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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 26th, 2024 - 7:00AM
Expires
Wed, March 27th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. A variety of avalanche concerns exist as warm weather remains over the region. Fresh wind slab avalanches could be found and triggered above 2,000′ on steep slopes and gullies. Cornices are also a concern in the higher elevations along with a chance a larger slab could be triggered due to old buried weak layers 2 to 3 feet deep. Below 2,000′ wet snow avalanches could be triggered due to continued warm temperatures.

Roof Avalanches: Heads up – roofs are continuing to shed their snow with this warm weather.

Special Announcements

Hatcher Pass:  Check out HPAC’s Thursday forecast along with a fundraiser film at the BearTooth this Thursday. The Mountain in My Mind is the film, more details HERE!

Tue, March 26th, 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
Wed, March 27th, 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
Wed, March 27th, 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

No new avalanches were reported or seen yesterday. Continued cloud cover is hampering a good look onto the slopes. However, there’s a chance with all the winds in the high elevations and rain in the lower elevations, some type of avalanche activity is occurring out there. Especially in the Portage Valley zone where the heaviest precipitation is happening.

Portage Valley looking up the Byron Glacier drainage with Portage Lake on the far left. There is a popular summer trail called the Byron Glacier Trail that goes up this valley near an ice cave. The cave is formed from the creek running under avalanche debris that has accumulated for years and does not completely melt out during the summer. This area can be very dangerous due to avalanches releasing above sending debris into the drainage, especially during hot spring afternoons. Thanks to Dan Keeler for snapping this photo during a period of ‘lighter’ rain yesterday. 3.25.2024.

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

One more day of warm, a little wet, and windy weather. However today should be a bit lighter than the past two days in terms of winds as well as precipitation. There even could be a sliver of sun poke through this afternoon. Over the past 24-hours we’ve seen between 0.1″ of precipitation at Turnagain and 1.75″ in Portage Valley, Girdwood around 0.5″. Here are a few precipitation number from the past couple days:

48-hour precipitation numbers:
Girdwood Valley:  0.5 to 1.2″ of rain up to 1200′, 5-12″ of wet snow above 1500′
Portage Valley:  3″ or so of rain up to 1500′ and 30″ of snow in the Alpine
Turnagain Pass:  0.2 to 0.4″ of rain to 1200′, 2-4″ of snow above this
Summit lake:  Only around 0.1″ of rain to 1200′, an inch of wet snow above

Dry Snow Avalanches – Above 2,000′:  Ridgetop winds have slowed down since the past two days and are currently blowing from the east in the 10-15 mph range and gusting in the 20s mph. A variety of wind slabs have likely formed over the past few days and how big and sensitive they are will depend on location. There has been a couple of feet or more in Placer Valley and a foot or so in Girdwood but only a few inches at Turnagain. Hence the largest slabs will be in the Portage/Placer zones and the smaller ones at Turnagain Pass. As always, keep a close eye out for signs of wind loading, cracking in the snow around you, and any collapsing (whumpfing) in the snowpack. A group found cracking in wind slabs on Tincan yesterday.

Wet Snow Avalanches – Below 2,000′:  Light rain is expected to fall up to 1,000′ or a bit higher through today. At these lower elevations in general we can expect mostly wet snow with possibly some crusts on top where any kind of refreeze was able to happen. Below 1,500′ reports are the snowpack has lost most of its cohesion; meaning the surface and mid-pack crusts have melted and the whole snowpack is becoming one thick layer of wet saturated snow. At this point larger wet avalanches are prime to occur because the pack has essentially lost its strength. We have not seen these large wet avalanches yet, but we are looking for them. It’s good to remember both natural and human triggered wet avalanches are possible on steep slopes with wet snow. These can be more dangerous if they are on bigger slopes where they can gain momentum and entrain more wet snow as they move downhill.

 

Sunburst webcam yesterday at 4:30pm. Cloudy skies and low visibility! 

 

Sunburst webcam again at 3:00am this morning. A few snow flurries adding up to what looks to be an inch or so from overnight. 

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 are still concerned with a weak layer of facets and surface hoar that was buried just over two weeks ago. The layers seem to be found in most places at Turnagain Pass around 2 feet deep, but less so in other regions. How likely it is for a person to trigger a slab 2-3 feet deep is uncertain, but this would be a big avalanche and something to be wary of. Forecasters are getting into the field today, but there has been little traffic and new information for several days. If you do head onto the steeper slopes, be sure only one person is exposed at a time, have an escape route planned, and watch your partners from safe areas outside of avalanche runout zones.

Weather
Tue, March 26th, 2024

Yesterday:  Mostly cloudy skies were seen yesterday with heavier precipitation occurring in the evening and overnight. Between 0.25 and 0.5″ of rain was seen in Girdwood, a bit less at Turnagain, and almost 2″ in Portage Valley (the big winner). The rain/snow line was ~1200 to 1500′. Ridgetop winds were easterly in the teens with gusts near 30 mph. Temperatures hovered near 40 in the lower elevations and the mid 20sF along ridgelines.

Today:  Cloudy skies are expected again today as active warm weather systems keep moving through. Between 0.1 and 0.25″ of rain should fall to 1000 to 1200′ with 1 to 3″ of wet snow above this. Portage Valley and Seward again look to see closer to 0.5″ of rain and ~5″ of snow above 1,500′. Ridgetop winds look to bump up into the 20s mph with gusts in the 30s this morning from the east before backing off into the teens. Temperatures remain warm, near 40F in the lower elevations and the mid 20sF along ridgelines.

Tomorrow:  Wednesday is looking to be a start to a break weather. Skies are still expected to be cloudy, yet some sun could poke through. Ridgetop winds should be light and variable, temperatures look to cool slightly, and a chance for a few sprinkles here and there. Clearer skies are on tap for Thursday before more active weather moves in for the weekend.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 0 0.1 96
Summit Lake (1400′) 35 0 0 42
Alyeska Mid (1700′) 33 2 0.25 101
Bear Valley – Portage (132′) 39 rain 1.3
Grouse Ck (700′) 37 rain 0.2 64

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 ENE 13 39
Seattle Ridge (2400′) 28 SE 12 23
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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.