Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 25th, 2015 - 7:00AM
Expires
Sat, December 26th, 2015 - 7:00AM
Forecaster
CNFAIC Staff
The Bottom Line

The avalanche danger will increase to CONSIDERABLE today as a strong winter storm impacts the advisory area. Periods of heavy snow combined with wind are forecasted. The new snow will land on a weak snow surface in most of the terrain. The hazard could increase quickly. Human triggered avalanches will be likely and natural avalanches will be possible. Caution is advised as conditions change. The danger may go to HIGH by the evening.

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Fri, December 25th, 2015
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)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

A winter storm warning is in effect for the region today. If the forecasted snow totals verify we could quickly start to have storm snow concerns. Initially we could see loose snow avalanches. The new snow will land on weak snow. Surface hoar and near surface facets have formed during the past few days on all aspects and elevations. These could become a very reactive weak layer as the new snow piles up. Winds have destroyed the surface hoar in some areas in the Alpine but unfortunately we will not have x-ray vision to determine exact distribution. The winds have already started to pick up this morning. This combined with the new snow could rapidly create sensitive slabs. Pay close attention to changing conditions. Watch for heavy precipitation intensity, strong winds, shooting cracks and whumpfing. Low visibility will make it hard to see what is above you. Avoid travel in runout zones. If you do venture out today conservative terrain choices are advised. 

Yesterday’s snow surface = Today’s weak layer. 

 

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

The weak snow that formed in early December sitting over the Thanksgiving Rain Crust or old hard snow is now buried under 2-4′ of snow. This combination has been the cause for concern and heightened caution in the backcountry for the past week. This setup could now become overloaded with the additional weight of new snow and wind loading. If avalanches step down into this layer, they could be quite large and destructive. 

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

There have been cornice triggered avalanches during the past week and there are looming sections overhanging slopes today. Cornices will grow quickly with the new snow and may be triggered by the increasing winds. Visibility may make it challenging to see what is above. This is an added reason to stay away from runout zones.

Weather
Fri, December 25th, 2015

Yesterday was clear in the morning with increasing clouds throughout the day. Winds were light and shifted from W to E. Temperatures were in the single digits in the valleys and the mid-teens at ridge tops.

The winds have picked up this morning and temperatures are warming as the weather system approaches.

NWS Zone Forecast for Turnagain:

…WINTER STORM WARNING FOR HEAVY SNOW REMAINS IN EFFECT FROM
9 AM THIS MORNING TO 6 AM AKST SATURDAY…

* SNOW…13 TO 26 INCHES…HIGHEST AMOUNTS THROUGH TURNAGAIN PASS AND
NEAR GIRDWOOD.

* VISIBILITY…NEAR ZERO AT TIMES IN HEAVY SNOW AND BLOWING SNOW.

* WIND…EAST WIND 10 TO 25 MPH EXCEPT EAST 40 TO 55 MPH THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM…STRONGEST WINDS THIS
EVENING.

* TIMING…SNOW WILL DEVELOP THIS MORNING THEN BECOME HEAVY THIS
AFTERNOON. HEAVY SNOW WILL CONTINUE THROUGH TONIGHT FOR INLAND
AREAS BEFORE DIMINISHING EARLY SATURDAY MORNING. LOCATIONS ALONG
THE COAST WILL CHANGE TO RAIN LATE THIS AFTERNOON OR EVENING
RESULTING IN LESS SNOW ACCUMULATION OVERALL. The rain/snow line is expected to rise to 500′ tonight.

The storm continues into tomorrow with snow/rain showers and easterly winds. Temperatures will be in the high 20Fs to mid 30Fs.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 15    0 0   49  
Summit Lake (1400′) 10    0 0  17
Alyeska Mid (1700′) 15  0   0 35  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14   ESE   8   15  
Seattle Ridge (2400′) 14 ESE  10 14  
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Riding Areas
Updated Mon, December 02nd, 2019

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

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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