views of how much snow has accumulated overnight at Turnagain Pass.  24 hr snow water equivelent was not reporting at this site this morning. 

 


Avalanche Problem 2

Dry Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

In places protected from the winds loose snow avalanches ‘sluffing’ will be likely on steep terrain features. Similar to a storm slab, this dry loose snow could run faster and farther than expected. This hazard could bury a person in a terrain trap or underneath a large slope. 


Additional Concern

Deep Persistent Slabs

Unfortunately, the snowpack structure above 3000' is composed of a hard slab (3-8 feet thick) sitting on a variety of weak layers in the mid pack (including buried surface hoar) and old November facets near the ground. Deep persistent slab avalanches remain a concern on these upper elevation slopes. Triggering a deep slab is becoming difficult, but is still possible. The most likely trigger spots are thin areas in the snow cover, often near rocks, or where the slope rolls over.  South of Turnagain Pass the snow cover is thinner, triggering a slab in this area could be more likely as well. Remember, this is a 'low probability, high consequence' situation. This issue can simply be avoided by sticking to terrain below 3000’ (which is a good portion of terrain at Turnagain) and is secondary to triggering a storm slab avalanche today. Choosing low-consequence terrain in the Alpine is recommended. 

 


Mountain Weather

Yesterday a storm brought an estimated 10-20” of snow across our region. Center Ridge weather station picked up 0.5” of water and Alyeska Midway, 0.7” water, and Portage Valley (at Bear Valley) had 1.1” of water. This storm also started light winds and single digit temperatures. Yesterday evening temperatures suddenly increased into the 20F’s and Northeasterly ridge top winds picked up into the 15-40mph range yesterday evening and overnight. 

Today ridge top winds are expected to decrease, but could range from 5-20 mph from the East. Skies could range from partly cloudy to overcast and temperatures are expected to be in the 20F’s. Scattered snow showers are expected this evening.

Snow showers are expected through Saturday morning with only a few inches of accumulation expected. Temps will be in the teens (F) and moderate to strong winds are in the forecast for the weekend. In the long term forecast there is talk of warming temps and a chance for more precipitation mid week. 

*Snow totals are estimated from the Center Ridge Weather Station. They could be deeper, but snow depth sensor was not reading depths as of 6am. 

Web cam at Bear Valley in Portage. Looks like almost a 1.5' of snow in Portage overnight. 



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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 11  *10  .5  *67
Summit Lake (1400') .3  22 
Alyeska Mid (1700') 10  12  .7  59 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') ENE  13  44 
Seattle Ridge(2400')  8 21 

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, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

Subscribe to the Turnagain Area Avalanche Advisory:

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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