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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Saturday, December 18th 2010
Created: Dec 18th 6:39 am
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.
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.
 Show the Complete North American Avalanche Danger Scale
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The Bottom Line
Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Saturday, December 18th at 7am. This will serve as 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).

ANNOUNCEMENTS
The Lost Lake and Primrose trails are open to motorized use.

BOTTOM LINE
Today the avalanche hazard is MODERATE. Natural avalanches are unlikely, but small human triggered avalanches are possible in specific areas. Steep wind loaded pockets at upper elevations are the primary concern. Persistent weak layers are widespread through the region, but most areas lack a sufficient slab to cause avalanches.

AVALANCHE DISCUSSION
The overall danger rating is remaining steady. My own sense of caution is dropping ever so slightly on a daily basis but the continued internal weakening of the snowpack caused by faceting is preventing me from dropping the danger rating. The faceting is unlikely to produce spontaneous issues on its own and the slab that might break under a human trigger is relatively small and weak. Our main goal right now is to watch the slow faceting process and think about how its going to react in the future when we do get a heavy storm load on top. If you choose to ride on larger committing terrain this is a good time to use common sense and safe travel protocol. Expose only one person at a time, watch your partner, stop in safe spots, and have an escape plan.

Our recent snow pits have shown facet producing temperature gradients with obvious facets above and below the Thanksgiving rain crust. Weak layers around a crust can be especially dangerous because the crust can act as a slick sliding surface or support the load above before it collapses all at once on the weak layers below. Our column tests are showing moderate to hard force needed to cause failure, low propagation, and irregular failure planes. My prediction is that you really need to look hard to find the areas with built up slabs to cause avalanching right now.

Many of you may be wondering why we keep rambling on about these insidious weak layers but the reality is very few avalanches are happening. The reason lies in the structure of the snow and the related balance between stress and strength.

If you think about the ingredients for producing an unstable structure, we have two of the three pieces of the puzzle. The current structure consists of many potential weak layers over some harder layers. The puzzle piece we are lacking is a stiffer, stronger, and heavier slab on top of the junky snow. Those isolated areas near the ridges holding wind deposited pillows have proven reactive but they are only found in small pockets. When we do get a significant snowfall it will bring that final piece of the puzzle. A hard, fast storm deposit will build the dangerous slab and create stress on top of the weak layers. If we keep getting small amounts of snow at long intervals, which allows the snowpack to adjust in between, then we might not see any reaction for quite some time. Keep this in mind when our current high pressure gives way to more snow.

The key here is the critical balance between the stress and strength of the snowpack. Right now strength is low, but stress is also low. Slab avalanches happen when the stress exceeds the strength of the snowpack. At some point the stress ramps up during and after a major storm. The tipping point will be reached and avalanches will happen.

CNFAIC Staff noteworthy conditions include the obvious surface hoar forming right now. We would love to hear reports of where people are finding this most recent layer. Also the glide cracks on Seattle ridge near the motorized uptrack are slowly opening up. The snow is still gliding (moving slowly at the ground interface).

Check out an encyclopedia of terms here:
www.fsavalanche.org/Encyclopedia.aspx


WEATHER ROUNDUP
The temperature inversion continues today in the Chugach and Kenai regions. The lowest temperatures at the valley floors have come up slightly since yesterday. Wind has increased a bit in the last 24 hours. Yesterday you could see wind picking up vortexes of snow at the ridge-tops and moving it around a bit. The highest recorded gust yesterday was 36mph at the Fresno ridge station. No precipitation and clear skies are expected to continue today. Temperatures at the ridge tops have come up a little to the low 20s in some places.

Lisa will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.

The NWS weather forecast for:
INCLUDING...WHITTIER...SEWARD...GIRDWOOD...MOOSE PASS
500 AM AKST SAT DEC 18 2010

...STRONG WIND THROUGH SUNDAY AFTERNOON NEAR WHITTIER...

.TODAY...PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY SUNNY.
HIGHS 10 ABOVE TO NEAR 30...COOLEST INLAND. WEST WIND 40 TO 55 MPH
NEAR WHITTIER. NORTH WIND 25 TO 35 MPH NEAR SEWARD. NORTHWEST WIND 10
TO 15 MPH ELSEWHERE.
.TONIGHT...MOSTLY CLEAR. LOWS 5 BELOW TO 5 ABOVE EXCEPT AROUND
15 NEAR SEWARD AND WHITTIER. WEST WIND 40 TO 55 MPH NEAR WHITTIER.
NORTH WIND 25 TO 35 MPH NEAR SEWARD. NORTHWEST WIND 10 TO 15 MPH
ELSEWHERE.
.SUNDAY...PARTLY CLOUDY. HIGHS 15 TO 25...COOLEST INLAND. NORTH WIND
10 TO 20 MPH. NEAR WHITTIER...WEST WIND 30 TO 45 MPH.
.SUNDAY NIGHT...PARTLY CLOUDY. LOWS 5 BELOW TO 20 ABOVE...COOLEST
INLAND. VARIABLE WIND TO 10 MPH. NEAR WHITTIER...WEST WIND 15 TO 30
MPH.
.MONDAY...PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
SUNNY. HIGHS IN THE MID TEENS TO LOWER 30S. NORTHWEST WIND 10 TO
15 MPH EXCEPT WEST 20 TO 35 MPH NEAR WHITTIER.
.MONDAY NIGHT...PARTLY CLOUDY. LOWS IN THE TEENS.
.TUESDAY THROUGH WEDNESDAY...MOSTLY CLOUDY WITH A CHANCE OF SNOW.
HIGHS IN THE TEENS. LOWS 5 TO 15 ABOVE.
.WEDNESDAY NIGHT...PARTLY CLOUDY. LOWS ZERO TO 10 ABOVE.
.THURSDAY...PARTLY CLOUDY. HIGHS IN THE TEENS.
.THURSDAY NIGHT AND FRIDAY...MOSTLY CLOUDY WITH A CHANCE OF SNOW.
LOWS ZERO TO 10 ABOVE. HIGHS 15 TO 25.

TEMPERATURE / PRECIPITATION

SEWARD 22 15 24 / 0 0 0
GIRDWOOD 14 4 19 / 0 0 0


WEATHER STATION SUMMARY for Turnagain Pass:
-3800 Sunburst Wx Station-
Temperatures in the low 20s. Wind ranging 8-16mph from the west.
-2600 Seattle Ridge Wx Station-
Current temperature 19. Wind light and variable.
-1800 Center Ridge Wx Station-
No new snow in the last week. Temperature is 5 degrees.


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: Nov 18, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedOnly a few inches of snow sits at the motorized lot, not enough to open for snowmachining at this time. Updated Nov. 18, 2017
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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
© 2017 Chugach National Forest Avalanche Information Center. All rights reserved.
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