Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 19th, 2022 - 7:00AM
Expires
Sun, February 20th, 2022 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ today. A widespread natural avalanche cycle yesterday, which was responsible for multiple highway closures throughout Southcentral AK, is a wake up call that dangerous avalanche conditions exist. Conservative decision-making and cautious route finding are recommended today so we can give the snowpack time to adjust to the new load. Human triggered avalanches up to 2′ deep are likely in wind loaded areas and natural avalanches are possible. The sun could play a role in triggering natural avalanches today on east, south, and west facing slopes. Below 1000′ the avalanche danger is MODERATE.

SUMMIT LAKE/LOST LAKE/SNUG HARBOR: The avalanche conditions are dangerous across the Kenai peninsula, where new snowfall this week has caused many natural avalanches and the potential for human triggered avalanches today is high. The snowpack needs time to adjust to the new snow load from this week and we recommend cautious decision-making today.

Special Announcements
  • Chugach State Park – Multiple large natural avalanches were observed in the Anchorage Front Range yesterday and the potential for human triggered avalanches today is elevated. See observations for more details (here, here, here).
  • Hatcher Pass – The road to Hatcher Pass remains closed and avalanches conditions are very dangerous. See the Hatcher Pass avalanche forecast for more details.
  • We’ve posted a deeper look into two near-misses from this season in our latest News Post. There are some valuable lessons to be learned from both incidents, and it is absolutely worth the time to read through the details.
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Sat, February 19th, 2022
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

After several weeks of nearly continuous snowfall, the last pulse of precipitation that fell overnight Thursday and into Friday morning was enough to push the snowpack over the edge and cause a widespread natural avalanche cycle. The most notable avalanche was the one that closed the Seward highway just north of Girdwood for the first half of yesterday but there were many others throughout the area which are clear indicators of dangerous conditions. We received too many avalanche observations yesterday to post them all, but here is a selection of the recent avalanche activity with links to the observations where you can find more detail.

  • Girdwood area – A large natural avalanche released in the early morning hours yesterday from Penguin ridge just north of Girdwood and covered the highway in 10-15′ of debris. We are still sorting out the exact details of this avalanche activity but it appears that an avalanche initiated in the new wind loaded snow and was able to step down into deeper weak layers and create a wide propagating avalanche. It is not clear how large the natural avalanche was that covered the highway versus the additional avalanches that were released by hazard reduction efforts of the DOT during the day yesterday.
    Avalanches along the Seward highway just N of Girdwood with very wide propagation which stepped down to deeper weak layers in some areas (details here). Note that this photo includes the natural avalanche that struck the road as well as the avalanches that resulted from hazard reduction work of the DOT and it is difficult to tell which is which. Photo 2.18.22

Three more natural avalanches in California Creek that released mid-slope (roughly 2500-3000′) and had relatively wide propagation. Photo 2.18.22

  • Turnagain Pass – Those lucky few who were on the right side of the road closure and made it up to Turnagain Pass yesterday reported several wind slab and storm slab avalanches. These include avalanches that were likely triggered by wind loading along ridgelines, some storm slabs that were reactive to human triggers in protected areas, and two avalanches on Lipps (photo below) that appear to have been related to the sun creating wet loose avalanches that triggered a storm or wind slab below. See observation here for photos of smaller avalanches on Tincan and Seattle Ridge.

Two large natural avalanches on the W face of Lipps that appear to have been triggered by the sun releasing wet loose snow or rollerballs coming down from above (details here). Photo 2.18.22

Avalanche Problem 1
  • 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

Today looks like a beautiful day to be in the mountains and after a few weeks of mostly stormy weather folks are probably chomping at the bit to take advantage of the new snow and visibility. However, we need to consider the widespread natural avalanche cycle that happened over the past 36 hours and the fact that dangerous conditions remain throughout the forecast area. A variety of different types of avalanches were reported yesterday and we recommend careful evaluation of the terrain and snowpack as well as conservative decision making if you get into the backcountry today.

The primary avalanche problem today will be wind slabs up to 2′ deep that were created overnight Thursday and early Friday morning. These are most likely to be found at upper elevations along ridgelines, cross loaded gullies, and convex rollovers. In addition, observations from yesterday showed that storm slabs are possible to trigger in wind sheltered areas (details here). With the warm temperatures since the storm ended we expect that the new snow is starting to bond to the old snow surface and the chances of triggering storm snow avalanche are decreasing, but the potential for persistent weak layers underneath the new snow could make these avalanches last longer than normal (see problem 2 for more details). Quick stability tests like hand pits and using small test slopes to check for shooting cracks are effective ways to assess how well the new snow is bonding to the old snow surface.

The sun is finally starting to play a role in the avalanche conditions, with the potential for solar triggered wet loose avalanches to release a larger storm or wind slabs on east, south, and west aspects. We saw an example of this on Lipps yesterday where two avalanches were probably triggered by loose wet snow coming down from above (details here). Be aware of the terrain above you if the sun comes out today because it is possible for natural avalanches to be triggered from solar warming.

Snowpit yesterday from Seattle Ridge at 2900′ showing potential for avalanches about 1-2′ deep at the interface between the new snow and old snow surface (ob here). Photo 2.18.22

Avalanche Problem 2
  • 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

The wide variety of avalanches observed yesterday have us scratching our heads a bit about exactly what weak layers were responsible for this widespread activity. In areas with a thinner snowpack we know that there are buried facets from November above a strong crust which has the potential to create very large avalanches and likely played a role in the avalanches on Penguin Ridge that struck the highway. These layers are less likely to trigger in areas with a deeper and stronger snowpack but the large avalanches yesterday are a scary reminder that this deeply buried weak layer exists throughout the area.

Other weak layers exist in the upper snowpack that seem to be highly variable in distribution across the forecast area and have the potential to create wide propagating avalanches, such as the natural activity in California Creek yesterday (see recent avalanches). Our uncertainty is high about the distribution of weak layers because avalanches appear to have released on different layers in Girdwood versus Turnagain Pass yesterday. We recommend carefully evaluating the snowpack structure before entering avalanche terrain and keeping an eye out for weak layers that could cause avalanches to propagate widely.

Weather
Sat, February 19th, 2022

Yesterday: Overcast to broken cloud cover with no new snow accumulation during the day. Temperatures were in the 20s at ridgetops and 30s below treeline. Winds were mostly light with some stronger gusts along upper elevation ridgelines into the mid 20s.

Today: It looks like a beautiful day in the mountains today. Light winds in the 5-15 mph range out of the NW, mostly to partly sunny, and temperatures in the 20s to 30s. No new snowfall is expected.

Tomorrow: Sunday looks like another day of calm and relatively clear weather before another round of snowfall could move into the area on Monday afternoon. We may see high clouds starting to build on Sunday ahead of the arrival of the next low pressure system.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 0 0 95
Summit Lake (1400′) 28 0 0 46
Alyeska Mid (1700′) 32 0 0 NA

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 W 9 27
Seattle Ridge (2400′) 24 W 4 12
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/11/22 Turnagain Avalanche: Cornbiscuit and Magnum west faces
05/07/22 Turnagain Observation: Granddaddy
04/29/22 Turnagain Observation: Sunburst wx station
04/28/22 Turnagain Observation: More Turnagain Pass/Summit Lake wet slab activity
04/27/22 Turnagain Observation: Magnum
04/27/22 Turnagain Observation: Girdwood/Summit/Turnagain Road obs
04/24/22 Turnagain Avalanche: Seattle Ridge – large glide avalanche on Repeat Offender path
04/24/22 Turnagain Avalanche: Seattle Ridge uptrack
04/24/22 Turnagain Observation: Pastoral
04/24/22 Turnagain Observation: Sunburst
Riding Areas
Updated Fri, May 13th, 2022

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 as of May 1 per Forest Plan.
Placer River
Closed
Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage
Closed
Closed as of April 1st per Forest Plan.
Turnagain Pass
Open
Open. Extended opening through May 31.
Twentymile
Closed
Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake
Closed
Closed as of May 1 per Forest Plan.
Lost Lake Trail
Closed
Closed as of May 1 per Forest Plan.
Primrose Trail
Closed
Closed as of May 1 per Forest Plan.
Resurrection Pass Trail
Closed
Closed as of May 1 per Forest Plan.
Snug Harbor
Closed
Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor
Closed
Closed as of May 1 per Forest Plan.
Summit Lake
Closed
Closed as of May 1 per Forest Plan.

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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.