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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, March 22nd, 2024 - 7:00AM
Expires
Sat, March 23rd, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations today. Fresh wind slabs 6-12″ deep that formed overnight are likely for human triggering at upper elevations along ridgelines. Triggering a larger avalanche on a buried weak layer 2-3′ deep remains possible, and is most likely in the afternoon when warm temperatures and sun weaken the snow surface. If the sun makes a surprise appearance today, wet snow avalanches on solar aspects are possible in the afternoon.

Special Announcements

THIS SATURDAY!!  Turnagain Pass Avalanche Awareness Day – March 23
Swing by the Turnagain motorized parking lot between noon and 4pm to grab a hotdog, practice your beacons skills, chat with the forecast team, and possibly test out a demo snowmachine provided by local dealers. We are crossing our fingers the sunny weather lasts a couple more days!

Arctic Valley SkiMo Race with Alaska Avalanche School – Sunday, March 24
Dust off your best costume and come join Alaska Avalanche School for their 9th annual SkiMo race fundraiser at Arctic Valley. This is a super fun and family friendly event that is available to racers of all skill levels, with long and short format race courses. Follow the link for more information!

Fri, March 22nd, 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, March 23rd, 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, March 23rd, 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

A few new wet avalanches were observed yesterday, including the first wet slabs of the season being observed in the Summit Pass area. There was also a new debris pile observed from a distance in the Crow Creek area near Goat Shoulder, but we have no information other than seeing the fresh debris.

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 pickup up overnight and were averaging 15-20 mph with gusts to 30 mph out of the east for about 9 hours. Despite the melt freeze crusts on the surface at lower elevations, it is likely that the winds found some snow to move around at the upper elevations and formed fresh wind slabs 6-12″ deep. These will be most likely for a person to trigger on high elevation northern aspects where there is most likely to be soft, dry snow available for the wind to transport. To identify areas harboring wind slabs keep an eye out for active wind loading, hollow feeling snow on the surface near ridgelines or gully features, and use small test slopes to check for shooting cracks or small avalanches.

Wet snow avalanches are less likely today because we are expecting cloudy conditions. However, forecasting cloud cover is very tricky and it is possible that the sun could have more impact than we are expecting. Keep an eye out for how much the sun is impacting the snow surface today especially on southern aspects. Depending on the cloud cover overnight the melt freeze crust on the surface may not have refrozen as deeply as yesterday, which means conditions could soften up earlier in the day and start to cause wet loose avalanches if the sun comes out. If you find that you are sinking in below ankle depth on slopes being melted by the sun it is time to move to a shadier aspect to avoid the potential for wet avalanches. The weakening crust will also make triggering a larger avalanche on a buried weak layer more likely (see problem 2).

Finally, cornices are in prime condition to start shedding off the ridgelines right now. Try to avoid spending time underneath cornices that are being heated up by the sun. They can fail randomly and have to potential to trigger avalanches on the slope below.

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

The buried persistent weak layers that caused a bunch of human triggered avalanches last week are still lingering in the snowpack and seem to still have the potential to cause large avalanches. There are two concerning weak layers buried about 2-3′ deep in the snopwack, one is buried surface hoar and the other is a layer of facets. We got unstable test results in our snowpits on Sunburst and Magnum on both these layers yesterday, which is a sign that they need more time to gain strength. Since these weak layers are within the upper 3′ of the snowpack it is possible for the weight of a person to trigger an avalanche on these weak layers, especially in the afternoon when the melt freeze crust on the surface has softened and taken away some of the strength of the surface snow.

The best way to manage this type of avalanche problem is to stick to lower angle terrain to avoid the potential to trigger a large avalanche. Digging snowpits and using stability tests like a compression test or an extended column test are good ways to identify and assess the weak layers, but we don’t recommend over relying on snowpit information in your decision-making (example of good use of snowpit info for decision-making) because it is common to get false stable or inconsistent stability test results.

Concerning snowpack structure at 2500′ on Sunburst with two persistent weak layers in the upper 3′ of the snowpack which could cause large avalanches. Photo 3.21.24

Weather
Fri, March 22nd, 2024

Yesterday: High overcast clouds in the morning followed by mostly sunny skies in the afternoon. Temperatures were in the mid 30s to low 40s F at low elevations and low 30 F at upper elevations. Winds were light during the day, averaging 5-10 mph out of the east with gusts to 15 mph. Around 6pm the winds picked up and were stronger over night, with averages of 15-20 mph and gusts to 30 mph out of the east.

Today: Cloud cover moved into the area overnight, and we are expecting a chance of rain and snow showers throughout the day. No significant snowfall accumulation is expected and rain line should top out around 900′ this afternoon. Winds are expected to remain in the 15-25 mph range out of the southeast with gusts up to 35 mph. Temperatures are expected to rise to the mid 30s F at low elevations and low 30s F at upper elevations this afternoon.

Tomorrow: Cloud cover is expected to stick with us tomorrow, with snowfall expected to start in the afternoon and only a trace to 1″ of accumulation by Saturday night. Winds will pick up again with the arrival of snowfall with averages of 20-30 mph out of the southeast starting around noon. Rain line is expected to remain around 1000′ on Saturday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 0 0 98
Summit Lake (1400′) 31 0 0 44
Alyeska Mid (1700′) 34 0 0 101
Bear Valley – Portage (132′) 35 0 0
Grouse Ck (700′) 35 0 0 70

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 29 E 10 31
Seattle Ridge (2400′) 29 ESE 6 16
Observations
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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.