Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, December 9th, 2020 - 7:00AM
Expires
Thu, December 10th, 2020 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is trending to MODERATE after 2-3′ of snow fell onto a weak surface during the Sunday/Monday storm. Storm slab and wind slab avalanches up to 2′ thick in Turnagain and 3′ thick in Girdwood will be possible to trigger. These could be quite large, be triggered remotely and could propagate across terrain features. It’s a day to watch for signs of instability and take our time easing into the bigger terrain.

SUMMIT LAKE:  The chance for triggering a large avalanche breaking in weak faceted snow near the ground continues in this area due to shallow snowpack conditions. This issue is most likely in the Alpine above 2,500′.

MOOSE PASS to SEWARD:  A Special Weather Statement has been issued for heavy snow in the Southern Kenai Mountains from Moose Pass to Seward. This is outside of our forecast zone, but be aware that avalanche danger will rise in any area receiving heavy snow today.

Special Announcements

Mark your calendars!! You don’t want to miss Forecaster Chat #2 – Persistent Slab and Deep Persistent Slab Avalanches with Aleph Johnston-Bloom – virtual on Zoom.

Thanks to our sponsors!
Wed, December 9th, 2020
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
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
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

It’s been just over a day since the end of the last storm that hit Sunday into Monday, which dropped 2-3′ of new snow. With light snow showers forecast today, possibly adding 3-5 inches and even another 2-4″ tonight, this should not be quite enough to create new avalanche issues in itself and the main concern still lies with the snow that fell early this week.

Large storm slab avalanches are possible. These are in the 1-2 foot thick range depending on the amount of new snow in Turnagain Pass and up to 3′ thick in favored areas in the upper Girdwood Valley where more snow fell. Although we have little information from yesterday, we know these storm slabs were touchy on Monday. This is in large part due to the snow being warmer and heavier as well as falling onto 4-10″ of loose faceting snow with surface hoar on top. In areas up to 2,500′ that loose snow sat on a stout crust. Yesterday, observers in the 2,000-2,500′ elevation band on Seattle Ridge found the storm slabs to be bonding, a great sign, but this isn’t something to assume is happening everywhere just yet. It’s a day to really watch for RED FLAGS:

  • Any whumpfing in the snowpack?
  • Cracks that shoot out in the snow around you?
  • If yes, then the new snow is still unstable and sticking to low angle slopes and the flats is key.

Wind Slabs:  Ridgetop winds have been steady on Sunburst right around 15mph with gusts into the 20’s mph, from the east. This is just enough to keep any snow that is still available for transport along ridgelines moving and fresh wind slabs may be found in the Alpine. Add to that, we should be on the lookout for any older wind slabs from the Sunday/Monday storm in the Treeline and Alpine elevation bands.

Cornices:  Although visibility has been difficult, we know cornices have grown and could still be teetering on the brink. Give them a wide berth as they can now easily break further back than we might expect. As seen last week, they can also trigger an avalanche below, creating a bigger problem if a person is involved.

 

Seattle Ridge at 2,000′: There is around 20″ (50cm) of settled storm snow from the Sunday/Monday storm. This fell on top of another foot (30cm) of older snow that had become faceted with the cold and clear weather during the end of last week. No signs of instability were seen in this pit yesterday (12.8) and the crust, formed when rain fell up to 2,500′ on 12.1, sits ~32″ (80cm) below the surface. Photo: Brian Murphy

 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

That old October snow near the ground is getting more and more buried with the snowy weather. This is great news! It helps to squash the layer and keep our weight far above it; in essence making it so triggering a deep persistent slab is much less likely. That said, hitting a thin area in the snowpack or traveling in areas with an overall shallower snowpack (around 3-4′) is still concerning for triggering a large slab. The south end of Turnagain Pass through Silvertip, Johnson Pass and Summit Lake all have slopes without as much snow as Turnagain or Girdwood. Heads up in these areas and remember to feel/listen for whumpfing and watch those shallow slopes.

An example of an area that is still suspect for triggering a deep slab. This is pit is from Tenderfoot Ridge in the Summit Lake area (2,500′ elevation) and shows the weak facets at the bottom of the snowpack. 12.8.20. Photo: Nick D’Alessio

Weather
Wed, December 9th, 2020
Yesterday:  Light snow flurries were over the area until late morning then skies began to break slightly. Only 1-3" of new snow fell in those morning hours. Ridgetop winds have been moderate (1-15mph) from the east with a 2 hour period at noon of 20's mph gusting up to 49 on Sunburst. Temperatures were near 30F during the day before falling overnight and sit in the teens and 20'sF this morning. Today:  Light snow showers will pick up again today adding 3-5" over the Girdwood and Turnagain Pass area before another 2-4" is forecast to fall tonight. Ridgetop winds are expected to remain from an easterly direction in the 15-25mph range. Temperature should remain near 30 at sea level and in the 20's along the ridgelines. Tomorrow:  Some lingering snow showers over the region before skies are expected to start clearing for a day or so. Ridgetop winds look to be light and variable while temperatures should continue to drop into the teens in most locations. PRECIPITATION 24-hour data (6am - 6am)
Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 28 0 0 66
Summit Lake (1400') 18 1 o.1 26
Alyeska Mid (1700') 29 3 0.2 64
RIDGETOP 24-hour data (6am - 6am)
Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20 E 15 49
Seattle Ridge (2400') 25 SE 6 20
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/18/21 Turnagain Observation: Tincan Ridge
04/30/21 Turnagain Observation: Sunburst
04/27/21 Turnagain Observation: Tincan Ridge
04/26/21 Turnagain Observation: Magnum
04/25/21 Turnagain Observation: Sunburst
04/24/21 Turnagain Observation: Airplane obs
04/24/21 Turnagain Observation: Corn biscuit
04/23/21 Turnagain Avalanche: Lynx Ck Drainage
04/23/21 Turnagain Avalanche: Sunburst
04/23/21 Turnagain Observation: Center Ridge Turnagain pass
Riding Areas
Updated Tue, June 01st, 2021

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
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

Subscribe to Turnagain Pass
Avalanche Forecast by Email

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.