Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, January 3rd, 2020 - 7:00AM
Expires
Sat, January 4th, 2020 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

A MODERATE avalanche danger exists at and above treeline where it remains possible to trigger an avalanche breaking on a buried weak layer in the snowpack. Loose snow, lingering wind slabs and precarious cornices should also be on your avalanche radar. With several motorized areas opening today, terrain progression and good travel protocol will be the name of the game.

Below treeline the danger is LOW.

Special Announcements

Several areas across the Chugach National Forest open to over snow vehicles today. DOT is still working on plowing roads and parking lots.  Please avoid parking in areas that will impede their progress to clear snow from the NYE storm.  Reference the “Riding Areas” tab on this page for the latest info.

Fri, January 3rd, 2020
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.
Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "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. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Forecasters and observers are continuing to consistently find a layer of buried surface hoar in our snowpack across the advisory area. After the storm on New Years Eve that deposited 12-24”+ of low-density snow, this layer is anywhere from 18” -36” deep. It tends to be shallower on the south end of Turnagain Pass and likely easier to trigger. Triggering an avalanche on this buried surface hoar layer remains a possibility today and may not be prefaced by any red flags. Ask yourself the question: If this slope does slide, what are the consequences?

Clear skies, quality snow and a motorized opener today will have skiers and snowmachiners pushing into new terrain today that hasn’t seen any traffic or slope testers this season. Keep terrain progression on you mind and don’t let your personal human factors get the best of you. Furthermore, expose only one person at a time and be mindful of where you’re at in relation to other groups as you travel through avalanche terrain today.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.
Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "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. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Dry unconsolidated storm snow and cold temps have us thinking about sluff management. Clearing skies yesterday allowed observers to spot a handful of loose snow avalanches in steep terrain, including on the front face of Seattle Ridge. Be mindful and cognizant of consequences if you were to get knocked off your feet by a fast moving sluff in steep terrain.

Wind slabs: Lingering wind slabs from the NYE storm may be found today below ridge lines and in cross-loaded gullies. Additionally, given the low-density surface snow, even light winds yesterday and today (15-20mph) could build fresh wind slabs.

 Cornices: Wet snow and wind in the Alpine during the warm part of Tuesday’s storm added snow/ weight to precarious cornices in the Alpine. Avoid travel on or underneath these backcountry bombs and pay attention to groups traveling above or below you.

Corniced ridge above Sunburst’s SW face yesterday.  photo: Paul Wunnicke

 

Weather
Fri, January 3rd, 2020

Yesterday: Partly cloudy skies and a few hours of instability showers thru Turnagain Pass led to about an inch of accumulation. Temperatures were hovering around 0 degrees F at 1,000’ and winds were generally light, but kicked up from the NE around 2pm where ridgetop locations saw gusts into the 30’s mph.

Today: Partly sunny skies and cold temps are on tap. Temperatures will be in the single digits and winds light from the North with no new precip expected. Isolated areas may see gusty NNE winds as interior high pressure sets up.  Generally the thought is these outflow winds should stay to our east today with the greatest impact to the Copper River Basin and Thompson Pass.

Tomorrow: Mostly sunny skies, light winds and high temperatures that are not likely to climb out of the single digits.  Bundle up, get outside and enjoy that mid-winter light!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6 1 .1 43
Summit Lake (1400′) -1 0 0 15
Alyeska Mid (1700′) 8 3 .41 38

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 0 ENE 11 37
Seattle Ridge (2400′) 4 n/a n/a n/a
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Riding Areas

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.
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