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Issued
Tue, February 8th, 2011 - 7:00AM
Expires
Wed, February 9th, 2011 - 7:00AM
Forecaster
Jon Gellings
Avalanche risk The Bottom Line

Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, February 8th 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 danger is increasing to CONSIDERABLE for today. If the forecast becomes verified, then several inches of new snow and strong easterly winds will have created dangerous avalanche conditions. Shallow areas of the snowpack are suspect for deep slab avalanches. Areas of sensitive wind slabs created last night and today could break and step down to our previously buried weak layers. Triggering these deep slab avalanches from thin spots in rocky terrain, or areas with a shallow snowpack, is likely.

AVALANCHE DISCUSSION

There was one reported snowboarder triggered avalanche in our advisory area yesterday. This was on a south facing slope around 3400′ on Magnum, and is estimated at 150-200′ wide, 600-800′ long, and 2-3′ deep in most areas; up to 5′ deep in some areas.

Over the past two days, we have heard/felt large collapses (which created “whoomph” sounds), heard of two new human triggered avalanches, and saw one new natural avalanche (Glide Avalanche photo in gallery). This information, coupled with increasing stress on an already sensitive snowpack, warrants increasing caution while travelling on or around slopes steeper than 30 degrees. The weak layers of greatest concern are the faceted snow grains from cold, High Pressure weather events during December, and buried up to several feet deep on top of the Thanksgiving Rain Crust (TRC).

Our previous weather events have left us with a classic slab avalanche recipe in many areas. Our 2010-11 mixing bowl consists of a growing 2-4+’ hard slab, layered above 6” – 2′ of weak faceted snow. If you load all of this on top of a good sliding surface (TRC) in suitable terrain, the potential avalanche is ready to go. This image shows an example of the situation we are dealing with:

Our snow cover this year is showing below average depth, and is comprised of a variety of weak layers. This setup has shown us two different areas to trigger our current deep slab so far. One is in the upper elevation rocky terrain, where variably thin spots exist and a person could collapse a buried weak layer and trigger an avalanche. The CNFAIC Staff is in regions where the overall snow depths are shallow. Remotely triggering an avalanche from above, from the side, or from below, is LIKELY and more widespread (Johnson Pass and south through Summit Lake and north through the Girdwood Valley area). Avalanches in these areas could potentially break large with high consequences, so avoiding terrain closely connected to slopes above 30 degrees is recommended. 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 weather is changing from clear yesterday, to stormy today. Easterly winds are increasing, and temperatures are forecasted to increase as well. There is a large amount of precipitation being aimed toward us from Prince William Sound, but it is currently being absorbed by the glacial buffer.

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 TUE FEB 8 2011

…STRONG WIND THROUGH LATE THIS EVENING THROUGH PORTAGE VALLEY

AND TURNAGAIN ARM…

.TODAY…SNOW…BECOMING MIXED WITH RAIN ALONG THE COAST. SNOW

ACCUMULATION 4 TO 8 INCHES. HIGHS IN THE 30S. NORTH TO EAST WIND

10 TO 25 MPH WITH GUSTS TO 35 MPH NEAR WHITTIER IN THE AFTERNOON.

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 30 TO 45 MPH

INCREASING TO 45 TO 60 MPH IN THE AFTERNOON.

.TONIGHT…RAIN AND SNOW BECOMING ALL RAIN NEAR SEA LEVEL.

ADDITIONAL SNOW ACCUMULATION 2 TO 4 INCHES THROUGH TURNAGAIN

PASS. LOWS IN THE LOWER TO MID 30S. NORTH TO EAST 10 TO 25 MPH

WITH GUSTS TO 35 MPH NEAR WHITTIER…DECREASING TO 15 MPH OR LESS

AFTER MIDNIGHT. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST

WIND 40 TO 55 MPH DECREASING TO 25 TO 40 MPH AFTER MIDNIGHT.

.WEDNESDAY…RAIN. HIGHS IN THE MID 30S TO LOWER 40S. SOUTH

TO EAST WIND 5 TO 20 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 38 34 39 / 100 100 80

GIRDWOOD 35 34 38 / 100 90 80

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station- Temperature 17F degrees. Winds are blowing strongly from the ENE, gusting to 47mph currently.

-2600′ Seattle Ridge Wx Station- Temperature 21F degrees. Winds are blowing strongly from the SE, gusting to 55mph currently.

-1800′ Center Ridge Wx Station- Temperature 28F degrees. No new snow. Current snow depth 83 inches.

Tue, February 8th, 2011
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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.