Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, February 11th, 2018 - 7:00AM
Expires
Mon, February 12th, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is currently MODERATE and expected to rise to CONSIDERABLE  late tonight and tomorrow in conjunction with snowfall and strong wind. For the daylight hours today, wind slabs up to a foot thick along with lingering larger slabs up to 2′ thick will be possible to trigger on slopes with wind deposited snow. Watch for changing conditions and in the event snowfall begins earlier than expected, avalanche danger will begin to rise.

Thanks to our sponsors!
Sun, February 11th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

One more breezy overcast day is on tap before snowfall begins to fall in earnest tonight. We could see light snowfall add a couple inches through the day, but the bulk of the expected storm snow (6-12″) should fall late tonight through Monday morning. Keep in mind, avalanche danger will rise along with snowfall. The new snow will fall on a weak surface and storm snow avalanches should be expected if this storm verifies. 

Prior to tonight’s snow, our main concern for triggering an avalanche remains with slopes that have seen, or are seeing, wind loading. Ridgetop winds have been moderate to strong over the past 48 hours from a generally East direction. These have scoured some ridges and loaded leeward slopes with the existing loose snow available for transport. Small pockets of wind slabs could be triggered on these leeward slopes and these should be relatively easy to identify (smooth pillowed surfaces and stiffer snow over softer snow). More concerning however, is the possibility of finding a wind slab that is sitting on buried surface hoar 1-2′ deep. There are multiple layers of buried surface hoar  that sit in the top 2′ of the snowpack, which may now be overloaded by wind deposited snow. These types of slabs could be larger than expected and break deeper than your ‘typical’ wind slab. If you head out today, watch for how the winds are transporting the snow and avoid wind loaded slopes. Additionally, slabs may range from soft or hard and have the potential to break above you once committed to a steep slope. 

Wind scouring along the South end of Seattle Ridge yesterday, looking SW from the Eddies ridge (photo: Allen Dahl) 

 

Wind transport just above the trees on Eddies (video: Allen Dahl). Winds are not only loading certain slopes and scouring others, but creating wind crusts as well.


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

Our snowpack structure is generally poor and weak snow can still be found in the bottom portion of the snowpack at the higher elevations, above 3,000′. Shallow snowpack zones, such as on the South end of Turnagain Pass, Summit Lake and portions of the Girdwood Valley are more pronounced. Although triggering an avalanche breaking deeper in the pack is unlikely, a chance does remain, as a party found the right trigger spot last weekend in the Twin Peaks area. It is worth keeping this poor structure in mind and considering a conservative approach to avoid large steep terrain with shallow snow cover or exposed rock. 

Weather
Sun, February 11th, 2018

Overcast skies filled the region yesterday with windy conditions near and above the trees. Ridgetop winds averaged 15-25mph with gusts to 40mph from a generally East direction. Temperatures were on the warm side, low 20’sF in the Alpine and 30F at 1,000′. A few flurries fell overnight with around an inch of snow recorded at mid-elevations in Girdwood Valley and Turnagain Pass.

Today, a quick moving warm(ish) storm is moving into the area. Snowfall is expected to be light through the daylight hours, with around 1-3″ accumulation, then intensify this evening through Monday morning, adding another 6-12″. Ridgetop winds are forecast to shift Southeasterly and remain in the 10-20mph range until tonight when they bump up into the 25-35mph range with the heavier snowfall. Temperatures are expected to rise to the mid 20’sF along ridgetops and the mid 30’sF at sea level, this will bring a rain/snow mix to sea level and possibly raise the snow line to ~500′-1,000′.  

Monday, light snowfall is expected as the system moves out with a possible 1-3″ accumulation. Ridgetop winds look to remain moderate to strong with a shift to Westerly bringing cooler temperatures. Storm total by Monday evening is looking to be around 6-12″ of medium density snow at the mid to upper-elevations.  

NWS graphic for the Monday storm:

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27   1   0.06   61  
Summit Lake (1400′) 28   0   0   19  
Alyeska Mid (1700′) 29   1   0.1   52  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21   NE   13   41  
Seattle Ridge (2400′) 25   SE   21   41  
Observations
Recent Observations for Turnagain Pass
Date Region Location
12/08/19 Turnagain Avalanche: Tincan
12/06/19 Turnagain Avalanche: Sunburst
12/04/19 Turnagain Observation: Sunburst
12/03/19 Turnagain Observation: Hippy Bowl
12/01/19 Turnagain Observation: Tincan, All elevations
12/01/19 Turnagain Observation: Tincan
11/30/19 Turnagain Observation: Tincan Treeline Plateau/ Common Bowl/ Ridge
11/29/19 Turnagain Observation: Sunburst Ob #2
11/29/19 Turnagain Observation: Sunburst Ob #1
11/27/19 Turnagain Observation: Tincan
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.

Subscribe to Turnagain Pass
Avalanche Forecast by Email