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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, April 5th, 2024 - 7:00AM
Expires
Sat, April 6th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations today. Wind slabs 6-12″ thick are likely at upper elevations due to moderate winds from the west. Larger avalanches releasing on an icy crust buried about 1-2′ deep are also possible and have the potential to be triggered remotely. We recommend using small test slopes to check how reactive wind slabs are and evaluating how well the new snow from last weekend is bonding to the icy crust before committing to avalanche terrain.

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Fri, April 5th, 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
Sat, April 6th, 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
Sat, April 6th, 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

We did not get any reports of new avalanche activity yesterday. However, poor visibility for most of the day made it tough to spot avalanches.

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

An unsettled weather pattern persists over the forecast area today, with snow showers potentially bringing another 1-2″ of snow and moderate west winds averaging 15-25 mph. Wind slab avalanches up to 1′ deep forming at upper elevations along ridgelines, gully features, or convex rolls are the most likely avalanche problem to encounter today. To identify areas harboring wind slabs look for active wind transport along ridgelines, hollow feeling snow, and shooting cracks or small avalanches on test slopes. Areas with more snow and wind such as Portage Valley could see larger wind slabs.

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

In parts of the forecast area that received a foot or more of new snow last weekend it is still possible to trigger a larger avalanche 1-2′ deep at the interface of last weekends storm snow and a firm icy crust beneath. Wendy was able to investigate several human triggered avalanches in the Seattle Ridge area that occurred earlier this week and was alarmed at how large they are and the severe consequences of being caught in an avalanche like this.

There is a small layer of facets and buried surface hoar above the ice crust, which makes this avalanche problem more likely to be a concern for longer and contributes to the potential for remote triggering (triggering an avalanche on adjacent steep terrain from a lower angle slope). We recommend digging down to this layer to check how thick the new snow is and how well it is bonding to the icy crust before committing to avalanche terrain. To avoid this problem entirely you can always stick to low angle terrain.

Weather
Fri, April 5th, 2024

Yesterday: Overcast skies and light to moderate snowfall, totaling 2-4″ of new snow over the past 24 hours. Temperatures were in the low to mid 30s F at low elevations and low 20s F at upper elevations. Winds were moderate averaging 10 mph out of the east with gusts up to 35 mph.

Today: Snow showers are expected to continue today, but only add another 1-2″ of new snow throughout the day with rain line expected to remain at sea level. Skies should remain mostly cloudy to overcast and temperatures are expected to be similar to yesterday, with highs in the low to mid 30s F at lower elevations and low to mid 20s F at upper elevations. Winds will be the most notable weather characteristic today, with averages of 15-25 mph out of the west and gusts up to roughly 40 mph.

Tomorrow: Sporadic snow showers are expected to continue on Saturday, possibly adding another 1-2″ of new snow by the end of the day. Winds should shift back to the east and decrease to averages of 0-10 mph  during the day before ramping up again in the evening to averages of 15-25 mph out of the south east overnight. Mostly cloudy skies should persist and rain line is expected to stay at sea level or 100-200′. Temperatures look to stay constant, with daytime highs in the low to mid 30s F at lower elevations and low to mid 20s F at upper elevations.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 2 0.2 100
Summit Lake (1400′) 30 1 0.1 47
Alyeska Mid (1700′) 30 3 0.3 114
Bear Valley – Portage (132′) 35 0 0.3
Grouse Ck (700′) 34 2 0.2 77

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 E 10 32
Seattle Ridge (2400′) 23 ESE 7 17
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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.