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Issued
Fri, February 18th, 2011 - 7:00AM
Expires
Sat, February 19th, 2011 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Friday, February 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).

BOTTOM LINE

The avalanche hazard rating is still MODERATE but a little higher than yesterday. 2-4 inches of new snow fell overnight with a little more expected today. Old and new wind slab will be a concern in specific areas near ridges in wind deposition zones. The deep persistent instabilities are less likely to be found but probably more dangerous.

AVALANCHE DISCUSSION

New snow overnight is the news of the day. It looks like only a small amount of accumulation and relatively light wind will keep the rising hazard to a minimum. Any new snow will create changes, so be aware that conditions are not what they were yesterday. New wind slabs overnight are likely.

There was a report yesterday of a significant natural avalanche in the Grandview region. This is a surprising event, being nearly 1 week after the last significant snowfall. Wind was the big factor to create a heavy enough slab and to trigger its release. It’s a good reminder that despite our best prediction efforts we do see events that seem unlikely. Wind transport of the last cold dry snow has been widespread, creating slabs that can be triggered by skiers or snowmachines.

Our deep slab problem is still out there even though we don’t have many recent reports. An avalanche on Monday on Raggedtop is a good example of the complicated problems right now. This skier triggered avalanche involved both recent windslab and stepped into deeper older weak layers. See a photo and analysis here.

The common theme for the deeper instabilities is a shallow snowpack. Regions on the Kenai or the Chugach with thinner average snow depths are more likely to have avalanche problems. Some areas include Summit, Johnson Pass and the interior Kenai. Also the Crow Pass area of the Girdwood Valley has proven to be shallow. In deeper areas the shallow points can be trigger spots, which can then release a deeper slab connected to it.

WEATHER ROUNDUP

Eastern Turnagain arm got 2-4 inches of low density snow overnight. An additional 2-4 is predicted today. Wind was relatively light with some gusts into the 30s at ridgetop stations coming from variable directions. Wind channeled through Turnagain arm was a little stronger with some gusts into the 50s. The Front moving across our region today is expected to pass with precip dying out today. Through the weekend mostly clear to partly cloudy skies are predicted with moderate temperatures.

ANNOUNCEMENTS

The Forest Service is installing winter use bridges across Granite creek in Turnagain Pass. Be aware of an ice road from the Lyon creek bridge south towards Johnson Pass on the West side of the highway. Heavy equipment will also be used in the area.

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

I 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 FRI FEB 18 2011

…STRONG WIND SATURDAY MORNING THROUGH SATURDAY EVENING NEAR

WHITTIER…

.TODAY…SNOW IN THE MORNING WITH AREAS OF BLOWING SNOW ALONG

TURNAGAIN ARM. SCATTERED SNOW SHOWERS IN THE AFTERNOON. SNOW

ACCUMULATION UP TO 2 INCHES. HIGHS IN THE MID 20S TO MID 30S.

VARIABLE WIND 10 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM…SOUTHEAST WIND 20 TO 35 MPH BECOMING VARIABLE 10 MPH

IN THE AFTERNOON.

.TONIGHT…MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS. LOWS 15 TO

25. NORTHWEST WIND 10 TO 15 MPH EXCEPT WEST 20 TO 35 MPH NEAR

WHITTIER.

.SATURDAY…MOSTLY SUNNY. HIGHS IN THE LOWER 20S TO LOWER 30S.

NORTHWEST WIND 10 TO 15 MPH EXCEPT WEST 30 TO 50 MPH NEAR

WHITTIER.

.SATURDAY NIGHT…MOSTLY CLEAR. LOWS 10 TO 20 ABOVE. NORTHWEST

WIND 10 TO 20 MPH. NEAR SEWARD…NORTH WIND 15 TO 30 MPH

DECREASING TO 10 TO 20 MPH AFTER MIDNIGHT. NEAR WHITTIER…WEST 30

TO 50 MPH DIMINISHING TO 15 TO 25 MPH AFTER MIDNIGHT.

.SUNDAY…PARTLY CLOUDY. HIGHS IN THE LOWER 20S TO LOWER 30S.

VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTH WIND 15 MPH.

.SUNDAY NIGHT…PARTLY CLOUDY. LOWS IN THE TEENS.

.WASHINGTONS BIRTHDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW.

HIGHS IN THE 20S.

TEMPERATURE / PRECIPITATION

SEWARD 34 24 30 / 80 0 0

GIRDWOOD 28 15 29 / 80 20 0

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

Temperature 14, on a decreasing trend. Wind shifted overnight from West to SE. Recent gusts to 20.

-2600′ Seattle Ridge Wx Station-

Temperature 16. Wind is steady in the 20s gusting to 29 from the ESE

-1800′ Center Ridge Wx Station-

Temperature 20 degrees. 2-3 inches of light snow fell overnight.

Fri, February 18th, 2011
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Dangerous avalanche conditions. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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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.