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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, February 27th, 2023 - 7:00AM
Expires
Tue, February 28th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. The strong northwest outflow winds from the past two days have built sensitive wind slabs 1-2′ deep that will remain possible for a person to trigger today. We’ve seen loading on all aspects with this round of wind, so be sure to carefully assess steep slopes and avoid traveling in terrain with fresh wind slabs on the surface. The most dangerous terrain features will be found below ridgelines, convexities, and in steep gullies. The danger is LOW below 1000′.

*A storm system moving in tomorrow is expected to bring around a foot of new snow by Wednesday morning, along with strong winds. Expect increasing danger tomorrow and Wednesday, and be sure to stay tuned for updated information.

SUMMIT LAKE: In addition to the concerns with fresh wind slabs from the outflow event, there are multiple weak layers capable of producing large avalanches in the middle of the snowpack, and weak snow on the ground. Extra caution is advised in the Summit Lake area.

SNUG HARBOR / LOST LAKE / SEWARD: Strong winds will continue in these zones today, with natural avalanches possible and human-triggered avalanches likely on wind loaded slopes.

Special Announcements

The National Weather Service has issued a Winter Storm Watch for an approaching storm that should start impacting our area tomorrow morning, bringing strong winds and up to 10-18” snow by Wednesday.

Turnagain Pass Avalanche Awareness Day – 2023:  Mark your calendars for Saturday, March 18th, and swing by on your way to or from your backcountry ride or ski!! Test your beacon skills, chow down on hot dogs, and bring your questions. The Alaska Avalanche School will be there along with a chance to demo snowmachines from Alaska Mining and Diving Supply and Anchorage Yamaha and Polaris. More details HERE!

Mon, February 27th, 2023
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

There were no new avalanches reported yesterday within our advisory area. The last human-triggered avalanche was on Saturday on Magnum, where a snowboarder triggered a wind slab avalanche, was caught and carried and able to ride away. More details here.

Just outside of our advisory area on Mt. Eva in Seward, skiers triggered two small avalanches on what looks to be wind-loaded mid elevation terrain. Nobody was caught in either avalanche. More details in this observation.

The crown of a small skier-triggered avalanche near Seward yesterday. Photo: Hannah Smith. 02.26.2023

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

The northwest winds that have been blasting the area for the past two days will be dying down through today, but the damage has already been done. Wind slabs that have formed during this event will remain reactive today, making human-triggered avalanches possible in wind-loaded terrain. We saw active loading on every aspect yesterday (more details in our observation from Seattle Ridge). We need to be smart about accessing steep terrain today, being careful to avoid any steep slopes that were loaded by these recent winds. Most wind-loaded slopes will have a smooth appearance, compared to the rough textures from slopes that were previously scoured. The most likely places to run into trouble will be steep slopes just below ridgelines, convexities, or steep gullies. Slopes with old tracks still visible are less likely to have fresh wind slabs on the surface. Luckily, the terrain with the best skiing and riding will also be the safer terrain. This will be on slopes protected from recent winds, where there is still 4-6″ soft snow on top that hasn’t been blown around by the winds.

Dry Loose Avalanches (Sluffs): On steep slopes that have remain protected from the recent winds, it is likely a person will trigger dry loose avalanches within the soft snow on the surface. These are unlikely to become big enough to bury a person, but they can still be dangerous if they carry you through terrain traps like cliffs, rocks, or trees.

Winds have been at work moving snow around in the upper and mid elevations (as seen here by the snow blowing off the Seattle Headwall), but there is still plenty of sheltered terrain down low that hasn’t been touched. 02.26.2023

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

We know there are multiple layers of facets and buried surface hoar in the upper 2-3′ of the snowpack, but they are becoming more and more stubborn, making avalanches less likely. For now, it is unlikely that a person will trigger an avalanche on one of these layers, but it is not entirely out of the question. It is worth considering the outside chance of triggering a large avalanche on one of these layers, and traveling accordingly. This means avoiding high-consequence terrain that increases the severity of triggering an avalanche. It also important to stick to safe travel protocol– watching your partners from safe areas outside of runout zones, and only exposing one person at a time to steep terrain.

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

Weather
Mon, February 27th, 2023

Yesterday: Strong northwest winds were blowing all day. Around Turnagain Pass, average wind speeds were around 10-15 mph for most of the day, but winds in Summit and near Grandview were averaging 30-45 mph with gusts up to 85 mph overnight. Temperatures were in the single digits F at upper elevations and in the upper teens to low 20’s F at lower elevations, with overnight lows in the single digits to low teens F. Skies were sunny with a few clouds and no precipitation.

Today: Northwest winds are expected to die down today, with average speeds around 5-10 mph and gusts of 10-20 mph near Turnagain Pass and Girdwood. Winds will be much stronger down near Lost Lake and Seward. Temperatures will stay cold today, with highs in the single digits F and lows in the negative single digits. Skies should be sunny with a few clouds possible, and no precipitation expected.

Tomorrow: A low pressure system moves into the area tomorrow, bringing a major change in the weather. We are expecting to see 4-6” snow during the day tomorrow and another 4-6” overnight. It is looking like we should see snow down to sea level for this one. The storm will bring with it strong easterly winds, with sustained speeds around 20-30 mph and gusts of 35-50 mph. Temperatures are looking to climb back to the mid teens to low 20s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 13 0 0 65
Summit Lake (1400′) 6 0 0 37
Alyeska Mid (1700′) 13 0 0 69
Bear Valley – Portage (132′) 20 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 2 NW 9 28
Seattle Ridge (2400′) 8 NW 8 25
Observations
Recent Observations for Turnagain Pass
Date Region Location
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02/15/24 Turnagain Observation: Sunburst
02/13/24 Turnagain Observation: Tincan Backdoor, Center Ridge
02/12/24 Turnagain Avalanche: Tincan Trees
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02/10/24 Turnagain Observation: Tincan
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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.