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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 1st, 2024 - 7:00AM
Expires
Fri, February 2nd, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Avalanche danger is expected to rise to CONSIDERABLE in the upper elevations (above 2,500′) as strong NW outflow winds develop today. Wind slabs can form quickly on any slope seeing active wind loading. These slabs could be 1-2 feet deep and may release naturally or be easily triggered by a person.

In areas out of the wind, the danger remains MODERATE for soft slab avalanches on slopes with over a foot of new snow from last Monday (Girdwood, Portage, and Placer Valleys). Additionally, the threat of a destructive glide avalanche releasing at random still exists.

SUMMIT/SEWARD:  These zones could see stronger NW winds than Turnagain and rapidly forming wind slabs.

Special Announcements

CHUGACH STATE PARK:  Strong NW outflow winds look to hit Anchorage’s Front Range today as well. Watch for fresh wind slabs that could form quickly.

This Saturday – if temps are warm enough – Anchorage (Glen Alps): The Avalanche Rescue Skills Workshop was rescheduled for Feb 3rd. The event is hosted by the Anchorage Nordic Ski Patrol and Friends of Chugach Avy. Come anytime between 10:30am and 3:30pm to practice with your rescue gear. Several stations will be set up and folks available to assist and ask questions. Cross your fingers the weather isn’t too cold this time.

Thu, February 1st, 2024
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
Fri, February 2nd, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Fri, February 2nd, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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

No avalanches were seen or reported yesterday. The last avalanches were some human triggered slabs in the Girdwood area where up to 20″ of snow fell on Monday. They were 15-20″ deep and releasing at the new/old snow interface on Tuesday.

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

Skies may be sunny, but temperatures are cold, and winds are slated to pick up today. This morning the parking lots at Turnagain are -17F and Johnson Pass Trailhead and Summit Lake are sitting at -26F. Brrr! Adding to the cold, and the avalanche danger, will be an uptick in NW outflow winds. By 1 or 2pm ridgetops around 3,000′ and above should see NW winds in the 15-25 mph range with gusts in the 40s. This flow can sometimes split around portion of Turnagain Pass, sparing certain slopes, and sometimes produce southerly winds on the non-motorized side of the Pass. Either way for the forecast zone, this will be the main driver for avalanches issues.

New Wind Slabs:  If you are headed out today, sticking to sheltered areas will not only be good for limiting freezing skin, but avoiding freshly forming wind slabs. There is ample soft snow available for the winds to transport. Wind slabs can form quickly and if they do, should be easy to trigger. These are likely to be in the 1-2′ range on any slope that sees active wind loading. The good news is, because of the clear skies it should be easy to see where the wind is blowing and moving snow.

Persistent Slab Avalanches?:  In areas that saw over a foot of new snow last Monday, such as Girdwood and Placer Valleys, triggering a slab avalanche the depth of the new snow is still a concern. Monday’s snow fell on older weak faceted snow and surface hoar in some spots. Quick hand pits and jumping on small test slopes can be good ways to see if the new snow breaks off easily. Stepping onto big slopes with higher consequences could produce a large avalanche and careful snowpack assessment with a conservative mindset is recommended.

Snow surface conditions along Seattle Ridge yesterday, Jan 31. 

Avalanche Problem 2
  • 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

Those glide cracks are still looming on many slopes and still a bit hidden under Monday’s snow. A quick reminder that these cracks can avalanche at anytime. Along with looking for cracks, also look for wrinkly snow surfaces. This can help clue us into slopes harboring a potential glide avalanche. 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 we do travel under them, go fast, one at at time, and watch the slope as well as our partners.

 

Weather
Thu, February 1st, 2024

Yesterday: Sunny skies and cold temperatures (-20 to +5) were over the region yesterday. Ridgetop winds were generally light from the NW save for a few high ridgelines (~10 gusting 25mph) and gap winds in Seward and Whittier.

Today:  Another sunny and even colder day is on tap. Temperatures should stay between -25 and 0F. Ridgetop winds are looking to pick up from the NW (15-25 gusting 40-50 mph) as a moderate outflow wind event is expected.

Tomorrow:  Clear and cold conditions continue into Friday. The outflow NW winds should relax a bit but still are expected to be 5-15 mph with gusts in the 20s. Warming temperatures, clouds, and a few snow flurries should move in for the weekend.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) -10 0 0 80
Summit Lake (1400′) -17 0 0 n/a
Alyeska Mid (1700′) -5 0 0 84
Bear Valley – Portage (132′) -5 0 0
Grouse Ck – Seward (700′) -7 0 0 56

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -5 W 11 24
Seattle Ridge (2400′) -8 NNE 1 6
Observations
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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.