Turnagain Pass RSS

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, November 18th, 2023 - 7:00AM
Expires
Sun, November 19th, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

Today’s avalanche danger is MODERATE above 1000′. Above 3000′, there’s a risk of triggering a large avalanche up to 3-4′ deep on a persistent weak layer near the ground. Additionally, smaller 1′ deep wind slabs could be human triggered or release naturally in exposed areas near ridgelines and convex terrain features. Below 1000′, the avalanche danger is LOW.

Summit Lake: Limited information is available about the snowpack in Summit Lake, but the same persistent weak layer likely exists at higher elevations. Exercise caution when approaching high elevation terrain. On the west side of the highway, be mindful of strong winds during NW outflow events.

Special Announcements

Hatcher Pass – Conditions are quite dangerous right now, check hpavalache.org for more information!

Chugach State Park – Persistent slabs at higher elevations and fresh wind slabs are the main concerns for the front range, similar too the rest of the region. Our weekly outlook for the Chugach State Park will start Dec 1.

Danger Rating Outlook – This season, we’re introducing an outlook for avalanche danger ratings to give you a forecast of conditions for the next day. This additional tool aims to help you assess the trend in avalanche danger and plan your outings more effectively.

Sat, November 18th, 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, November 19th, 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, November 19th, 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
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

No significant avalanche observations have been reported in the last few days. One notable avalanche was triggered last weekend at upper elevations on the skiers side of Turnagain Pass in Goldpan bowl.

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

Welcome to the first forecast of the 2023/2024 winter, all of us at CNFAC are excited to kick off the winter with a relatively deep snowpack! It’s still early season so we don’t have a ton of information from the forecast area yet, so please share your observations.

Today is going to be cold, with temps in the single digits and moderate to strong NW outflow winds. Our main concern is a weak layer of faceted snow near the ground above 3000-3500′ in elevation, which could cause large avalanches up to 3-4′ deep in higher alpine areas. Due to the persistent nature of this weak layer there’s a risk of triggering an avalanche remotely, which means it could release above, beside, or below you. Last weekend a group of skiers triggered two large avalanches simultaneously on this weak layer in Goldpan Bowl on the skiers side of Turnagain Pass. The simple way to avoid this issue is to stay below 3000-3500′. If you venture higher we recommend carefully assessing the snowpack near the ground and using conservative terrain selection.

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

Our secondary concern today is fresh wind slabs around 1′ deep on leeward slopes, likely forming near ridgelines and convex features. NW outflow winds mainly impact Seattle Ridge and areas along Turnagain Arm rather than the skiers’ side of Turnagain Pass. To identify wind-loaded areas, look for visual cues on the snow surface and ski or ride onto small test slopes to check for shooting cracks or small avalanches.

This week, our field observations noted a layer of buried surface hoar about 1′ deep in the snowpack. While non-reactive in tests, if a wind slab forms on top of this surface hoar, it could make avalanches easier to trigger and possible to release on lower-angle slopes

High resolution weather model showing areas that tend to get stronger winds with NW outflow (colder colors show low wind speed and hotter colors high wind speed).

Weather
Sat, November 18th, 2023

Yesterday: Temperatures dropped into the teens at lower elevations and single digits at upper elevations yesterday, with light winds averaging 5-10 mph and moderate gusts up to 30 mph. Cloud cover was mostly overcast and obscured. No new snow was recorded in Turnagain Pass or Girdwood but Portage recorded 0.1″ of SWE in the past 24 hours.

Today: Cold temperatures ranging from the single digits to negative single digits are expected today. Strong NW gap winds along Turnagain Arm will average 15-25 mph with gusts possible up to 40 mph. Seattle Ridge and the west side of Summit Lake tend to receive the most impact from this wind direction while the skiers side of Turnagian Pass often sees lighter winds. Cloud cover should be mostly clear with no new snowfall expected.

Tomorrow: Sunday should be very similar to Saturday, with cold temperatures and NW outflow winds being the dominant features of the weather. The next weather system that could produce new snowfall is expected to arrive Monday night which should bring warming temperatures next week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 15 0 0 34
Summit Lake (1400′) 14 0 0 25
Alyeska Mid (1700′)
Bear Valley – Portage (132′) 23 1 0.09

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 5 WNW 7 32
Seattle Ridge (2400′) 10 NW 6 20
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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.