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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, January 8th, 2020 - 7:00AM
Expires
Thu, January 9th, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger remains MODERATE above 1,000′. Triggering a slab avalanche up to 3 feet thick is still possible due to old weak layers that sit 1-3′ below the snow surface. Additionally, fresh shallow wind slabs may form and be triggered as an increase in westerly winds along ridgelines is expected today. As always, watch your sluff on steep slopes, give cornices a wide berth and limit exposure under glide cracks.

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Wed, January 8th, 2020
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
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

After five days of cold, clear and calm weather, this sixth day should bring some slight changes. A bump in westerly wind is expected along ridgelines, discussed below, and even colder temperatures are being reported this morning in valley bottoms (around -15F) and not expected to rise more than a few degrees.

Despite the slight bump in winds, we do remain in a generally persistent weather pattern. This is keeping our main avalanche concern focused on triggering a large slab avalanche that breaks deeper in the snowpack. If you’ve been following along for the past week, you’ll know there is a layer of buried surface hoar 1-3′ deep which was responsible for three snowmachine triggered slabs in Seattle Creek drainage last Friday and a layer of faceted snow over a crust, which was the culprit in the Magnum avalanche from Sunday. There have been no avalanches reported in the past two days. Remember you can view all the reported avalanches on our avalanche list.

Avalanche science tells us with more time and cold temperatures, the likelihood for triggered these slabs should be decreasing, but we still need to keep this possibility front and center. Things to keep in mind:

  • Signs of instability are not likely to be present before a slope releases.
  • Thin areas are likely to be the trigger spots. These can be tough to see from the surface but common places are, on top of rollovers, near rocks protruding and areas that have seen wind scouring.
  • Tracks on a slope doesn’t mean it’s safe. This is the scenario that the 3rd or 10th person could trigger an avalanche.
  • Remote triggering a slab is possible, meaning from the top, sides or below.

As we’ve been saying, good travel habits help stack the odds in our favor. Exposing one person at a time, watching our partners, having escape routes planned and considering the consequences if the slope does slide.

A closer look at the skier triggered avalanche on Sunday 1/5/20 on the west face of Magnum. 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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
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

If you are headed out today, keep a close eye on any winds that are impacting your area. West winds are expected to rise to 10-15mph and possibly 20mph in places with gusts to 30mph. With such loose snow on the surface, it won’t take much wind to move the snow around. Any fresh wind slabs found could be easily triggered. Even a small wind slab in high elevation steep terrain can cause problems if it knocks one off their feet.

Loose snow sluffs:  The surface snow is becoming looser and looser by the day with the cold temperatures. Sluffs are getting larger because of this and gaining volume in longer sustained slopes. Keep an eye on your sluff.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks:  Glide cracks are continuing to slowly open around the area. There are several around the Cornbiscuit ridge and in the Gold Pan zone in upper Bertha Creek along with others sprinkled about. Watch for cracks and limit time spent underneath them as they could release into a dangerous glide avalanche at any time.

Cornices:  Cornices are looming along ridges. Be sure to give them plenty of space and limit your exposure when passing beneath them.

Weather
Wed, January 8th, 2020

Yesterday:  Another COLD!, clear and calm day as one of our observers stated yesterday. Temperatures were -10 to -5F along ridgetops and -20 to -10 in valley bottoms. Winds did pick up slightly along ridgetops overnight from the West to near 10mph with gusts near 20mph.

Today:  Clear skies and slightly colder temperatures are on tap today. Already this morning valley bottoms sit around -15F and ridgetops around -10F; these are only forecast to rise a few degrees through the day. Ridgetop westerly winds should see a bump into the 10-15mph range with gusts to 30 midday before quieting down again this evening.

Tomorrow:  The stagnant cold air mass over us looks to remain in place into the weekend. However, a pattern shift is being advertised by the NWS beginning later this weekend for next week. Hence, several more cold days with lights winds are expected.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) -9 0 0 39
Summit Lake (1400′) -16 0 0 14
Alyeska Mid (1700′) -4 0 0 35

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -6 W 7 23
Seattle Ridge (2400′) -8 N 3 9
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Updated Fri, May 01st, 2020

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

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Closed as of May 1. Thanks for a fun, safe season!
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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.