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Sun, December 29th, 2019 - 7:00AM
Mon, December 30th, 2019 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is expected to rise to CONSIDERABLE today above 1,000′ with warming temperatures, new snow and strong wind moving in. Wind slabs 1-2′ thick will be likely to trigger on slopes seeing active wind loading. Additionally, human triggered slabs 12-16″ thick are possible on slopes out of the wind and in the trees. Natural avalanches in the Alpine and cornice falls are possible.

*Low elevations: There is a chance an avalanche from above could send debris below 1,000′ and hit summer trails.

Special Announcements

Chugach State Park: We’ve had a few reports of touchy wind slabs in the Chugach State Park. With strong winds forecast for this zone, expect a rising avalanche hazard.

Sun, December 29th, 2019
Above 2,500'
3 - Considerable
Avalanche risk
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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. Dangerous avalanche conditions. 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.
Recent Avalanches

There were two skier triggered slab avalanches reported yesterday. One was just south of the forecast area in the Summit Lake zone on Tenderfoot ridge. The slab was triggered by the second person on the slope and in the steeper terrain on the southwest aspect of Tenderfoot. The person was caught and carried an estimated 50 yards, lost a pole and injured their leg. One dog was fully buried and able to pop itself out quickly. The slab was relatively small, 6″ deep and around 20-30′ wide, yet once it released moved very quickly and entrained more loose snow on the descent, which picked up speed and volume. The report can be found HERE.

The second slide was on the east face of Seattle Ridge after dark. This avalanche was thought to be a fresh very soft wind slab from the increase in winds in the afternoon, around 8″ thick. The skier saw the slab fracture and spiderweb then was able to ski to the side, no one was caught. The slide was on or near the Repeat Offender slide path. Details are still coming in.

Additionally, one group on the nothwest end of Tincan found several wind slabs (did not slide) and one large whumpf near treeline. They modified their route after seeing these signs of instability. Their report can be found HERE.

*A big thank you to everyone for taking time to submit these, and all, observations. We are glad everyone is ok and hope the injured skier’s leg heals soon.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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

A change in weather has arrived. Temperatures have increased, and will continue to increase today through tomorrow. Additional snowfall is headed our way- 4-8″ today followed by 5-10″ tonight. And lastly, winds are on the rise and should blow 20-40mph with gusts over 60mph along ridgelines. What this all means is a rise in avalanche danger.

Wind slabs will be the most likely avalanche to encounter through the day and storm slabs could begin to form with warm temperatures and additional snowfall. With plenty of light snow on the surface available to be transported, wind slabs are likely to be found near ridgelines and in cross-loaded gullies; even without new snow. They may also be found in other places winds are/or have been loading slopes, including exposed areas in the treeline band. Watch for wind patterns and feel for stiffer snow over softer snow. Look for cracking in the snow around you and whumpfing (collapsing) in the snow. They are all Red Flags you’ve found an unstable slab.

In areas out of the wind, the fluffy light snow many folks have been enjoying is settling and becoming denser with the warming temperatures. This is creating a potential slab avalanche problem not associated with wind. With a known layer of buried surface hoar and older weak snow 12-16″ below the surface, avalanches breaking in these weak layers could produce slabs up to 2′ thick with additional snow.

Cornices:  New sticky warm snow along with wind are likely to build upon the existing cornices. Natural cornice falls are possible. This is a day to avoid being under them and use very careful travel techniques along ridgelines.

Active wind transport just beginning along Seattle Ridge yesterday and filling in a recent skin track.


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

It has been almost two weeks since the last glide avalanche was reported and over a week since we’ve seen cracks actively opening. With all the new snow and winds, many cracks are now obscured and it’s a difficult task to assess their movement. That said, keep your eyes out for any brown cracks and if you see one, limit your time under it.

Sun, December 29th, 2019

Yesterday:  Partly cloudy to overcast skies were over the region. Light snow showers in the evening have added a trace to 2″ snow to sea level. Ridgetop winds were light and westerly until around 2pm when they switched around to the east and increased into the moderate range (10-20mph) with stronger gusts. Winds have been steadily blowing overnight. Temperatures have risen dramatically due to the approaching low-pressure and sit in the mid teens along ridgetops, 20-25F near 1,500′ and in the teens again at sea level.

Today:  Stormy weather with rising temperatures is on tap. Snow should start falling later this morning, adding 4-8″ of light to medium density snow by this evening. Overnight another 5-10″ could fall. Snow is forecast to turn to rain below 500′ tonight. Ridgetop winds will continue from the east 20-40mph with stronger gusts. Temperatures look to rise to the mid 3o’sF at sea level tonight and into the mid 20’sF along ridgelines.

Tomorrow:  Warm air will continue to stream in and could bump up the snow line as high as 1,000′. Snowfall tomorrow looks to taper off by late morning before another front moves in Monday night. Stay tuned, this is a very active weather pattern we are in!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 17 1 0.1 36
Summit Lake (1400′) 10 0 0 12
Alyeska Mid (1700′) 15 1-2 0.2 30

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13 NE 12 45
Seattle Ridge (2400′) 10-15* SE* 10* 24*

*Winds around 4pm yesterday look to have blown the rime off the wind sensor. The temperature is estimated from using the current temperature readings (the hourly temperature data isn’t displaying and we are working on this).

Recent Observations for Turnagain Pass
Date Region Location
11/16/23 Turnagain Observation: Tincan Common
11/14/23 Turnagain Observation: Sunburst/Magnum
11/14/23 Turnagain Observation: Seattle Ridge
11/13/23 Turnagain Avalanche: Tincan Trees
11/12/23 Turnagain Observation: Sunburst
11/12/23 Turnagain Avalanche: Goldpan – avalanche
11/11/23 Turnagain Observation: Tincan Common
11/11/23 Turnagain Observation: Taylor Pass – Sunburst
11/10/23 Turnagain Observation: Tincan
11/10/23 Turnagain Observation: Tincan Trees
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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.