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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, January 29th 2019 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

The avalanche danger remains CONSIDERABLE on slopes above 1,500'. Fresh wind slabs and cornice falls, due to strong wind and 6-12" of new snow overnight, may release naturally along ridgelines and human triggered avalanches will be likely. The new snow and wind loading may also overload and trigger much larger avalanches that break in a weak layer of buried surface hoar sitting 2-5' below the surface. Continued cautious route finding and conservative decision-making will be essential for a safe day in the mountains. 

SUMMIT LAKE / JOHNSON PASS:  Natural avalanches are possible and human triggered avalanches are likely due to strong wind, 4-6" of new snow and a poor snowpack structure. 


 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.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

New snow overnight with an additional 3-6" expected today along with strong ridgetop winds are overloading the tenuous snowpack. If you've been following along, you'll know that a weak layer of buried surface hoar sat 1-3' below the surface before this new snow. The layer was highly reactive during last weekend's clear skies and resulted in nine human triggered avalanches. Today, we will see how reactive it still is with another shot of stress by new snow and wind loading. 

Total snowfall as of 6am this morning for the past 24-hours:

  • Turnagain Pass – SNOTEL (1800’):  4" at station, 6-8" estimated above 2,500'
  • Girdwood - Alyeska Midway (1700’):  5" at station, 10-12" estimated above 2,500'
  • Portage - Bear Valley Tunnel (100’):  1.7" of rain, 16" - 2' estimated above 2,500'
  • Summit Lake - SNOTEL (1400'):  4" at station, 5-6" estimated above 2,500'

Wind loaded slopes above 1,500' are the most suspect for both naturally occurring avalanches and human triggered avalanches. Below 1,500' the snowpack is composed of mostly crusts and avalanches are unlikely. Although fresh wind slabs and cornice falls may be the most common avalanche today, the more dangerous avalanche is the one that breaks deeper in the snowpack. If you are headed into the mountains and skies clear enough for travel above treeline keep in mind:

1-  Large avalanches have the potential to occur naturally and send debris to valley floors
2-  Fresh wind slabs and cornice falls may step-down and trigger a large avalanche
3-  Sticking to lower angel slopes, less than 30 degrees, with nothing steeper above you is a way to avoid these dangerous avalanche conditions. 

 

Storm snow avalanches from last week's storm cycle in Lynx Creek Drainage (1/25). The debris in these slides covered the route into the upper portion of the valley. Additional slides like this are expected off steep ridgelines today. 

 

The thin gray line easily seen about a foot deep in the pit wall is the MLK buried surface hoar responsible for the rash of human triggered avalanches last Saturday and our worrisome weak layer being overloaded today. (Lynx Creek Drainage, 1/27/19, 2,800' north aspect)


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Ridgetop winds have been blowing strong out of the east (20-35mph) for the past 24-hours. We can expect fresh wind slabs and cornices to be forming as winds transport not only the new snow but older soft snow. Wind slabs are likely to be in the 1-2' foot deep range and easily triggered. This is also a prime condition for step-down avalanches. Meaning a fresh wind slab that triggers a deeper slab underneath. One that breaks 2-5' deeper in the pack creating a much larger and dangerous avalanche. 


Mountain Weather

Yesterday:  Overcast skies with light rain below ~500' and light snow flurries above dominated yesterday. Snowfall increased overnight with a total 24-hour accumulation of between 3-6" at mid-elevations as of 6am this morning. Ridgetop winds have been strong, averaging 20-35mph from the east with gusts to the 60's, for the past 24-hours. Temperatures have been in the upper 30's to 40F at sea level, 32F near 1,000' and in the mid 20'sF along ridgelines. 

Today:  Cloudy skies with snow falling above ~500', rain below, is expected to continue through today. The mountains should see between 3 and 6" of snow (.3 and .5" of water equivalent) today with an additional 2-3" tonight (~.25 water). Ridgetop winds are expected to remain in the 20-35mph range from the east. Temperatures look to sit in the upper 30'sF at sea level, in the low-30'sF at 1,000' and mid-20'sF along ridgetops.

Tomorrow:  The low pressure systems and associated fronts look to move north tomorrow decreasing ridgetop winds and snowfall. We could see some flurries tomorrow before skies begin to break. A return to clearer skies and cooler temperatures heads into the region for Thursday/Friday.  

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed.  We are currently working to replace it. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32   0.4 60 
Summit Lake (1400') 32    0.3  24 
Alyeska Mid (1700') 32  0.8  48 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  NE  24  62 
Seattle Ridge(2400') 28  *N/A  *N/A   *N/A  

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: Mar 22, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Open
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: Open
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Open
Lost Lake Trail: ClosedClosed as of 3/22. Unfortunately HEAVY rain over the past week has washed much of the snow off the lower stretches of this trail.
Primrose Trail: OpenPlease stay on trail to avoid resource damage through forested areas.
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: Open
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Open

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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
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