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Issued
Sun, December 18th, 2011 - 7:00AM
Expires
Mon, December 19th, 2011 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Good morning. This is Wendy Wangner with the Chugach National Forest Avalanche Information Center on Sunday, 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).

BOTTOM LINE

The avalanche danger is CONSIDERABLE for storm snow and wind slab avalanches on all slopes steep enough to slide. Strong winds and heavy snowfall is expected today. This means natural avalanches are possible and human triggered avalanches are likely on slopes steeper than 30 degrees. There are pockets of HIGH danger for any area receiving more than 18″ of new snow with high winds over the course of the day.

AVALANCHE DISCUSSION

Yesterday, soft wind drifts, slabs and cornices were beginning to develop as easterly winds picked up ahead to today’s storm. These wind deposited areas were just becoming sensitive in the afternoon and have only increased in size and sensitivity with the overnight winds and new snow.

Rapidly changing weather will dictate the avalanche conditions today. Developing strong to hurricane force winds will increase along with heavy snowfall this morning and into early afternoon. High precipitation rates, 2-3″ per hour, are likely, especially during the late morning. Around 10-12″ of new snow has already fallen in the Girdwood Valley with 8″ at Turnagain Pass at the mid-elevations. This storm is similar to last Sunday’s event, however, less overall snowfall is forecast.

Today’s primary concerns are storm snow and wind slab avalanches. These are possible to release naturally and likely to be triggered by a human. If the weather forecast intensifies, natural avalanches will be likely and human triggered avalanches very likely. Travel in, and under, avalanche terrain is not advised today. Expert level terrain management skills are necessary for anyone deciding to brave the gale force winds and driving conditions to head into the backcountry.

MOUNTAIN WEATHER

Today, yet anCNFAIC Staff strong Sunday storm is bearing down on us, or as the NWS put it in yesterday’s discussion: “STAY TUNED FOR ANCNFAIC Staff SUNDAY FULL OF WILD WEATHER”. Overnight, around 8″ of snow has fallen in the Turnagain Pass area and around 10-12″ in the mid-elevations of the Girdwood Valley.

The strong easterly winds that have developed early this morning are forecast to increase to near 80mph through Turnagain Arm and on the ridge tops. In fact, the Sunburst weather station just reported a 98mph gust. The Weather Service has issued a HIGH wind warning for the Eastern Turnagain Arm. Snowfall is expected to be heavy at times, dropping anCNFAIC Staff 10-18″ today, and possibly more, in favored locations. Girdwood Valley looks to be the most favored area for high precipitation rates at this point. The rain/snow line looks to be hovering around 500′. Temperatures will remain mild, in the mid 30’s F at sea level to the mid 20’s at 3000′ with overcast and obscured skies. The storm is expected to move out later this afternoon.

CNFAIC Weather Page and the NWS forecast

I will issue the next advisory tomorrow morning. If you get out in the backcountry we want to know what you are seeing. Please send us your observations using the button at the top of this page or give us a call at 754-2369. Thanks and have a great day.

Sun, December 18th, 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. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. 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.