Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, December 30th, 2023 - 7:00AM
Expires
Sun, December 31st, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′ today. Glide avalanches have been releasing at an alarming rate this week and we expect that to continue today. It is important to avoid spending time underneath glide cracks to avoid these large and destructive avalanches. Wind slabs 1-2′ deep on high elevation ridgelines are also possible for people to trigger today. Below 1000′ the avalanche danger is LOW.

Special Announcements

Become a Member in December! The Friends of the Chugach Avalanche Center, our non-profit arm, needs your help to keep our avalanche center running. Note, everyone who donates will be entered to win some awesome prizes at Andrew’s Girdwood Brewery Forecaster Chat on January 19!

Sat, December 30th, 2023
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
Sun, December 31st, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Sun, December 31st, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
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. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. 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

Another glide crack released yesterday in the Crow Creek area of Girdwood. An anonymous observer shared before and after photos with us to confirm the timing. Otherwise we do not know of any recent human triggered avalanches in the forecast area over the past several days.

This avalanche looks small in the photo, but it is likely 3-5′ deep and ran several thousand feet into the valley bottom. Photo from Anonymous 12.29.23

Avalanche Problem 1
  • Glide Avalanches
    Glide Avalanches
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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 number of glide avalanche releases that have occurred in the past week is not normal. Typically we have glide cracks spread across the forecast area for most of the season and they occasionally release at random times, but during the recent cold snap glide avalanches have been releasing daily and they are located nearby many popular travel routes. These include Seattle Ridge and the motorized uptrack, Cornbiscuit, Tincan, Crow Creek area and many more. Glide avalanches are unpredictable and can randomly release even if it doesn’t look like they are currently active.

Due to the widespread distribution of glide cracks and high frequency of releases in recent days, glide avalanches are the primary hazard for travelling in the backcountry today. When glide avalanches release they take the entire snowpack with them, so in Turnagain Pass and Girdwood that means a 4-6’+ deep avalanche that is highly destructive and can runout far into valley bottoms. To avoid glide cracks we recommend carefully inspecting the slopes overhead before setting your skintrack or uptrack. Look for the classic ‘brown frown’ that indicates that the snowpack is sliding down the mountain and leaving a crevasse like crack that extends to the ground. Sometimes the ground surface in the crack is filled in with new snow, which makes identifying glide cracks a little trickier. In this case you can look for a wrinkly texture on the snow surface to indicate where buried glide cracks may exist. The best thing you can do is minimize the amount of time you spend underneath a glide crack.

See how many glide cracks you can ID on Seattle Ridge by zooming in on this photo! Photo Peter Wadsworth 12.22.23

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

Despite the mostly light winds over the past few days there has been enough wind transport on high elevation ridgelines to form fresh wind slabs 1-2′ deep. These will likely be localized to the highest ridges and are probably not big enough to bury a person but could easily knock you off balance in steep terrain. Look for shooting cracks and hollow, drum like snow surfaces to identify areas with recent wind slabs.

Winds are expected to increase Saturday night as a weather system enters the forecast area. If these winds pick up sooner than forecast then fresh wind slabs could start forming at upper elevations, making natural and human triggered avalanches likely. Look for signs of active wind transport along ridgelines to determine if fresh wind slabs are forming in the area you are travelling.

Prior to the last major storm a week ago there was a widespread layer of surface hoar on the snow surface. Based on field observations this week it seems like this layer was mostly destroyed by wind prior to being buried by the snowfall, but it is possible that the surface hoar was preserved in specific areas and could cause an avalanche about 2′ deep at the interface with the old snow surface. Since we have not heard of any reports of avalanches on this layer so far this week we think it is unlikely for a person to trigger. If you are venturing into a new area today you can use a compression test or extended column test to check whether the surface hoar exists in that location.

Dry loose avalanches are very likely on steep terrain today. To avoid being pushed around by loose snow make a plan to manage your sluff prior to entering steep terrain.

Wind affected snow along ridgelines could produce small wind slabs 1-2′ deep today. Photo 12.28.23

Weather
Sat, December 30th, 2023

Yesterday: The weather on Friday was very similar to Wednesday and Thursday, with temperatures ranging from positive to negative single digits F. Due to a temperature inversion it was colder at lower elevations than on the ridgetops. Skies were mostly clear except for a layer of valley fog that covered the lower elevations up to about 1000′. Winds were light averaging 0-5 mph with gusts up to 20 mph in alpine areas.

Today: This will be the last of the clear and cold days for awhile. Temperatures are expected to remain in the single digits F today and rapidly start to climb back towards the teens and low 20s F overnight. Winds will also remain light during the day with averages of 5-15 mph before sharply increasing to averages of 30-50 mph overnight. Along with the increasing temperatures and winds will come a new round of snowfall, which is expected to start around 9 pm and bring 2-5″ of new snowfall overnight.

Tomorrow: Temperatures should be in the teens to 20s F tomorrow, with snow falling down to sea level or possible creeping up to 100-200′. The majority of the snowfall is expected to arrive overnight on Saturday with lingering showers and light snowfall likely on Sunday. The snow total during the day on Sunday is expected to be 3-6″. Winds will be the main story on Sunday, with averages of 20-35 mph and gusts to 50 mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) -2 0 0 77
Summit Lake (1400′) -14 0 0 N/A
Alyeska Mid (1700′) 2 0 0 69
Bear Valley – Portage (132′) -3 1 0.07
Grouse Ck – Seward (700′) -5 0 0 50

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 6 W 7 19
Seattle Ridge (2400′) 5 N 1 4
Observations
Recent Observations for Turnagain Pass
Date Region Location
02/24/24 Turnagain Observation: TinCan Backdoor/ Center Ridge
02/22/24 Turnagain Avalanche: Lynx Creek
02/22/24 Turnagain Observation: Turnagain, Seattle, Mt Ascension
02/21/24 Turnagain Observation: Tincan Trees
02/21/24 Turnagain Observation: Sunburst
02/20/24 Turnagain Avalanche: Tincan
02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
02/18/24 Turnagain Observation: Lynx creek
02/18/24 Turnagain Observation: Tincan Trees
Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.


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.