Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, December 22nd, 2023 - 7:00AM
Expires
Sat, December 23rd, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger will start out MODERATE and rise to CONSIDERABLE above 2500′, depending on the timing of the incoming storm system. Increasing winds throughout the day will form wind slabs 1-2′ deep at upper elevations in exposed terrain. If you see active wind transport or observe wind slabs forming that is a sign that the danger is increasing and natural and human triggered avalanches are becoming more likely.

Below 2500′ the avalanche danger is MODERATE. Wind slabs are possible later in the day at the upper end of this elevation band. A layer of weak snow buried 3-5′ deep also exists which is unlikely to trigger but could cause a very large avalanche.

Summit Lake: In areas with a thinner overall snow depth, like Summit Lake, the potential to trigger a deeper avalanche on a buried weak layer is higher. Based on avalanche activity in the past week it seems like the Summit Lake area snowpack is significantly weaker compared to Turnagain Pass.

Fri, December 22nd, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Sat, December 23rd, 2023
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
Avalanche risk
Sat, December 23rd, 2023
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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

The majority of avalanche activity observed within the forecast area over the past several days of clear weather have been dry loose avalanches releasing in very steep terrain or small storm slabs releasing at the interface with the old snow surface. However, there are some notable outliers on the periphery of the forecast area in the upper elevations of Girdwood Valley (see ob here). The largest of these outlier avalanches released at high elevation around ~5,000′ on NW aspects (see problem 2 for more information).

Small storm slab and dry loose avalanche activity in very steep terrain in Seattle Creek area. Photo 12.21.23

Massive avalanche crown in the Upper Milk Glacier area near Crow Pass. Possibly due to a layer of facets deep in the snowpack from early season storms at upper elevations. Photo George Creighton 12.21.23

Avalanche Problem 1
  • 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

We are gaining a whopping 3 seconds of daylight today, and along with the return of the sun comes the return of stormy weather. Cloud cover, wind, and snowfall will increase throughout the day as a storm system enters the forecast area. Wind speeds are expected to increase from averages of 5-15 mph this morning to 15-25 mph this afternoon to 40-60 mph this evening.

Given the soft snow currently sitting on the surface, the increasing winds will rapidly build wind slabs in exposed areas and will make human triggered and natural avalanches 1-2′ deep possible. The likelihood of triggering a wind slab will depend on the timing of the incoming storm. The easiest way to identify areas where wind slabs are forming is to watch for plumes of snow being transported along ridgelines and feel the snow surface as you approach wind exposed areas. Feeling firm and hollow snow on the surface, seeing shooting cracks on steep features, or triggering small avalanches on test slopes are strong indicators that you are entering an area that could produce a wind slab avalanche.

In sheltered areas dry loose avalanches are likely in steep terrain and we recommend having a plan to manage your sluff before entering steep terrain.

Dry loose avalanches in the foreground and the upper Girdwood Valley covered in a blanket of snow, waiting to be blown around by the incoming winds! Photo Peter Wadsworth 12.21.23

 

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

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

We are continuing to monitor the layer of facets over the Thanksgiving crust, which is now buried 3-5′ deep in the majority of the forecast area. Recent observations from Turnagain Pass indicate that the layer remains stubborn to trigger and we are not aware of any human triggered avalanches on this layer in the last two weeks. However, in areas with a generally thinner snowpack, like Crow Creek in Girdwood and closer to Summit Lake, there have been observations of large natural avalanches during the storm cycle early this week. In these areas triggering a very large persistent slab avalanche 3-5′ deep is more likely and we recommend sticking to lower angle terrain if you want to avoid this problem.

We have very limited information about higher elevation terrain above ~4,000′ and there were several large avalanches observed at these upper elevations in Girdwood Valley yesterday.  These avalanche likely released earlier this week during the last period of snowfall. It is possible that there are weak layers near the base of the snowpack from early season snowfall that exist at these upper elevations but do not exist in the majority of the forecast area. As always, we recommend approaching new terrain cautiously and evaluating the snowpack before committing to steep terrain, especially in areas on the margin of the forecast zone where information is sparse.

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

Glide avalanches continue to release and new glide cracks are opening up across the forecast area. It is important to be aware of any glide cracks above you and try to minimize exposure time underneath them. These avalanches release spontaneously and can be very large and destructive.

Weather
Fri, December 22nd, 2023

Yesterday:  Mostly clear skies with varying degrees of valley fog was seen across the region. Ridgetop winds were light from the west. Temperatures were in the teens to single digits at most locations.

Today:  A storm front is approaching the forecast area today, with increasing cloud cover and winds expected throughout the day. Snowfall is expected to begin in the late afternoon with only 1-3″ expected during the day. Overnight on Friday we expect 10-15″ of snowfall in Girdwood and Turnagain Pass and closer to 24″ in Portage and Placer. Temperatures will be on the rise as the storm approaches, increasing from the low teens F this morning to the mid to high 20s F by this evening. Wind speeds will start out in the 5-10 mph range this morning and gradually increase to 15-25 mph out of the south this afternoon. Overnight winds will average 50-60 mph with gusts of 75 mph+.

Tomorrow:  Another 10-12″ of snowfall is expected during the day on Saturday, with temperatures continuing to increase and rain line reaching up to 900-1100′. Strong winds will remain with averages of 25-35 mph and gusts of 50 mph+. Light snowfall is expected to continue on Sunday with temperatures decreasing snow line expected to return to sea level late Sunday evening.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 10 0 0 70
Summit Lake (1400′) 4 0 0 -*
Alyeska Mid (1700′) 15 0 0 67
Bear Valley – Portage (132′) 17 0 0
Grouse Ck – Seward (700′) 12 0 0 43

* Snow depth sensor not currently working at Summit Lake.

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 12 -* -* -*
Seattle Ridge (2400′) 10 -* -* -*

* Wind speed data is not reporting from Sunburst or Seattle Ridge.

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.