Turnagain Pass RSS

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, February 10th, 2024 - 7:00AM
Expires
Sun, February 11th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche Warning
Issued: February 9, 2024 9:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger remains HIGH above 1000′. The potential for very large human triggered avalanches still exists due to the heavy snowfall yesterday on top of buried weak layers 2-3′ deep. We recommend a very conservative approach to avalanche terrain today. Southerly winds could cause natural avalanches in wind exposed areas which could run out to lower elevations.

Below 1000′ the avalanche danger is CONSIDERABLE. This elevation band has a much weaker snowpack than typical. We are uncertain how the wet snow and rain that fell at low elevations yesterday is impacting the potential for human triggered avalanches. Carefully assess snowpack conditions before committing to steep terrain and be aware of runout zones.

Roof avalanches are likely as the temperatures increase and precipitation continues. Be aware of where you park, enter buildings, and where kids or dogs are wandering.

Special Announcements

SnowBall 2024:  Valentine’s Day, Feb 14 (7-11pm @ 49th St Brewing). The evening promises costumes, finger food, a rocking band, silent auction, and of course plenty of great company. Join us in supporting Chugach Avy as well as the Alaska Avalanche School. Details and tickets HERE.

Sat, February 10th, 2024
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Sun, February 11th, 2024
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, February 11th, 2024
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

We received some reports of small natural and human triggered storm and wind slab avalanches yesterday from folks travelling in treeline and below treeline elevations in Girdwood and Turnagain Pass. Visibility was definitely challenging and looks to remain that way today, so observations of larger natural avalanche activity will be hard to come by.

Small natural avalanche in the sheltered meadow seen through a gap in the trees on Tincan. Photo from Paul Wunnicke 2.9.24

Avalanche Problem 1
  • 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

It is the day after a big storm, which is the most likely time for human triggered avalanches. Weak layers that developed during the cold snap in January are now buried about 2-3′ deep and have the potential to cause very large avalanches. While we are not expecting any more significant snowfall today, the added load from new snow and wind yesterday have stressed these weak layers to the point where the weight of a skier or rider might be enough to trigger a large avalanche. We recommend a very cautious approach to avalanche terrain today. Persistent weak layers can cause avalanches on relatively low angle terrain and potentially connect multiple adjacent terrain features into a single avalanche. Remote triggering is also possible, which means you could trigger an avalanche from below, across, or above a steep slope.

Southerly winds averaging 20-30 mph with gusts to 45 mph are expected throughout the day, which could cause natural avalanches that have the potential to step down to these deeper weak layers. We recommend avoiding runout zones from overhead avalanche paths, especially in areas that are being actively wind loaded.

Snowpack structure in Crow Creek area of Girdwood prior to the storm on Friday. Photo 2.8.24

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

Yesterday’s storm lived up to the weather forecast, with over a foot of new snow across the forecast area combined with winds averaging 30-60 mph with gusts up to 96 mph from Thursday night through Friday night. Today it is still possible to trigger an avalanche 1-2′ deep in sheltered areas where the snowpack is still adjusting to the new snow load. Winds will shift to the south today, but are still expected to average 20-30 mph with gusts to 45 mph which is plenty strong enough to move all that new snow around into fresh wind slabs. Visibility might make it challenging to see where the active wind loading is happening today, so keep an eye out for shooting cracks or small avalanches on small test features to identify areas harboring wind slabs. Natural avalanches 1-2′ deep are likely in areas experiencing active wind transport.

Here are the storm totals (*estimated mid elevations*) from across the forecast area:

  • Turnagain Pass: 12-16″ (1.3″ SWE)
  • Girdwood: 15-19″ (1.7″ SWE)
  • Portage/Placer: 20-28″ (2.4″ SWE)
  • Summit Lake: 3-6″ (0.4″ SWE)
  • Seward / Lost Lake: 4-6″ (0.4″ SWE)

Proper storm day visibility from the Turnagain Pass RWIS camera yesterday. Photo 2.9.24

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

Don’t forget about those glide cracks that are hidden under the new snow! These things can avalanche at anytime, as you know if you’ve been reading along this month. Looking for crinkly snow surfaces can help to clue us into these things as well as looking for just the cracks. Any slope with an unnatural look to it is suspect to slide. The advice remains the same; do our best to avoid being under them and if needing to travel under them, go fast, one at at time, and watch the slope as well as out partners.

Weather
Sat, February 10th, 2024

Yesterday: Heavy snowfall and strong winds. Snow totals ranged from 4-12+” yesterday, with Girdwood and Portage receiving more snowfall on Friday compared to Turnagain Pass. Rain line crept up to 800-1000′ during the day. Winds averaged 45-65 mph out of the east at upper elevations throughout the daylight hours with gusts to 96 mph.  Temperatures were in the mid 20 F at upper elevations and low to mid 30s F at lower elevations.

Today: Unsettled weather will continue today, with cloudy skies expected to persist and snow showers bringing 0-2″ of additional snowfall. Rain line should drop back down to 200-300′. Winds are shifting to the south this morning and will remain elevated today with averages of 20-30 mph and gusts of 45 mph. Temperatures should remain in the low to mid 20s at upper elevations and high 20s to low 30s at lower elevations.

Tomorrow: Sunday may bring some periods of less cloudy sky cover, but snow showers are expected to continue off and on with little snow accumulation. Winds should remain out of the south but drop off to averages of 5-15 mph with gusts of 25 mph. Temperatures are expected to decrease overnight tonight into the high teens to low 20s F at upper elevations and mid to high 20s F at lower elevations. Another snow storm appears to be on the horizon starting Monday morning, stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 4 0.4 88
Summit Lake (1400′) 33 1 0.1 42
Alyeska Mid (1700′) 31 12 1.08 97
Bear Valley – Portage (132′) 37 rain/snow 1.5 –
Grouse Ck (700′) 34 2 0.3 60

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 35 96
Seattle Ridge (2400′) 25 SE 13 28
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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.
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