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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Saturday, February 5th 2011
Created: Feb 5th 6:56 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.
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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, February 5th 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).

BOTTOM LINE
The avalanche hazard rating is MODERATE with pockets of CONSIDERABLE. Large natural avalanches happened during and after the recent storm. Persistent instabilities will make deep avalanches possible to trigger today.

AVALANCHE DISCUSSION
The avalanches we saw yesterday were exceptional for a number of reasons and really caught our attention. We believe in hindsight that yesterday warranted at least pockets of CONSIDERABLE danger rating and that extends into today. In specific areas human triggered avalanches will be LIKELY today.

The warm sunny weather may cause some undeserved optimism about stability this weekend. Conditions are NOT NORMAL right now. In a normal Turnagain pass year we can safely travel in steeper backcountry terrain by waiting 48 hours after a storm. This is proving to be a wrong way to approach the snowpack this year. Persistent instabilities are causing deep avalanches during each storm and remaining reactive long after the storm ends.

A couple of human triggered avalanches were reported yesterday in the Turnagain Pass region. One was visible on the Seattle ridge webcam and occurred between 1:30 and 2:30 in the afternoon. This was possibly remotely triggered by a snowmachine and was estimated at 8 feet deep. AnCNFAIC Staff reported slide was also on Seattle ridge in Triangle Bowl, 4-5 feet deep.


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Natural activity was sparse in Turnagain pass, but many large avalanches happened on the southern end around Johnson Pass, Lynx creek, and Silvertip creek as well as Summit. Some of these events showed extensive and complex propagation. The thinner snowpack in this region seems to be the most likely reason for the instabilities. Expect dangerous avalanche conditions in these zones with remote triggering, upslope propagation, and abnormal distribution. Upslope propagation means that you could trigger the slope above you from a lower angle area below.


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This avalanche is still visible today from the Johnson Pass parking lot. It is located between Lynx creek and Silvertip creek. The width is estimated at 2000 feet or more, and the propagation extended across complex steep ridges that normally isolate avalanches to one side or the CNFAIC Staff. See photo gallery for more examples from yesterday.

CNFAIC Staff more remote regions including Winner Creek, Bench Creek, and 20-mile also showed some very large avalanches during and after the storm. The avalanches weve seen have not been widespread enough to clean out entire zones. This winter is producing an uneven patchwork of areas that have slid. The spotty distribution is one of the more disturbing characters of the recent avalanche cycles, which could mean areas that didnt slide naturally are teetering on the balance and waiting for the right trigger. We got reports of hair-trigger instabilities in the Chugach Front Range and Eagle river also.

Likely trigger points through Turnagain pass are shallow areas near rock outcrops (which could be slightly buried and not visible). In the shallower snowpack on the southern end of Turnagain to Summit, Snug Harbor, and Carter Lake the likelihood of triggering an avalanche will be higher. Avoiding complex steep terrain is a prudent decision this weekend, backed up by quite a bit of evidence.

The primary instability right now is deep slab on top of persistent weak layers. We havent been able to do a crown profile since the most recent storm, but all the characteristics incriminate the old facets and buried surface hoar, which formed during our two extended high-pressure events in December and January. Snowpit tests could easily show false stable results and inspire unjustified confidence in the snowpack. The distribution of the weak layers and the depth of the slab on top is too variable to make confident and accurate evaluations.


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Encyclopedia of avalanche terms.

ANNOUNCEMENTS
The Friends of the CNFAIC (FCNFAIC) needs your thoughts! With a new staff of forecasters and a list of previously completed goals, the program is growing and potentially heading in new directions. The FCNFAIC wants to know what you have to say about YOUR avalanche center, so please complete the following anonymous survey by February 20th. Thank you in advance for taking it!
Click here to take survey

or cut and paste the address directly:
https://www.surveymonkey.com/s/THWXVCD

WEATHER ROUNDUP
The recent storm finished 48 hours ago. Total storm accumulation ranged from only 10-15 inches snow in upper elevations in Summit to over 50 at upper elevations in Girdwood. Turnagain pass was middle range with about 29 inches up high. Rain to 2000 feet saturated the lower elevations and is evident with a crust below treeline. Wind during the storm trended from the East with gusts into the 60s at the ridge-tops. Wind distribution from the storm is evident through the region. Temperatures have dropped since the storm started diminishing and remain below freezing but moderate. A few inches of colder snow fell at the tail end of the storm. Today clear skies, moderate temperatures, and light wind are expected. A chance of snow showers starts tonight but little precip is expected at this time.

Wendy 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:
WESTERN PRINCE WILLIAM SOUND-
INCLUDING...WHITTIER...SEWARD...GIRDWOOD...MOOSE PASS
500 AM AKST SAT FEB 5 2011

.TODAY...MOSTLY SUNNY. HIGHS IN THE LOWER 20S TO LOWER 30S...
WARMEST ALONG THE COAST. NORTH TO EAST WIND TO 15 MPH.
.TONIGHT...PARTLY CLOUDY. A CHANCE OF SNOW SHOWERS ALONG THE
GULF COAST. LOWS 10 TO 20 ABOVE INLAND AND LOWER TO MID 20S
ALONG THE COAST. LIGHT WINDS EXCEPT NORTH WIND 10 TO 20 MPH
NEAR SEWARD.
.SUNDAY...MOSTLY CLOUDY. A CHANCE OF SNOW SHOWERS IN THE MORNING
ALONG THE GULF COAST. HIGHS IN THE LOWER 20S TO LOWER 30S...
WARMEST ALONG THE COAST. LIGHT WINDS EXCEPT NORTH WIND
10 TO 15 MPH NEAR SEWARD.
.SUNDAY NIGHT...MOSTLY CLOUDY. LOWS 5 TO 15 ABOVE INLAND AND
MID 20S ALONG THE COAST. LIGHT WINDS.
.MONDAY...MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS. HIGHS
IN THE LOWER 20S TO LOWER 30S...WARMEST ALONG THE COAST.
LIGHT WINDS.
.MONDAY NIGHT...MOSTLY CLOUDY WITH A CHANCE OF SNOW. LOWS IN
THE 20S.
.TUESDAY THROUGH WEDNESDAY...SNOW AND RAIN LIKELY. HIGHS IN
THE 30S. LOWS IN THE 20S.
.WEDNESDAY NIGHT...SNOW LIKELY. LOWS IN THE 20S.
.THURSDAY AND THURSDAY NIGHT...MOSTLY CLOUDY WITH A CHANCE OF
SNOW SHOWERS. HIGHS 25 TO 35. LOWS IN THE TEENS.
.FRIDAY...MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS. HIGHS IN
THE 20S.


TEMPERATURE / PRECIPITATION

SEWARD 31 22 32 / 0 30 30
GIRDWOOD 25 16 25 / 0 0 0




WEATHER STATION SUMMARY for Turnagain Pass:
-3800 Sunburst Wx Station-
Temperature 20, on a rising trend. Wind is picking up slightly, steady at 11-15mph currently.
-2600 Seattle Ridge Wx Station-
Temperature 17 degrees. Recent wind gust to 27 in the last hour.
-1800 Center Ridge Wx Station-
Temperature 18 degrees. One inch of snow settlement in the last 24 hours.

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: Apr 28, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: ClosedSKOOKUM DRAINAGE CLOSED TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: OpenOpen thru May 14th.
Twentymile: Closed
Seward District
Carter Lake: OpenClosed May 1.
Lost Lake Trail: OpenClosed May 1.
Primrose Trail: OpenClosed May 1.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: OpenClosed May 1.
South Fork Snow River Corridor: OpenClosed May 1.
Summit Lake: OpenClosed May 1.

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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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