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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, February 3rd, 2024 - 7:00AM
Expires
Sun, February 4th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. Wind slab avalanches 1-2′ deep are possible for a person to trigger today. An incoming storm this afternoon will bring increasing easterly winds that could form fresh wind slabs and cause natural avalanches on steep wind loaded features at upper elevations. Glide avalanches continue to be a concern and we recommend avoiding traveling underneath glide cracks if possible. Below 1000′ the avalanche danger is LOW.

Special Announcements

TODAY – Anchorage (Glen Alps): Avalanche Rescue Skills Workshop. Come join the Anchorage Nordic Ski Patrol and CNFAC forecasters to hone your avalanche rescue skills!! Participants of all skill levels are welcome between 10:30am and 3:30pm. There will be multiple stations set up to practice different rescue skills, ranging from introductory skills to testing yourself against the clock to get ready for a professional avalanche course. Dress warm and bring your avalanche rescue stoke to help build a safer Alaska backcountry community!

SnowBall 2024:  Mark your calendars for Valentine’s Day, Feb 14 (7-11pm @ 49th St Brewing). Details and tickets HERE. 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 our friends at the Alaska Avalanche School.

Sat, February 3rd, 2024
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, February 4th, 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
Sun, February 4th, 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
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

A small wind slab was reportedly triggered in the Tincan Library yesterday, about 6-8″ deep. We also received a photo of some recent wind slabs that released naturally in the Girdwood valley from cross loading winds.

Natural wind slab avalanche in Girdwood Valley seen from top of Alyeska. Photo 2.2.24

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

The winds have mostly died down this morning but we expect that wind slabs 1-2′ deep are still possible for a person to trigger today. Typically wind slabs heal quickly, meaning they are are much less likely for a person to trigger after they have some time to adjust. However, since there is a widespread layer of weak sugary snow underneath the most recent batch of wind slabs from the past two days they might take longer than normal to bond with the underlying snow surfaces. To identify areas with possible wind slabs look for signs of wind transport on the snow surface texture, hollow feeling snow, and shooting cracks on small, steep test features.

This afternoon winds are expected to shift to the east and increase to averages of 10-20 mph and gusts to 35 mph. This change in wind direction and increase in wind speeds will likely cause active wind transport along upper elevations ridgelines and form a new generation of wind slabs. Natural avalanches will become possible in steep wind loaded terrain once the winds pick up. Light snowfall will accompany the increasing winds, but with only 1-2″ expected by this evening there won’t be enough new snow to impact the avalanche hazard today.

Lightly wind affected snow near treeline on Lipps; this area still had soft snow, but it was firm enough from wind transport to cause shooting cracks in some areas. Photo 2.1.24

At upper elevations the strong winds from earlier in the week have formed anti-tracks and firm wind blown surfaces. Photo 2.1.24

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

It has been a few days since we observed a new glide avalanche. Hopefully that means that activity is slowing down, but we thought the same thing last week and then two very large avalanches released right above the Seattle Ridge motorized uptrack. Due to the unpredictable and highly destructive nature of these avalanches it is important to continue to give glide cracks a wide berth. We recommend avoiding glide cracks entirely if you can or minimizing your exposure time if you need to travel underneath them.

Weather
Sat, February 3rd, 2024

Yesterday: Clear skies and very cold temperatures in the negative teens to single digits F throughout the region. Winds were out of the NW at 5-10 mph with gusts to 25 mph. No new snowfall.

Today: A storm system is approaching the region today, which will bring increasing temperatures, clouds, and light snowfall. Temperatures are expected to climb into the single digits or low teens F throughout the day. Cloud cover will increase as the storm system approaches, with snowfall expected to start around 2 pm. Only 1-2″ of snowfall is expected today, but overnight another 2-3″ of snowfall is expected. This morning winds should be light at 0-10 mph out of the west before switching to the east around 2 pm and increasing to averages of 10-20 mph with gusts up to 35 mph.

Tomorrow:  Light snowfall is expected to continue throughout the day on Sunday, bringing a total of 3-8″ of snow accumulation from Saturday afternoon through Sunday evening. Winds should remain out of the east at 15-25 mph with gusts to 40 mph for most of the day on Sunday, before switching back to west and dropping to averages of 0-10 mph on Sunday evening. Temperatures should continue to rise into the teens to low 20s F during the day on Sunday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) -7 0 0 78
Summit Lake (1400′) -14 0 0 n/a
Alyeska Mid (1700′) -6 0 0 82
Bear Valley – Portage (132′) -13 0 0 –
Grouse Ck – Seward (700′) -9 0 0 55

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -3 W 8 24
Seattle Ridge (2400′) -4 N 3 14
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.
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