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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, March 20th, 2024 - 7:00AM
Expires
Thu, March 21st, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. By this afternoon, daytime warming may be enough to melt surface crusts and cause natural wet loose avalanches on steep southerly slopes. On shaded slopes, and sunlit slopes in the afternoon, there is still a chance someone could trigger a large slab 2 to 3 feet deep.

*Tomorrow, Thursday, warmer temperatures and sunshine is expected. This could bump the danger back to CONSIDERABLE for wet avalanches in the afternoon/evening hours.

Special Announcements

THIS SATURDAY!!  Turnagain Pass Avalanche Awareness Day – March 23
Swing by the Turnagain motorized parking lot between noon and 4pm to grab a hotdog, practice your beacons skills, chat with the forecast team, and possibly test out a demo snowmachine provided by local dealers. We are crossing our fingers the sunny weather lasts a few more days!

Wed, March 20th, 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
Thu, March 21st, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Thu, March 21st, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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 new avalanches were reported yesterday. However, it’s likely that at least some wet loose slides occurred in steep rocky terrain during the afternoon hot temperatures. Two days ago there was a report of a natural slab avalanche seen in motion from Tincan, this was on Monday and pictured below.

Avalanche seen in motion on Monday while digging a snowpit on Tincan. Thanks to Bryce Barnes for snapping this pic and the added info! 3.18.24.

Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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 springtime transition is beginning. Yesterday was the first ‘official’ day of spring and for the next 6 months our days will be longer than our friends in the lower-48. With increasing daylight and generally warming temperatures the snowpack will undergo a change from cold wintertime snow to warm/melt-freeze summertime snow. This transition can take weeks and create very large natural avalanches at times. Something to keep in mind for the next month or more.

Wet Loose Avalanches:  For today, despite the sunshine, a light westerly breeze may keep the snow a bit cooler than yesterday. However, surface crusts should melt to some degree by this afternoon. These crusts are found on southerly aspects and all aspects at the mid and lower elevations. A reminder that the warmest part of the day is between 2 and 5pm. Once these crusts melt then wet loose avalanches will become possible. Watch for indicator slopes like steep rocky terrain baking in the sun where the darker colors of rocks/vegetation enhances warming. This is often where wet loose slides start. Triggering a wet loose avalanche can be easy and inconsequential, but if caught very hard to escape from. These wet ‘sluffs’ can also trigger slab avalanches below.

Glide Avalanches:  Glide cracks are starting to open again. Pictured below is an opening crack on Eddies southerly face around 2,000′. If you see these cracks it’s best to avoid being under them, or go fast and one at a time, in case they happen to release into an avalanche.

Glide crack opening on Eddies south face. Seen from Tincan. Thank you to N. Dumont B. Matthys for the photo. 3.19.24.

Avalanche Problem 2
  • 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

There is a layer of weak snow and/or buried surface hoar between 2-3′ deep. It’s the layer under all that storm snow from last week. Snow pit tests are still showing concerning results, meaning the potential for us to trigger a large avalanche. Side note: for a reminder on the snow science jargon used in observations, check out Andrew’s Cheat Sheet on interpreting stability tests. The last avalanches we know of for certain were from last Thursday, but a few others, including the one seen on Monday on Seattle Ridge, may have released on this layer.

The most likely place to trigger a slab is where the surface still has soft settled powder (shaded steep slopes) or in the afternoon on southerly aspects when the surface crusts have melted. Essentially where the riding/skiing is best. The chances of triggering a slab 2-3′ deep is decreasing, but it’s still a possibility, which is that tricky situation we often find ourselves in.

It is difficult to assess buried weak layers because no obvious signs of instability may be present and the snowpack can ‘feel stable’. In this case, snow pits are the only tool that might provide useful information. Yet pit tests can provide false stable or inconsistent results and we don’t recommend relying entirely on pit information to make ‘go’ or ‘no-go’ decisions. If you decide to travel in steeper terrain we recommend giving yourself a wider margin for error, carefully evaluating the snowpack, and using safe travel practices to minimize your group’s exposure.

Snowpit at 2,700′ on a WSW aspect on Tincan from two days ago, Monday. Test results in an Extended Column Test showed a layer of buried surface hoar propagated across the column, a concerning test result. Photo and pit by Bryce Barnes 3.18.24.

Weather
Wed, March 20th, 2024

Yesterday:  High clouds were over the region with sunshine poking through regularly. Daytime warming bumped temperatures to low 30sF along ridgelines and 40sF at the lower elevations. Ridgetop winds were light and variable.

Today:  Another mostly sunny day is forecast today with some patchy valley fog. Ridgetop winds look to be light from the west around 5-10mph. Daytime warming should be similar to yesterday, rising from the 20sF at most locations to the low 40s at low elevations and low 30s on the ridges.

Tomorrow:  Two more mostly sunny days are shaping up for Thursday into Friday. High clouds with some patchy fog is still possible. Ridgetop winds should be light and variable. Daytime warming looks to be increasing for Thursday (a few degrees warming than today), and less so on Friday (similar to today).

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 0 0 100
Summit Lake (1400′) 28 0 0 44
Alyeska Mid (1700′) 32 0 0 102
Bear Valley – Portage (132′) 31 0 0
Grouse Ck (700′) 34 0 0 70

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28 ENE 3 10
Seattle Ridge (2400′) 31 SW 1 4
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.