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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
Sun, January 19th, 2020 - 7:00AM
Expires
Mon, January 20th, 2020 - 7:00AM
Forecaster
Ryan Van Luit
The Bottom Line

A LOW avalanche danger exists in the Turnagain Pass area and could rise to MODERATE late tonight with new snow and wind moving in. In exposed steep terrain with wind affected snow, isolated wind slabs exist and may release under human trigger.  Additionally, sluffs could easily be initiated and gain volume and momentum on steep sustained slopes and chutes. As always, limit exposure under glide cracks and give cornices a wide margin.

SUMMIT LAKE: This region is just out of our advisory area to the south. The snowpack is shallow, composed of several weak layers, and experienced more wind effect and wind slab development. Extra caution is advised for triggering a slab avalanche.

**Snowfall is expected to begin tonight, with up to a foot of new snow falling in the high terrain by Monday. If the storm verifies, this will increase the avalanche danger for Monday, Martin Luther King Jr. Day. 

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Sun, January 19th, 2020
Alpine
Above 2,500'
Low (1)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Low (1)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
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

Although the region is forecast to see some snow tonight, this morning is the 17th day of the January drought. During this dry spell, winds have been generally northwesterly and impacting ridgelines and peaks north of Girdwood, through Turnagain Arm and Portage Valley and south of Johnson Pass. The heart of Turnagain Pass has been spared much of the wind.  With that said, it’s possible that in the last week, wind slabs have formed over weak snow. With the variable wind directions in the region, it’s difficult to predict the aspect these wind slabs may be found, so remain aware.  As always good travel habits are good to keep.

Looking ahead for tomorrow, the new snow will be falling onto a variety of surfaces. This includes, harder wind-packed snow and wind crusts at higher exposed elevations, but predominantly it will fall on very weak sugary snow at all elevations. Bonding with the old snow surface is expected to be poor. Slopes seeing up to a foot of new snow with some wind loading will be prime to avalanche. Stay tuned and be sure to check tomorrow’s forecast!

View toward Kiskstep Mountain from Sunburst ridge near Taylor Pass.  Zoom in for signs of wind effected surface.  1.18.2020  Photo: Heather Thamm

 

Wind slabs on weak snow:  If you’re considering steeper and higher elevation terrain, remain aware of wind affected snow forming slab character. In wind effected areas, look for pockets of pillowed snow, and remain aware of hollow feeling snow. If you experience red flags such as whumpfing (collapsing of the snowpack), or shooting cracks, it’s prudent to adjust your route. Even a small wind slab can have high consequences if it knocks a person off their feet and down a rocky slope or over a cliff.

Loose snow sluffs:  The surface snow is so loose and faceted it’s very easy to initiate a sluff in steep terrain. They can be heavy and gain more volume than one might expect. If heading to steep chutes or slopes, sluffing should not be underestimated.  Right now, this type of avalanche is predictable in steep terrain, making it easier to avoid by either sticking to lower angle slopes (less than 35 degrees), or by consistently skiing off fall line to avoid entrapment.  This short paper is worth a read if you’re interested in the topic.

With recent surface conditions, a rider may easily trigger loose surface facets in steep terrain.  These sluff avalanches may quickly gain both volume and momentum.  1.18.20  Photo:Eric Roberts

Glide cracks:  Glide cracks continue to widen throughout the region. They’re unpredictable so it’s recommended to limit exposure under them as they can release at any time.

Cornices:  We’ve had no reports of recent cornice failure, but they’re large and overhanging.  It’s good travel practice to give cornices as much space as is reasonable.

Weather
Sun, January 19th, 2020

Yesterday: Mostly sunny skies with light easterly ridgetop winds.  Temperatures were near 0°F in valley bottoms and around 14°F at the higher elevations.  Zero precipitation.

Today: Clouds have moved in ahead of a low-pressure system from the Gulf. East ridgetop winds should be increasing slightly to 10-20mph later this afternoon and overnight.  Temperatures will be on rise and expected to reach 20°F at all elevations. Between 4-8″ of low density snow (to sea level) is forecast for tonight with temperatures in the low 20’s.

Tomorrow:  Cloudy skies with 2-4″ of snow possible as the system exists the region.  Temperatures at sea level reaching near 25°F. Expect east wind 5- 15 mph along ridgelines during the day.  The peak of the snowfall looks to be very early Monday morning with winds remaining moderate, in the 15-25mph range.  Total storm snowfall by Monday evening should be close to a foot in the Alpine and a bit less in the parking lots.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 8 0 0 36
Summit Lake (1400′) 2 0 0 15
Alyeska Mid (1700′) 6 0 0 36

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14 VAR 7 12
Seattle Ridge (2400′) 12 N 2 5
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Riding Areas
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

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
Closed

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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.