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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, December 4th, 2017 - 7:00AM
Expires
Tue, December 5th, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

Continued snowfall, rain and wind will keep the avalanche danger at HIGH again today. A warm, wet and windy storm has overloaded the snowpack in the Girdwood, Portage, Turnagain Pass and Kenai Mtn regions. Natural avalanches are expected again today and human triggered avalanches are very likely. Travel in avalanche terrain is NOT recommended.  

Below 1,000′ there is a CONSIDERABLE danger where predominantly rain is falling. Debris running into these lower elevations from avalanches above is likely along with wet loose avalanches on steep slopes.  

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Mon, December 4th, 2017
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
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

As of this morning, the potent storm over us is slowly degrading and exiting. The good news is, winds (that were off the chart yesterday) have decreased overnight and snow is still falling. The rain/snow line is just above 1,000′ currently and forecast to lower to around 800′ with slightly cooling temperatures. We should see an additional 4-8″ through the day at the higher elevations with another 3-4″ tonight. Curious of the snow totals so far? 

Estimated Storm Totals (beginning 6am yesterday till 6am today):

Girdwood Valley:  ~2″ rain lower elevations, 2-3+’ snow high elevations
Turnagain Pass:  1.8″ rain lower elevations, 2-3+’ snow high elevations
Summit Lake:   .3″ rain lower elevations, 3-8″ snow high elevations

Recent avalanche activity? There is much uncertainty as to the extent of the natural avalanche cycle yesterday and overnight. As is the case during these stormy conditions, low visibility and darkness hamper visual observations. Nonetheless, we can expect that the mountains are still undergoing significant changes. Upper elevations have seen 2-3+’ of feet of snow in less than 24 hours – and it’s still snowing and blowing… This is a simple rapid loading event and a text book case for how-to-make-avalanches. Hence, steering clear of avalanche terrain (slopes over 30 deg) with nothing above you (avoiding runout zones) is essential.

 

If we dig a bit deeper into what the mountains are going through and a look to the future, many slopes could be sliding, or will soon, and fill back in. This is what we’d like to see because it helps to clean out the weak layers from November. However, there are those slopes that will hang in the balance and allow the snow to pile up. These are the most likely ones that can get us in trouble when the storm passes. They will still have the weak snow under the new snow, which makes them more susceptible to human triggers, and they will also produce larger avalanches. Telling the difference from slopes that have slid and ones that haven’t can be difficult to impossible. Also, just because a slope slid doesn’t mean it won’t again, especially the first couple days after this cycle. Keep these thoughts in the back of your head as you look forward to enjoying the new snow.  

Weather
Mon, December 4th, 2017

Yesterday’s warm storm began around 9 am and as of 6am this morning ~1.5 – 2″ of rain has fallen below 1,000′ and 2-3+’ of snow above. The rain/snow line crept up last night and is hovering just above 1,000′. Winds were some of the strongest we have seen for a while from the East, averaging 40-70mph with gusts over 100. Winds have backed off to the 20-30mph range for averages this morning, remaining from the East. Temperatures have been near 38F at sea level and the upper 20’s on the higher ridgelines.

Today, we should see the rain/snow line lower to 800′, possibly further, with .4-.5″ of rain below and 4-8″ of snow above. Tonight cooler air should continue to drop the rain/snow line and an additional 3-4″ is possible at sea level with 4-6″ at the higher elevations. Winds are forecast to shift Southerly and decrease somewhat to 15-30mph. Temperatures are expected to hover near 38F at sea level and the upper 20’s on the 3,500′ ridgelines.

Tuesday, the slightly cooler air is expected to stay in place as this system continues its slow exit. We could see continued snowfall with a rain/snow mix at sea level. Looking toward to later this week, warmer air and precipitation looks to filter back our way. Stay tuned.

*Center Ridge SNOTEL is reporting erroneous temperature data. See  Turnagain Pass DOT weather station  for accurate temperature at 1000′.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) *31   15   1.8   31  
Summit Lake (1400′) 34   0   0.3   9  
Alyeska Mid (1700′) 33   2   1.7   20  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24   ENE   59   124!!  
Seattle Ridge (2400′) 28   SE   25   61  
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Riding Areas
Updated Wed, December 11th, 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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