Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, April 5th, 2018 - 7:00AM
Expires
Fri, April 6th, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is CONSIDERABLE on all aspects and elevations, but may increase to HIGH by early evening. Triggering a fresh storm slab 1-3′ thick is likely on slopes steeper than 35 degrees. Natural wet-loose avalanches are possible in the afternoon with daytime warming and may become more likely on Southerly aspects if the sun comes out today. If you see natural avalanche activity this is a sign the danger is increasing and it will be important to avoid all avalanche terrain including runout zones. In addition, keep in mind there is still a chance for triggering a deeper avalanche 3-4+’ thick in older layers of the snowpack.  

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Thu, April 5th, 2018
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
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. Small avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become large enough to bury, injure, or kill people, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

A storm moved through our region yesterday bringing strong Easterly winds and dumping 1-2 feet of new snow across our region. Girdwood was favored with Alyeska reporting 18” at midway and 24” at the top. On the Northside of Turnagain Pass totals were estimated in the 12”-18” and observers reported around 8-10” by 6pm last night at Sunburst. Don’t forget these storm slabs were formed by strong Easterly winds and slabs could be 2-3 feet thick on leeward features in the alpine, especially in Girdwood Valley. This new snow fell on variable surfaces including a slick melt/freeze crust on Southerly aspects and patches of loose faceted snow and crusts on other aspects.  Either way bonding will be poor and triggering a storm slab is likely today. The size of the slab will depend on the size of the terrain. An observer at Tincan reported lots of human triggered storm slabs and loose snow sluffing in the trees throughout the day. Careful snowpack evaluation and caution route finding will be essential. Warming in the afternoon may increase the likelihood for triggering storm slabs. If you see any natural avalanche activity this is a sign to avoid all avalanche terrain and stick to flat mellow terrain well away from the runout zones of larger slopes. 

  • Turnagain Pass: 10-18”  (~1.0” SWE)
  • Summit Lake: 4-6” (0.3” SWE)
  • Girdwood -Alyeska midway: 18” (1.4” SWE) 
  • Portage – Bear Valley: 14” (1.3” SWE)

Turnagian Pass Snowstake at the DOT RWIS weather station reported around ~15″ of new snow yesterday.

 

Observers yesterday on Sunburst reported 9″ of new snow by 6pm. This was quite a bit less than observations from Tincan. 

Avalanche Problem 2
  • Wet Loose
    Wet Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. Small avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become large enough to bury, injure, or kill people, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

SPRINGTIME WARMING: Daytime temperatures are expected to increase to the mid 30F’s near ridgetops and low 40F’s near sea level as snow and wind taper off in the afternoon. If the sun appears today or any radiation through cloud cover – this will increase the potential for natural wet-loose avalanches later in the day. Southern aspects will be more likely if the sun come out, but all aspects are suspect if clouds trap the heat. Lower elevations such as Placer Valley and Portage may see more natural activity on lower elevations slopes, especially in channeled terrain. Pay attention to how the snow changes throughout the day. Heavy moist snow and rollerballs will be your first clue the snow is changing. Any natural avalanche activity will be an obvious sign the snowpack is becoming more dangerous and it will be important to adjust your plans. Although it’s not expected, there is potential for a storm related avalanche to trigger a deeper more dangerous avalanche. More on this below.

 

Additional Concern
  • 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

This new snow fell onto a snowpack with poor structure and several weak layers buried 2-4’ below the old surface. Little is known about how the snowpack is adjusting to its new load, and if one of these older weak layers, facets and buried surface hoar, could wake up today.  This is an additional reason to avoid being on or under any larger slopes. Thin snowpack zones such as the Girdwood Valley and the South end of Turnagain Pass are more suspect for this structure, as well as some Northern and Easterly slopes with a generally thinner pack. Trigger points in this situation are often in thinner areas near rocks, but it is also possible to trigger this avalanche problem from areas along ridges. 

This is a snowpit from yesterday on Sunburst and shows the weak interface between the new snow and old snow as well as several older weak layer buried a few feet below. 

Weather
Thu, April 5th, 2018

Yesterday 1-2 feet of new snow fell across our region and strong Easterly ridgetop winds averaged around 25mph with gusts in the mid 40’s mph. Temperatures at 3000′ remained 20F and temperatures at 1000′ bumped in the low 30F’s mid day, but all precipitation remained snow to sea level. The heaviest snow fell yesterday afternoon and early evening becoming light overnight.  

Today skies will be overcast in the morning becoming mostly cloudy later in the day and partly cloudy by this evening. Precipitation is expected to taper off this morning. Easterly winds will be 15-25mph this morning and decrease this afternoon becoming light and variable by early evening. Daytime temperatures may reach the mid 30F’s near ridgetops and low 40F’s at sea level. Overnight temperatures are expected to drop into the low to mid 20F’s.  

Scattered snow showers are possible on Friday, but not much accumulation is expected. Daytime highs will be in the upper 30F’s and overnight lows to drop in the 20F’s. Winds will be light and variable. Saturday could be our warmest day this spring with highs in the 40F’s and partly cloudy skies.  

*Center Ridge Snotel reported 0.4″ SWE and has been under reporting SWE last few storms. Was estimated  Snow Water  Equivalent  (SWE)  to be around 1.0″ based on the hieght of new snow of 12″.    

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   12   *1.0   85  
Summit Lake (1400′) 27   6   .3   37  
Alyeska Mid (1700′) 28   18   1.35   84  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18   ENE   24   48  
Seattle Ridge (2400′) 23   ESE   17   39  
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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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