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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, March 1st, 2024 - 7:00AM
Expires
Sat, March 2nd, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. The NW winds over the past 3 days have formed wind slabs 1-2′ deep in exposed areas which will be possible for a person to trigger today. Loose snow avalanches will also be likely for a person to initiate on steep terrain. Below 1000′ the avalanche danger is LOW. 

SUMMIT PASS:  Continued moderate NW winds are forecast today. Wind slabs forming today or lingering from the past few days are possible for a person to trigger. A wind slab avalanche is this area could step down into a buried weak layer, creating a larger slide.

SEWARD/LOST LAKE:  Strong northwest outflow winds are expected to continue today. Natural wind slab avalanches are likely to occur as long as the winds persist.

Fri, March 1st, 2024
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
Sat, March 2nd, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
Sat, March 2nd, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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

No new avalanches were seen or reported yesterday.

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

Winds slabs are the name of the game today. With several days of NW outflow winds behind us and continued gusty NW winds expected in gap locations like Turnagain Arm today, human triggered avalanches 1-2′ deep in wind loaded areas are possible. For the most part these should be found at higher elevations where the winds have been stronger, but in some areas wind slabs can form at lower elevations near treeline. To identify areas with wind slabs keep an eye out for stiff or hollow feeling snow in wind exposed areas like near ridgelines, gullies, and convex rolls. You can also use small test slopes to check for shooting cracks and determine how reactive wind slabs are to the weight of a skier or rider.

Dry loose avalanches (aka sluffs) are expected on steep terrain. The cold temperatures the last few days have helped keep the surface snow light in areas sheltered from the wind, which tends to create prime conditions for sluffs. These avalanches are typically not large enough to bury a person, but they can knock you off balance in steep terrain. Best practice is to make a plan to manage your sluff before committing to steep terrain.

Cornices are also something to look out for today. At this point in the season cornices can be huge, and even on cold days direct sunshine can start to weaken their bond with the underlying terrain. Try to avoid spending time underneath large cornices and be aware that it can be easy to accidentally wonder too close to the edge of a corniced ridge.

We found a handful of small test slopes that were producing shooting cracks under the weight of a skier near treeline yesterday. Photo 2.29.24

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

The weak layer of facets that formed in January and are now buried 1.5-3′ deep are still in the back of our mind. Overall our field observations this week have shown that this layer is less concerning in Turnagain Pass compared to Summit Pass. However, we will continue to search for this layer and monitor the snowpack conditions. In areas on the southern end of the Turnagain forecast zone like Lynx Creek, Silvertip, and Johnson Pass it is more likely that an isolated pocket of unstable January facets could be lingering.

Weather
Fri, March 1st, 2024

Yesterday: Mostly sunny skies in the morning with overcast skies in the afternoon. Temperatures in the single digits F at low elevations and negative single digits F at upper elevations. Winds averaged 0-10 mph out of the NW with gusts up to 20 mph in Turnagain Pass. Stronger winds averaging 15 mph from the NW with gusts to 35 mph along Turnagain Arm. No new precipitation.

Today: The NW winds continue to be the main weather factor today, with averages of 5-10 mph and gusts up to 25 mph expected in Turnagain Pass. In gap wind locations like Turnagain Arm the NW winds are expected to average 10-20 mph with gusts up to 40 mph. The overcast skies that moved in yesterday are expected to give way to clear skies again by this afternoon. Temperatures should remain in the -10 to 10 F range. No new snowfall is expected.

Tomorrow: The pattern of strong NW winds is expected to diminish on Saturday, with NW winds decreasing to averages of 5-10 mph and gusts up to 30 mph in Turnagain Arm. Turnagain Pass should continue to have lower wind speeds with averages of 0-5 mph and gusts to 15 mph. Temperatures should remain in the positive to negative single digits F. Sunny skies and no new snowfall is expected on Saturday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6 0 0 89
Summit Lake (1400′) 7 0 0 46
Alyeska Mid (1700′) 7 0 0 91
Bear Valley – Portage (132′) 15 0 0
Grouse Ck (700′) 12 0 0 66

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -4 WNW 6 23
Seattle Ridge (2400′) 1 NW 3 11
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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.