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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, April 6th, 2017 - 7:00AM
Expires
Fri, April 7th, 2017 - 7:00AM
Forecaster
Graham Predeger
The Bottom Line

HIGH avalanche danger persists today as another wave of wet, warm and windy weather impacts the advisory area.   Natural avalanches are likely and human-triggered avalanches are very likely.   TRAVEL IN AVALANCHE TERRAIN IS NOT RECOMMENDED. If choosing to play in the flats (and rain) today, steer well clear of gullies and the bottom of steep slopes as many avalanches have been running full track to valley floors.  

Hiking in Portage Valley:    Avalanches occurring at the higher elevations can send large amounts of debris into valley bottoms and cover snow-free hiking trails. Avoid trails that cross under avalanche paths such as Byron Glacier or portions of the Trail of Blue Ice.

Summit Lake:    Several natural avalanches observed yesterday.   Travel in avalanche terrain is not recommended.  Read the  Saturday Summit Summary  HERE.

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Thu, April 6th, 2017
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
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
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

For the past week, observations have been limited due to elevated avalanche danger and poor visibility.  A brief window into the alpine yesterday confirmed our suspicions that we are still within a very active natural wet avalanche cycle.  Temperatures were the warmest we’ve seen all spring at ridge top locations yesterday and the mountains surrounding Turnagain Pass appear to be going thru a spring ‘shed-cycle’ of sorts.  Large natural avalanches are failing on all aspects, particularly in the mid-elevation band below about 2,500’ and showing potential to propagate across wide distances.  What hasn’t avalanched yet will be stressed by another half inch of water weight today.  These could fail either as storm slabs (2-4’ deep) or step down into weaker snow near the ground (4-6+’ deep).  At this point it doesn’t really matter what the weak layer because this is not an avalanche problem to mess with or try and out-smart.  The snowpack will remain touchy and with natural avalanches likely again today, travel in avalanche terrain is not recommended.  Avoidance will be your best and only tactic until this warm and wet pattern of storms subsides and we can take stock of what is left of our snowpack.  

 Nearly wall to wall avalanching on Seattle ridge (lookers left of the common snowmachine up-track) “Repeat offender” path as viewed from the Seward Highway.

WIND SLABS and CORNICES:

Strong winds last night combined with more snow will act to create large wind slabs and cornices on leeward slopes in the upper elevations.  With temperatures rising to above freezing in the alpine these may release naturally and could entrain enough snow to run quite far. Any additional wind and precipitation today will add further stress.

How much load is on the old weak surface from March? Storm totals (March 27 – 6am April 6th):

Turnagain Pass:     4.7″ of H2O, 48+” of snow at upper elevations
Girdwood Valley:    5.5″ of H2O,  55+” of snow at upper elevations
Summit Lake:         1.6″ of H2O,  15+” of snow at upper elevations   

Widespread avalanching on Eddie’s lower rolls as seen from the RWIS web cam during a brief period of clearing yesterday afternoon.

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 balance has been tipped and avalanches this week have been observed stepping down into old weak layers. Dirty debris in places is indicative that some avalanches were running to the ground. Prior to this storm cycle the snowpack consisted of many weak layers of facets and buried surface hoar. We may continue to see avalanches today breaking in the mid-pack or near the ground, with crown depths over 6′ and running the entire length of a slide path.  Again, avoidance is key with this problem as a persistent slab avalanche in our current snowpack is not a survivable event.

Recent full-depth avalanche on Seattle ridge (across from Sunburst) stripping out the entirety of our snowpack. 

Weather
Thu, April 6th, 2017

Daylight hours yesterday provided a brief reprieve from the deluge of wet, cloudy weather (enough to view the alpine) though we still ended the 24-hour period with .5 – .7 € of water and likely another 5 €“ 10 € of snow above the freezing line (~2,000′).   Temperatures were WARM with the Center ridge SNOTEL topping out at 44 degrees (1,880′) and Sunburst weather station (3,800′) reaching a high of 30 degrees.   Overnight, another front impacted our area with temperatures dipping slightly and east winds increasing quite dramatically around 6pm with Sunburst measuring a 7-hour period of sustained winds in the 40’s and gusting into the 70’s mph from the east.

You guessed it, another storm day on tap for our region today!   Temps should cool slightly (mid-30’s at 1,000′) from yesterday bringing the rain/ snow line back down somewhere closer to 1,500′.   Expect another .5 € of water and winds again from the east in the 20 €“ 45mph range at ridge top level.  

Looking out toward the weekend we may see a break in this overall pattern and see some clearing with slightly cooler temperatures by Saturday and Sunday.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  40  0 .7   79  
Summit Lake (1400′) 38    0  .1 27  
Alyeska Mid (1700′)  35  0  .5  72

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  27 E   26    74
Seattle Ridge (2400′)  30 E    32* 75*  

*Winds reporting since 3pm

Observations
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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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