The avalanche danger remains HIGH at elevations above 1,000′. Triggering a very large and dangerous avalanche is likely on all aspects. Between 3-5+ feet of snow has fallen in the past 4 days on older weak snow and crusts. The storm is moving out today but ridgetop winds are continuing to blow. Natural avalanches are possible and people could trigger large slides that send debris into valley bottoms. Travel is NOT recommended on, or below, slopes over 30 degrees.
The danger is CONSIDERABLE below 1,000′ where some crusts have formed due to a rain/snow mix in the storm snow. This makes triggering an avalanche less likely, however, large avalanches occurring above could run into this zone.
Sun, March 19th, 2023
Alpine
Above 2,500'
4 - High
Treeline
1,000'-2,500'
4 - High
Below Treeline
Below 1,000'
3 - Considerable
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
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.
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
Due to the stormy weather, heavy snowfall and white-out conditions, we do not yet know the extent of the avalanche activity that has occurred. We could not even see the bottom of the avalanche paths on Seattle Ridge and if there was any fresh debris in them. Something we hope to get eyes on today.
Avalanche Problem 1
Storm Slabs
Aspect/Elevation
Certain
Very Likely
Likely
Possible
Unlikely
Likelihood
Historic (D4-5)
Very Large (D3)
Large (D2)
Small (D1)
Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
The mid-March madness is finally slowing down for a couple days. The storm system over the region yesterday is moving out this morning leaving us with some cloud cover, a few flurries of snow, and continued ridgetop winds. The winds today look to stay easterly and in the 20-30mph range with stronger gusts. This is strong enough to keep moving the new snow around. Speaking of new snow, yesterday was a wallop. From 10am until midnight the mountains around Turnagain, Girdwood and Placer saw up to 18″. Check out the snow totals below from yesterday as well as from the storm series that began on Wednesday, March 15th.
The main point is we need to be extra conservative in case it really is easy for us to trigger large and deadly avalanches. In short, there has been a lot of new snow (3-5+ feet) that has fallen on questionable surfaces. These surfaces are slick sun crusts on south, west, and east aspects and a mix of faceted snow and wind hardened snow on shady aspects. We essentially have zero information on what has been happening in the mountains over the past two days. What we do know is all the ingredients are there for a bad setup and that’s worth paying attention to. Despite having this high degree of uncertainty, too many signs are pointing to very dangerous conditions.
Adding to the equation today will be the ridgetop winds. If they do continue to blow and load slopes, natural wind slab avalanches may occur. Whether these would create a much larger slab that takes all the feet of new snow is a question, but I would say it’s definitely possible.
Storm totals from yesterday only:
Girdwood: 12-16″ snow, 1.5-1.8″ SWE (Snow Water Equivalent)
Portage/Placer: 20-24″ snow, 2.1″ SWE
Turnagain Pass: 16-20″ snow, 1.8″ SWE
Summit Lake: 10-12″ snow, 0.9″ SWE
Storm totals since Wednesday (amount of snow over the older sun crusts and faceted snow from the 2 week dry spell):
Girdwood: 35-46″ snow, 3.5-4″ SWE
Portage/Placer: 50-70″ snow, 5-6″ SWE
Turnagain Pass: 40-50″ snow, 4-5″ SWE
Summit Lake: 16-20″ snow, 1.8″ SWE
Travel Advice: Leave the steeper slopes alone and let the mountains settle out. Sticking to flat or shallow slopes with nothing steeper above us is a good plan. Basically, avoiding avalanche terrain, which includes runouts of avalanche paths that could be above us.
SUN EFFECT: Once the sun comes out and starts warming up this new snow, we can expect to see wet loose avalanches and even varying degrees of slab avalanches (small to big). If a slab composed of all the new snow pulls out, it will be very large. Remember, the hottest part of the day is 3-5pm.
A look at the new snow depth on the south end of Turnagain Pass where somewhat less snow fell compared to the northern end. Either way, A LOT of snow has fallen in the past 4 days. 3.18.23.
Avalanche Problem 2
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.
The 3-5+ feet of snow equates to roughly 3-5+ inches of water weight. This is a lot of weight for the snowpack in a short period of time. It may be enough to reactivate older buried weak layers that had gone dormant (become unreactive). The south end of the forecast zone from Pete’s North to Bench Pk is where this is most likely to occur. These are areas with a thinner overall snowpack. In the event an old weak layer wakes up, an extremely large avalanche may ensue that could put debris well into valley bottoms. Once skies clear we’ll get a better sense if this is an issue or not. Until then, we should keep this possibility in mind. One more reason to really be wary of very big avalanches now and in the days ahead.
Weather
Sun, March 19th, 2023
Yesterday: Heavy snowfall from 10am through midnight last night. New snow amounts during this time were in the 12-18″ range. The rain line crept up to 500′ or so at the end of the storm. Ridgetop winds were easterly averaging 20-30mph with gusts in the 60’s. Temperatures rose to the 20’sF along the peaks yesterday evening and into the upper 30’sF at sea level.
Today: The storm is exiting the region this morning. Partly cloudy to mostly cloudy skies with some snow flurries are expected through the day with 0-1″ of accumulation. Ridgetop winds are still elevated and should remain in the 20-30 mph range today with stronger gusts from the east. Temperatures have cooled into the 20’sF at most locations save for sea level where they are in the low 30’sF.
Tomorrow: Partly cloudy skies are forecast tomorrow, Monday. Ridgetop winds look to continue blowing 20-30mph from the east. Temperatures should remain cool, 20’sF at the mid and upper elevations. Another round of storms is expected beginning Tuesday. Stay tuned.
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.
Archives 
The Bottom Line
A look at the new snow depth on the south end of Turnagain Pass where somewhat less snow fell compared to the northern end. Either way, A LOT of snow has fallen in the past 4 days. 3.18.23.
