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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, December 5th, 2011 - 7:00AM
Expires
Tue, December 6th, 2011 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Good morning. This is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Monday, December 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).

ANNOUNCEMNTS

There will be no advisory issued tomorrow, Tuesday, Dec. 6th. The next advisory will be on Wednesday, Dec. 7th at 7am. Look for “Tuesday’s outlook” below.

BOTTOM LINE

The avalanche danger is CONSIDERABLE on all mid to upper elevation slopes for wind slab and soft slab avalanches. Strong winds, rain and snow over the weekend rapidly loaded slopes and initiated a natural avalanche cycle. The pack has not had enough time to adjust to the new load and human triggered avalanches are likely today. There is also a MODERATE danger at low elevations for wet avalanches in areas where the wet snow has not frozen and remains loose.

AVALANCHE DISCUSSION

Anyone driving between Anchorage and Portage may want to check out the debris piles on the side of the highway. These are from yesterday’s naturally and artificially triggered avalanche activity. In addition, there was widespread natural activity seen from Girdwood to the southern Kenai. These avalanches were in the form of wind slabs, wet slabs and wet loose slides. A very warm and intense storm dropped between 1 and 2.5″ of rain at low elevations and between 1 and 2 feet of snow at high elevations. These amounts are not huge, by any means, but the rain and warm snow fell quickly and on a relatively ‘cold’ snowpack, shocking the system, and initiating an avalanche cycle at all elevations.

The Turnagain Pass area was shrouded in clouds yesterday, but by late afternoon clouds lifted just enough to see only a few natural avalanches. Hence, many of these slopes could be plastered in place or, more likely, ‘hanging in the balance’. Only 24 hours has passed since the natural cycle and, experience tells us, this is the time most human triggered avalanches occur.

Today, wind slab and soft slab avalanches are the primary concerns. The bonding of the new snow and recent wind deposited snow to the old surface should be treated as untested and, until proven CNFAIC Staffwise, unstable. Watch for cracking in the new snow and hollow, stiff feeling wind pillows and pockets. The steepest part of a rollover, off ridge lines and above gullies are areas most likely to trigger a slide.

Any low elevation slopes that have not refrozen from the rain on snow event, or have only refrozen on the surface, are suspect to slide with the weight of a sled and/or person. Wallowing in wet saturated snow will be the best clue that the snow has not set up yet.

Some of the natural activity from yesterday looks like it may have ‘stepped’ down and broke into the old weak faceted snow mid-pack. We will be investigating this as skies clear, but it is something to keep in mind. If these faceted layers are reactive, avalanches will be larger and deeper than just the storm snow.

Tuesday’s Outlook

Tuesday the avalanche concerns will be similar to today. It will have been roughly 48 hours after the end of the storm and the snowpack should have had time to adjust. Watch for lingering wind slabs in the upper elevations, on rollovers and cross loaded gullies.

MOUNTAIN WEATHER

The weekend storm has dissipated and left us with a total of over 2″ of water equivalent in the Girdwood Valley, ~1.5″ at Turnagain Pass, ~1″ at Summit Lake and over 2″ south of Summit Lake. Locations below 2000′ saw mostly rain, however, upper elevation snowfall can be estimated by multiplying these water numbers by 10. Skies have cleared overnight and temperatures have dropped to near 32F at sea level and to the mid-teens at 3000′. Winds have been gusting in the 30’s from the west. Today temperatures should be in the 20’s at most locations above 1000′ and winds moderate, gusting from the NW in the 30’s on the ridgelines. Skies look to be partly cloudy.

Tuesday, a lull in the weather continues ahead of what looks to be anCNFAIC Staff shot for snow Wednesday. Expect temperatures to remain in the mid-teens to 20’s and partly to mostly cloudy skies. Winds look to be light to moderate.

CNFAIC Weather Page and the NWS forecast

I will issue the next advisory Wednesday morning at 7am. 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.

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Mon, December 5th, 2011
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

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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.