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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 22nd, 2017 - 7:00AM
Expires
Sat, December 23rd, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A CONSIDERABLE  avalanche danger exists in the Alpine. Natural wind slab avalanches 1-2′ thick are possible today due to strong winds over the region. Wind loading on the high elevations slopes (above 3,000′) may also overload the snowpack and cause a deep slab avalanche to release that breaks near the ground.  Careful snowpack evaluation and conservative decision-making is essential.

The avalanche danger below 2500′ is MODERATE  for wind slab avalanches around a foot thick. At these lower elevations, watch for wind loaded slopes where triggering a shallow wind slab is possible.  There is no hazard below 1,000′ due to lack of snow.

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Fri, December 22nd, 2017
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

Skies may be mostly clear, but the winds are howling along the ridgelines. Beginning yesterday, sustained Easterly winds in the 20-40mph range are impacting the mountains. There were no known avalanches yesterday. However, there was a report of a crown and large avalanche in the Center Divide area near Johnson Pass. It is unknown when this avalanche released and we hope to get better eyes on it today. It does appear to have been a large slab breaking near the ground. 

For today, wind slabs will be the primary concern. Watch for these not only in the upper elevations, but in the lower elevations as well. Terrain channeling may be occurring which can load slopes below treeline. In the Alpine, the main concern will be both wind slabs and deep persistent slabs (more on the deep slabs below). Today is a day to watch for wind loading patterns and feeling for stiffer snow over softer snow. Watch for cracks that shoot from your feet. All these signs point to touchy wind slabs. We could see some cornice falls and wind slabs release naturally; if this is the case, these may be able to trigger a deeper avalanche at the upper elevations. 

Strong Easterly winds blowing snow on Seattle Ridge yesterday afternoon.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

As mentioned above, at elevations above 3,000′ weak snow sits below a very hard and dense slab. Many of you have likely heard about the large avalanche that was remotely triggered by 2 skiers on the lower benchs of Pastoral Peak on Wednesday. This is unfortunately prime eveidence that the deep persistent slab problem is out there and looming on other upper elevation slopes. We were able to do an avalanche investigation yesterday, see that HERE. This is a low probability, high consequence avalanche issue. It is a tough situation as this problem does not tend to go away quickly. Additionally, these types of avalanches are hard to trigger, thus can lull us into a sense of complacency when days pass with no incidents. Here are some points to consider as we move forward:

–    This danger is on the upper elevations slopes, above 3,000′.

–    No RED FLAGS may be present before an avalanche releases.

–    Several tracks may be on a slope before someone finds the trigger point and releases the slope.

–    The ‘slab’ above the weak snow sitting on the ground is 3,4,5+ feet thick, this means it is difficult to trigger.

–    Because there is variability in the slab thickness, there are places the slab is only 1-2′ thick, or less. These areas are where a person/group of people’s weight can penetrate to the weak layer and trigger a collapse that can then trigger a large avalanche (this is what happend on Pastoral Wednesday).

As this problem persists, steering clear of slopes over 30 degress at the upper elevations, along with runout zones, will be a safer way to enjoy the backcountry.

Photo below of the Pastoral avalanche on Wed, Dec 20th (photo taken on Dec 21st). The route of the skiers is marked on the photo. This is a good reminder that our snowpack ‘set up’ above 3,000′ requires another look at our ‘safe spots’. These large avalanches can send debris where we have not seen debris for 10 years. 

Photo looking down toward Taylor Pass from Pastoral debris.

 

A look into the snowpack near the point the Pastoral avalanche was triggered.

 

 

 

Weather
Fri, December 22nd, 2017

Partly cloudy and windy skies filled the region yesterday. Ridgetop winds have been the primary weather driver as no precipitation has fallen since Tuesday and temperatures are holding steady in the 20’sF at most elevations and near 30F at sea level. Over the past 24-hours winds have been generally Easterly along ridgelines averaging 20-30mph with gusts to 50mph. Since midnight, temperatures have risen a few degrees as slightly warmer air is streaming in.  

Today, and tomorrow, we are expecting mostly sunny skies and WINDY conditions. Easterly ridgetop winds are slated to increase through the day with averages in the 30-50’s mph and stronger gusts. No precipitation is expected as the Eastern Turnagain Arm region and Kenai sit on the dry side of a large frontal boundary. Temperatures look to climb slightly with warmer air moving in, up to the mid 20’s at 3,500′ and 30F at 1,000′.  

For Christmas Eve and Day, it looks like Santa could be gifting us a round of snowfall. Stay tuned for more on this tomorrow!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   0   0   31  
Summit Lake (1400′) 16   0   0   12  
Alyeska Mid (1700′) 26   0   0   27  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22*   NE*  27* 53*  
Seattle Ridge (2400′) 24   SE   23   47  

*Sunburst weather station in back ONLINE!! Thanks to Alpine Air for the battery transport and Friends- CNFAIC board members (past and present) Crane Johnson and Jeff Conway for the labor!

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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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