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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, April 10th, 2023 - 7:00AM
Expires
Tue, April 11th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE at all elevations today. With heavy snowfall over the past 24 hours, it is likely a person will be able to trigger an avalanche 1-2′ deep today. The new snow has fallen on a variety of weak surfaces and is expected to be especially reactive. There is also a much smaller chance of triggering a much bigger avalanche failing on weak snow buried 3-6′ deep or deeper. Today’s dangerous avalanche conditions require cautious route finding, which means avoiding traveling on or below steep terrain.

Special Announcements

The National Weather Service has extended their Blizzard Warning until 10 AM today.

CHUGACH STATE PARK: Yesterday a hiker reported triggering an avalanche near Flat Top. The slab broke above the hiker, who was able to stay on their feet and was not carried by the avalanche. More info in this observation.

We’re looking for your input! We’ve made some changes to the forecast this year, and we are curious to hear how well it has worked. This is your chance to give us some feedback that will help us continue to improve our forecasts. These advisories are for you and we want to know how we can make them better. We’ve put together a quick survey that should take 5-10 minutes to complete. If you have a chance, please Click here for the survey. We really appreciate your feedback

Mon, April 10th, 2023
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

We were able to easily trigger fast-moving dry loose avalanches on Eddie’s yesterday (more info here). It is likely there were natural avalanches with heavy snowfall in the past 24 hours, but we haven’t confirmed this yet.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Winter tightened its grip yesterday, with 10-12″ new snow in Girdwood and Turnagain Pass, and 12-18″ or more in Portage and Placer. All of this new snow was very low-density, equaling only 0.5-0.7″ snow water equivalent (SWE) in Girdwood and Turnagain Pass, and closer to 1.7″ in Portage. The storm buried an older layer of low-density snow sitting on top of firm surfaces, which should make for very reactive conditions today. We can expect to see fast-moving storm slabs and dry loose avalanches as snowfall tapers off today. With this light fluffy snow, it will not take very much wind to start to see wind slabs form, especially at higher elevations. Avalanche conditions are going to be dangerous today, and it is likely a person will be able to trigger avalanches 1-2′ deep within this new snow.

This touchy storm snow will require a cautious mindset today. This means avoiding steep terrain and minimizing time spent in runout zones. Avalanches involving this low-density dry snow have a tendency to run fast and far, so be sure to pay attention to steep slopes overhead, as well as the terrain below your feet.

Full-blown winter storm conditions on Eddie’s yesterday! This photo was taken in the morning, and there was 8″ snow on the ground by the time we were headed back down at 4 p.m. 04.09.2023

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

In addition to the avalanche concerns related to the new snow mentioned above, we are still paying close attention to the weak layer of snow that was buried in the middle of March and is now 4-6′ deep or deeper on average. The load from this storm is not huge, but it is adding a little bit of stress to the snowpack. We’ve been watching this layer slowly gain strength over the past two weeks, but it is still a concern. We’re still treading lightly given the high consequences of triggering a massive avalanche on this layer. The only way to truly manage a deep slab problem like the one we are dealing with is by avoiding traveling on or below steep slopes. As time moves on this layer is starting to heal, but with all of the new snow from the past 24 hours now is not the time to start poking around.

You can click here to view the video below if it doesn’t load in your browser.

Weather
Mon, April 10th, 2023

Yesterday: We had a full-on winter experience yesterday, with 10-14” low density snow equaling just 0.6-0.7” snow water equivalent (SWE) in Girdwood and Turnagain Pass, and 18-24” snow (1.7” SWE) in Portage and Placer. High temperatures stayed in the single digits to upper teens F with lows in the single digits to low teens F. Winds were mostly out of the west at 5-10 mph with gusts of 10-20 mph and stronger winds along the Turnagain Arm.

Today: Light snow showers will linger today before clearing out tonight, but we are only expecting another 1-3” snow. High temperatures should be in the mid teens to low 20’s F, with lows tonight in the mid teens F. Winds will be light out of the west this morning, switching to the east mid-day.

Tomorrow: There should be a break in the stormy weather starting later today through tonight, but things are looking to pick up again by tomorrow afternoon. This will start with increasing winds out of the southeast at 15-30 mph, with more snow expected later in the day tomorrow into tomorrow night. For now it is looking like we should see 4-6” with this next round, with more wintery weather on the way later in the week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 15 13 0.8 102
Summit Lake (1400′) 13 5 0.4 48
Alyeska Mid (1700′) 12 10 0.6 90
Bear Valley – Portage (132′) 18 18 1.7

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 5 W 5 13
Seattle Ridge (2400′) 7 N 3 9
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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.