CNFAIC LogoCNFAIC Logo

Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, March 22nd 2018 5:34 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
Previous ForecastNext Forecast
BROUGHT TO YOU BY
The Bottom Line

The avalanche danger is MODERATE above 1000'. Triggering a large, destructive slab avalanche 2-4+ feet thick is possible on all aspects above 1000' and may be remotely triggered. Watch for wind slabs along ridgelines and avoid cornices. Pay attention to afternoon warming. Evaluate snow and terrain carefully. 

Below 1000’ avalanche danger is LOW where a stout surface crust has formed on all aspects.

Check out the Summit snowpack and avalanche summary if you are headed South of Turnagain Pass.


 Show the Complete North American Avalanche Danger Scale
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.
Special Announcement

Palmer-Fishhook Road at MP 15.5 in Hatcher Pass reopened last night following an avalanche that closed the road on Monday. 

Check out the CNFAIC observations page for details about the avalanche activity that has occurred over the past week region-wide, from Hatcher Pass all the way South to Lost Lake near Seward HERE. 


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

A skier or snowmachiner triggering a deep slab avalanche 2-4+ feet thick remains a very real and scary possibility.  Strong Northwest winds over the last three days have been loading a variety of aspects and scouring ridge lines. This wind direction can funnel through Turnagain Pass and cause unusual loading patterns opposite of our normal Easterly storm tracks. If you’re out hunting for soft snow, be aware that dozens of large human triggered avalanches have occurred over the last 10 days across our region (Seward to Girdwood) including a large avalanche triggered remotely by a helicopter on Tuesday in Girdwood. Knowing where in the terrain a large and destructive avalanche could be triggered is a difficult question. It may be the 10th person onto the slope that finds a thin part of the snowpack (a trigger point) or it could be a person triggering a slab remotely on an adjacent slope or below. There is a lot of uncertainty around this avalanche problem due to well preserved and widespread buried surface hoar and facets under a thick, connected slab 2-4+ feet thick. This structure has been found at all elevations and on all aspects. Daily warming and radiation from the sun can make it easier to trigger in the afternoons and evenings, especially if winds are calm. 

With a deep slab problem it is important to remember no signs of instability may be present before a slope releases.  It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point.

A large avalanche was remotely triggered by a helicopter in Winner Creek near Girdwood on Tuesday. This avalanche was triggered from 1/4 of a mile away at 2500' and released on the layer of weak faceted snow on a slick crust that has been the culprit in most of the avalanches over the past week. 

 

A natural slab avalanche on a Northeast aspect of Raggedtop Peak in Girdwood at 3800' was first seen on Tuesday morning, but it's unknown when this avalanche released.

 


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Wind Slabs: Be aware of newly formed wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading from strong Northwest winds this week.  Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Look for cracking and identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. Warming from the sun can make triggering easier in the afternoon, and a wind slab could step down to older snow and create a much deeper and more dangerous avalanche.

Cornices: Cornices are large and looming and the sun and above freezing temperatures can make them more unstable. Give these an extra wide berth and limit exposure underneath them.  A cornice fall could trigger an avalanche on a slope below.

Strong NW winds moving snow around on Tincan Tuesday. 


Mountain Weather

Yesterday strong NW winds 20-50mph (recorded on Seattle Ridge) continued for the third day in a row throughout our region and were more pronounced in Gap zones like Turnagain Arm. Overnight NW winds decreased to 10-20mph. Temperatures in the upper elevations were in the teens F and temperatures at sea level reached the upper 30F’s in the afternoon and dropped into the low 20F’s overnight. Skies were clear and no precipitation was recorded. 

Today expect skies to remain clear and sunny.  Northwest winds 10-20mph are expected to shift to the SE (5-20mph) by the afternoon. Daytime temperatures may reach the mid 30F’s in the upper elevations and low 40F’s at sea level. Overnight temperatures will drop back into the teens and low 20F’s. 

Friday looks similar, but with calm winds and slightly warmer temperatures on tap. The next window for precipitation is Saturday afternoon and Sunday with scatter snow showers possible. Skies are expected to become overcast by Saturday afternoon with highs in the mid 30F’s and overnight lows in the low 20F’s. Easterly ridge top winds are expected to be light.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 24  81 
Summit Lake (1400') 22  32 
Alyeska Mid (1700') 22  76

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 13  NW  10  37 
Seattle Ridge(2400') 19  NW  20  50 

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
© 2018 Chugach National Forest Avalanche Information Center. All rights reserved.
FCNFAIC