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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, February 23rd 2018 5:17 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
Previous Forecast
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The Bottom Line

The avalanche danger is MODERATE above 1,000' on all aspects. Triggering an isolated wind slab or a more connected persistent slab 1-2’ deep is possible today. Look for moist snow or small point releases on solar aspect where the sun could make slabs more reactive. Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche. 


 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

Dangerous avalanche conditions are anticipated in Hatcher Pass today following a foot of new snow that fell yesterday. Human triggered slab avalanches are likely today. If you see any activity please send in an observation to Hatcher Pass Avalanche Center HERE. 


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a slab avalanche 1-2+ feet deep remains possible above 1000’ due several weak layers buried within the snowpack. A layer of buried surface hoar from Jan. 21st continues to show signs of reactivity in the upper elevations, and a layer of facets over a melt-freeze crust is suspect in the mid elevation band. The slab ranges from hard to soft depending on exposure to recent winds. Speaking of wind… yesterday we had 3-4” inches of new snow combined a strong Northwest winds overnight. This wind direction can funnel through Turnagain Pass from a variety of directions causing unusual wind loading patterns. Be suspect of hard snow over soft snow that feels upside down or where the slab is fully supportable or hollow sounding. Red flags like shooting cracks or “whumpfing” may not be present before a slope releases. Evaluate the terrain for consequences and be aware of places that haven’t seen much traffic. These less traveled places are more suspect for triggering a more connected slab.

Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could 'wake up' if you find the wrong spot above 3,000' in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass. 

Left picture shows the buried surface hoar about a 1' below the surface, and the right hand picture is an example of the weak faceted snow sitting on a slick crust in the mid elevations. 


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a small isolated wind slab is possible today on steep unsupported terrain features where winds have been transporting snow. These slab will likely be hard and supportable due to strong winds overnight. A slab could release from above once committed to a steep slope. Identify smooth pillow-shaped snow and cross loaded gullies and be aware that buried weak layers are widespread throughout our region. It may be difficult to distinguish between a small isolated wind slab versus a more connected persistent slab. 

Sunshine:  It's that time of year when we need to pay attention to the sun. The sun can heat up Southerly aspects, and melt surface snow and cause small point releases in the loose new snow. This will be more of a concern if winds are calm today, which may be the case this afternoon. This heating can also cause a slab sitting on a weak layer to become more reactive. Avoid steep solar aspect if you notice the surface snow becoming moist or you see roller balls or point releases under rocks. 

 

Moderate North winds loading a Southern aspect on Tincan yesterday afternoon.   

 


Mountain Weather

A storm yesterday brought 3-4” of new snow throughout our region followed by a strong Northwest wind event. These winds started late afternoon and have continued through the morning. Gap areas like Turnagain Arm have experienced stronger winds. Seattle Ridge weather station was averaging in the 30’s mph overnight with gusts into the 60’s and 70’s. Sunburst weather station was more protected and the strongest winds were reported early this morning with gust into the 30’s mph. Ridgetop temperatures dropped from the 20F’s into the low teens (F) overnight. Sea level temps remained in the 20F’s overnight. 

Today expect clear and sunny skies most of the day. High clouds are expected by this evening as another low pressure system move into our region overnight.  Northwest winds are expected to decrease this morning remaining light from the Northwest this afternoon.  Temperatures will be in the mid 20F’s in upper elevations and may rise to low 30’s at sea level. Snow showers may start by late evening. 

Several inches of new snow are forecasted by Saturday. An active Southwest pattern will bring a period of clear skies on Sunday followed by another round of snow on Monday. Southwest flow tends to favor Cook Inlet and the Matanuska Valley for snow, but precipitation is expected across our region. Temperatures should remain near normal averaging in the 20’s to mid 30’s with daily warming. Precipitation is expected to remain as snow.

 *Center Ridge weather station has been producing erratic temperature data.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') *33  .2  65 
Summit Lake (1400')  25 .2   25
Alyeska Mid (1700') 25  .2  57 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  18 NW  10  34 
Seattle Ridge(2400') 24   NW 23  73 

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: Feb 15, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease access trail thru open gate and park trucks/ trailers along the road toward the trailhead. Please keep the turnaround (near large signboard) clear for vehicles to TURN AROUND!
Placer River: OpenOpen 2/16. Please avoid private property and AKRR job site at Luebner Lake. Cross railroad tracks if needed, do not ride down tracks, it is illegal.
Skookum Drainage: OpenOpen 2/16. Please avoid private property and AKRR job site at Luebner Lake. Cross railroad tracks if needed, do not ride down tracks, it is illegal.
Turnagain Pass: OpenPlease avoid riding on “Rookie Hill“ and other areas with exposed vegetation. Thank you!
Twentymile: Closed
Seward District
Carter Lake: OpenOpen 2/16.
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: OpenResurrection Pass trail is open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Open
South Fork Snow River Corridor: Closed
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
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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