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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 18th, 2024 - 7:00AM
Expires
Fri, January 19th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1,000′ for the threat of glide avalanches and wind slab avalanches. These are two very different concerns but both are easy to look for. Limit any time under those dark brown glide cracks in case they spontaneously avalanche. Additionally, watch for slopes and cross-loaded gullies with wind deposited snow. Yesterday’s strong winds created new wind slabs and these could be easy for us to trigger.

SUMMIT LAKE/SEWARD:  The strong northeast winds along the ridgetops are forecast to remain today south of Turnagain Pass. This will continue wind slab formation and some slabs could release on their own.

Special Announcements

Tomorrow Night – Forecaster Chat at the Girdwood Brewing Co! Andrew Schauer will be discussing the different shades of MODERATE danger at the Girdwood Brewing Co. (6:30 to 8pm Jan 19). What does “spicy moderate” mean? More details HERE.

Thu, January 18th, 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
Fri, January 19th, 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
Fri, January 19th, 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
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

One new glide avalanche was reported yesterday morning on Penguin Ridge, seen from Girdwood (photo below). As far as wind slabs go, the strongest northerly winds hit just as the sun was setting before backing off early this morning, so there could have been some natural wind slab avalanches that have yet to be seen.

New glide avalanche on Penguin Ridge above Girdwood. This avalanche is not in a well traveled zone, but many others have been. Photo by Andrew Schauer, 1.17.24.

Avalanche Problem 1
  • 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

The glide avalanche issue has been bumped back up to Problem 1 due to it’s threat to many backcountry travelers. The wind slab avalanche issue is still present, but wind slabs are unlikely to release naturally today with the decrease in winds.

Glide Avalanches:  These large destructive avalanches continue to release in popular areas of Turnagain Pass, Girdwood Valley. and Summit Lake at random. This type of avalanche is not triggered by a person, it is the snowpack slowly ‘gliding’ down a slope, creating a gaping crack, then at some unknown time releasing into a scary avalanche. We don’t want to be in the wrong place at the wrong time. It’s critical to avoid being near or under glide cracks as much as possible. If you do travel under them, be sure to watch the slope, go one at a time, and move fast.

Glide cracks in Lynx Ck drainage. These are what to look for and avoid being under. Andrew Schauer 1.17.24.

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

The northerly outflow winds picked up yesterday evening region-wide. This event has been interesting as they shifted more out of the northeast. The strongest gust recorded was 82mph at Mile 43 of the AK Railroad (on the south end of Bench Peak above Grandview). The next strongest was at Arctic Valley, 67mph. In the Turnagain Pass and Girdwood zones the NE winds were closer to 10-20mph with gusts in the 40s. Today the winds should remain NE but calm down to 5-15mph with gusts in the 20s. All that said, we can expect to see significant wind affected snow in the high elevations and exposed mid elevations.

Wind Slab Avalanches:  With yesterday’s winds, fresh wind slabs must have formed. These are likely to be found in unusual places, possibly lower on slopes, and likely to be stiff. They could be on the stubborn side, allowing a person onto them before releasing or maybe still quite touchy. Some areas may see enough wind again today for continued active wind loading. Either way, along with negotiating the glide cracks, keep a lookout for the classic red flags of active wind loading, stiff snow over softer snow, and cracks that shoot our from you.

Winds transporting snow off peaks and ridges yesterday. Photo was taken in the Grandview area looking south. Aleph Johnston-Bloom 1.17.24.

 

Small wind slab in the mid elevations in Lynx Ck yesterday. Andrew Schauer 1.17.24.

Weather
Thu, January 18th, 2024

Yesterday:  Clear skies were over the region with some patchy valley fog. A northerly outflow wind event peaked in the afternoon with ridgetops seeing 20-25mph sustained north to northeast winds with gusts in the 40’s. Temperatures remain in the 20sF at most elevations with some valley bottoms 5-15F due to cold air pooling.

Today:  Another clear sky day is on tap with breezy northeast winds and cold valley bottom temperatures. Winds along the peaks should decrease through the day blowing 5-10mph with gusts in the 20’s. Areas near Seward and Summit Lake will see 10-15mph NE winds and gusts into the 30’s. Temperatures are in the 20’s at the mid and upper elevations but in the single digits at road level due to an inversion.

Tomorrow:  Similar conditions are expected for Friday into Saturday. Clear skies, light to moderate NE ridgetop winds, and cold temperatures in valley bottoms. The next shot of precip may come next week, yet this is too far out to know for sure. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 21 0 0 80
Summit Lake (1400′) 13 0 0 NA
Alyeska Mid (1700′) 17 0 0 80
Bear Valley – Portage (132′) 8 0 0 –
Grouse Ck – Seward (700′) 21 0 0 51

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 NE 14 40
Seattle Ridge (2400′) 22 N 7 17
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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