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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, December 19th, 2011 - 7:00AM
Expires
Tue, December 20th, 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 Monday, December 19th 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).

ANNOUNCEMNTS

There will no advisory issued tomorrow, Tuesday. The next advisory will be issued Wednesday, December 21st, at 7am. See Tuesday’s outlook below.

BOTTOM LINE

There is a CONSIDERABLE avalanche danger today for unmanageable soft slab and wind slab avalanches formed in yesterday’s 2+ feet of new snow. This means human triggered avalanches are likely and will be deep and dangerous if released. Most probable areas to avalanche are steep slopes near and above treeline. The snowpack is currently adjusting to yesterday’s rapid load and needs time to bond.

AVALANCHE DISCUSSION

AnCNFAIC Staff rapidly intensifying storm rolled through our region yesterday. In a roughly 12 hour span, 2 feet of snow fell in the Turnagain Pass area, with a bit more in the Girdwood Valley and less in the Summit Lake area. Gale force easterly winds accompanied the snow and an ensuing natural avalanche cycle was seen/reported in the Girdwood area. The poor visibility kept observations limited as to the extent of CNFAIC Staff natural activity.

Human triggered soft slab and wind slab avalanches will be the primary concerns. These are likely to be unmanageable with the amount of new snow that fell yesterday. Avoiding steep slopes today is advised as it has only been 24hours since the storm and we do not know exactly how the pack is reacting. The decreasing temperatures today will help to lock things in place, but do not count on it yet. Wind deposited areas are likely to be deep and soft and cornices large and sensitive. Cornices will deserve a wide berth. Expert level route-finding skills and terrain management will be required in the backcountry today.

Tuesday’s Outlook

Tuesday, the avalanche concerns will be similar to Monday with a decreasing trend in danger as the snowpack heals. However, any new snow and wind Monday night will increase the danger for new snow instabilities.

MOUNTAIN WEATHER

Yesterday’s quick and dirty storm laid down anCNFAIC Staff good shot snow in most locations. Turnagain Pass saw 2′, mid-elevations in the Girdwood Valley 2 ½’ with Summit Lake around 1′ at 1400′. The last two weekend storms have doubled the Turnagain Pass overall snow depth. Easterly winds again tore through the region with 50-60mph hourly averages and over 100mph gusts. The sunburst wind sensor finally died after reporting a 104mph gust. The storm decreased significantly in the afternoon and overnight winds and have been moderate from the south, with stronger southerly gusts in the Summit area. Temperatures have decreased as well and are currently around 30F at sea level, mid 20’s around treeline and 20F on the ridges.

Today, partly to mostly cloudy skies will fill back in with a pulse of weather moving through later in the day. Light to moderate SW winds will turn SE with a chance for a couple of inches of snow tonight.

Tuesday, the weather looks to pick up in the afternoon with increased wind, and possibly snow, ahead of anCNFAIC Staff system moving in on Wednesday.

CNFAIC Weather Page and the NWS forecast

Kevin will issue the next advisory Wednesday 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.

Mon, December 19th, 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.