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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, March 21st, 2024 - 7:00AM
Expires
Fri, March 22nd, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Avalanche danger is expected to rise to CONSIDERABLE by this afternoon and evening with daytime warming. Wet snow avalanches are likely to occur in the mid and lower elevations on steep slopes and will be possible on higher elevation steep sunny slopes. Cornices may become easier to trigger as well and could also break off naturally. On steep shaded slopes there is still a lingering chance someone could trigger a large dry snow slab 2 to 3 feet deep.

*Springtime avalanche conditions exist today and through the evening as temperatures should climb higher than we’ve seen this season.

Summer hiking trails:  Trails such as the Byron Glacier Trail and Crow Pass Trail can be hit from debris by avalanches releasing above. It’s that time of year to avoid any trail that goes under avalanche paths, especially during the heat of day when it’s nicest to get out.

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!

Thu, March 21st, 2024
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
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
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
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 was a large wet loose avalanche reported in Placer Valley yesterday around 3pm. Witnesses say the slide started small and gained mass and momentum as it descended. This is a typical springtime wet snow avalanche; occurring when the much of the snowpack becomes wet and saturated. It was in the lower elevations, ending at sea level, where temperatures are warmer than up at Turnagain Pass for example. Please let us know if you see these occur, it’s incredibly helpful!

Large wet loose avalanche in Placer Valley, on the west side of the valley (SE facing slope). Thanks to Matt Sturgess for the photo. 3.20.24.

 

A close up of the start zone. A small wet loose avalanche was able to entrain what looks to be a couple feet of wet sloppy snow and fan out. 3.20.24.

Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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 sunny day is expected before a few clouds start streaming in tomorrow, Friday. By late this afternoon/evening lower elevations and parking lots could see temperatures rise to 45F, maybe higher. Ridgetops could rise to near 35F. This is around 5 degrees warmer than yesterday. So not a huge change, but enough that more wet avalanches are expected and most likely in the mid and lower elevations. It’s that time of year when the snowpack is crusty and tied together in the morning, then when it melts, avalanche danger increases dramatically.

Wet Loose Avalanches:  Steep slopes seeing direct sunshine and warming, especially in the lower elevations such as Portage and Placer Valleys, are likely to see more large wet loose avalanches later today. The snowpack has started its transition to becoming wet and saturated at these lower elevations during the heat of the day. Once the surface crusts melt, keep an eye on how deep that wet snow extends. Yesterday it was only an inch at 3300′, not enough for wet avalanches. But at the lower elevations it extended 1-2 feet deep and hence that wet loose photoed above occurred. Timing your outing to avoid areas that could see wet avalanches is key.

Cornices:  Springtime warming can also cause cornices to ooze over and start breaking off. Being extra cautious along ridgelines is good call. They can trigger either nothing or a huge avalanche below, as the one on Byron Peak did a few days ago (photo below). Anyone with a cornice story is likely to agree that they really can break off further back than you think.

 

Very large cornices along Byron Peak in the Portage Valley area. One appears to have broken off and triggered a very large avalanche below. This likely occurred in the past few days. Seen and photographed yesterday, 3.20.24.

 

Slab avalanche that was triggered by warming a couple days ago, likely on Tuesday, March 19. This was on the roadside of Seattle Ridge just across from the motorized parking lot. Photo taken 3.20.24.

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 were able to get to a new area yesterday and test the snowpack; essentially looked for any signs of slab avalanche activity on the weak snow under last week’s storm snow. We found it. It was a layer of buried surface hoar around 2 feet deep. The storm snow has settled a lot and is quite dense these days. The good news is, the layer did not react in our tests. This tells us it’s slowly healing but we are still getting concerning pit results elsewhere. It has also been 7 days since it was producing a bunch of avalanches. It’s that time when the chances of triggering a large slab are more on the unlikely side, but it’s still worrisome in the big picture.

For folks looking for that soft snow on steep slopes, keep in mind there is a good chance a weak layer exists 2 feet below your feet/machine, yet the chance it’s reactive is what’s in question. Hence what appears to be a surprise avalanche could occur. Safe travel practices such as exposing one person at a time, having escape routes planned, posting up to watch in safe zones, and knowing how to use your rescue gear in case the slope does slide are all great ways to stack the odds in our favor. Snow can do unexpected things now and again.

 

Snow pit at 3300′ on a NE aspect on the west side of the Seattle Ck headwall. No results in the pit despite finding the thin gray line of buried surface hoar. 3.20.24.

 

Weather
Thu, March 21st, 2024

Yesterday:  Mostly clear and sunny skies were seen yesterday with some patchy valley fog. Ridgetop winds were light from the west and calm in drainages. Temperatures were near 30F along ridges and 40F at sea level.

Today:  Another mostly sunny day is on tap with lingering fog along Turnagain Arm and in some drainages. Ridgetop winds should turn a bit southeasterly this afternoon, blowing 5-10 with gusts of 15 ish along the higher ridges. Temperatures should rise from the 20sF to the mid 30sF along ridges and mid 40sF at sea level.

Tomorrow:  The high pressure over Southcentral shifts east and should allow some clouds in for late Friday and through the weekend. However, it’ tough to say if they will be thick enough to not let the sun through at times. A chance for a rain or snow flurry is possible but no measurable precipitation is expected. Ridgetop winds should remain southeast to east 5-10mph gusting 15-20 at times along the ridges.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 0 0 99
Summit Lake (1400′) 30 0 0 44
Alyeska Mid (1700′) 32 0 0 102
Bear Valley – Portage (132′) 31 0 0
Grouse Ck (700′) 33 0 0 70

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26 W 4 15
Seattle Ridge (2400′) 29 NW 2 8
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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.