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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, April 5th, 2023 - 7:00AM
Expires
Thu, April 6th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE for two very different issues. First is springtime wet loose avalanches late in the day. Daytime warming and sunshine could melt surface crusts enough on solar aspects that wet loose avalanches may be easy to trigger and could release on their own. The second problem is the unlikely chance a person triggers a very large and dangerous avalanche that breaks in a weak layer buried around 3-6′. Careful terrain selection is recommended, which includes limiting exposure to steep terrain and runout zones.

Wed, April 5th, 2023
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 have been seen or triggered in the last several days in our forecast zone or close to it. Last Saturday, there was a large wind slab triggered by a snowmachiner in the Whittier area. The last known deep slab avalanche was remotely triggered from above by a skier just northeast of Girdwood. Before that slide, 18 very large human-triggered avalanches occurred that were between 3-6′ deep. All of these we suspect failed on faceted snow that was buried on March 14th. There has been relatively little traffic in the forecast zone the past week.

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

With a relatively warm night, a dusting of new snow, and the chance for sunshine and warm temperatures late in the afternoon and evening today, the surface crusts could melt enough to create a wet loose avalanche problem. Slopes facing the sun with rocks and vegetation, like the photo below, will be first to heat up. If you happen to be out during the ‘heat’ of the day, keep an eye on how wet and saturated the snow is becoming. If your boot/skis/board are sinking into gloppy wet snow, that’s when we don’t want to be on anything steep. These wet sluffs could be small and harmless, but can also entrain quite a bit of snow and become more dangerous.

 

Example of your classic springtime wet loose avalanche. This one is on the westerly aspect of Bird Ridge and occurred naturally last Sunday, April 2nd. Seen from the Seward Highway and photo taken by Paul Wunnicke on 4.3.23.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and 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

Someone triggering a very large deep slab avalanche is still a concern. It has been just over a week since the last one of these occurred. The problem ‘weak layer’ is old faceted snow that sits under all the March storm snow. This weak layer is roughly 3-6′ deep in the snowpack. Unfortunately, time can make this type of avalanche less likely, but the consequences if someone hits just the wrong spot can be deadly. This is the ‘scary MODERATE’ phase of Deep Persistent Slab avalanches. As we’ve been saying it’s a really tricky situation. Slopes can seem just fine, yet there is a small chance a slab can release that propagates across an entire bowl and runs through low angle terrain.

Yesterday we took at look at the SE face of Seattle Ridge where we have not seen any large slabs occur; specifically the Repeat Offender path above the motorized up-track. This was the first pit we have dug where we didn’t find an obvious weak layer. This is good news, yet we can’t hang our hat on one data point. All in all, this problem will finish the season with us and could cause large wet slabs when the snowpack really starts warming up. For the time being, this setup is still keeping us mostly traveling in the lower angle terrain with a conservative mindset.

If you are headed up ridges and into Alpine, lingering wind slabs may be found from the easterly winds on Monday and Tuesday. These are likely to be in the typical places where the east winds drift snow off ridgelines and in cross-loaded gullies. They are likely to be in the foot deep range. It’s also that time of year cornices can start becoming more unstable. As always give these a very wide berth.

 

Weather
Wed, April 5th, 2023

Yesterday:  Overcast skies with a few light snow flurries were over the region. A trace to an inch fell is most locations. Ridgetop winds were gusty from the east (10-15mph, gusting in the 20’s). Temperatures were near 20F along ridgelines and in the mid 30’sF in the lower elevations.

Today:  Skies should be partly cloudy with some valley fog and a chance for sunshine this afternoon. Ridgetop winds look to be quiet (~5mph) from the west through the day. Temperatures are in the 20’sF this morning and could climb to near 40F at the mid elevations and 30F along the ridges by this afternoon.

Tomorrow:  Mostly sunny skies look to prevail through Friday before the next system heads in for Saturday. Ridgetop winds are forecast to be breezy from the west (10-15mph). Temperatures look to stay fairly cool, near 20F along the ridgelines.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 trace 0 91
Summit Lake (1400′) 30 1 0.1 45
Alyeska Mid (1700′) 30 trace 0.1 84
Bear Valley – Portage (132′) 34 1 0.23

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 E 8 22
Seattle Ridge (2400′) 22 SE 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.