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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, January 3rd, 2023 - 7:00AM
Expires
Wed, January 4th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′. Strong winds following three days of precipitation will make for dangerous avalanche conditions. Human-triggered avalanches up to 2′ deep within new and windblown snow are likely, with natural avalanches possible. There is a chance that an avalanche triggered near the surface may step down to deeper weak layers, making a very large avalanche.

The danger is MODERATE below 1000′. The biggest concerns will be loose wet avalanches and the chance for bigger avalanches triggered at higher elevations reaching lower elevation runout zones, especially in areas like the Portage Valley, which has seen heavier precipitation in the past 24 hours.

Special Announcements

Join us at the Girdwood Brewing Co. from 5:30-7:00 p.m. on Thursday, Jan. 19 for the second Forecaster Chat of the season. CNFAIC forecaster Andrew Schauer will open the night with an overview of the state of the snowpack, followed by a discussion on how safe terrain management changes depending on the type of avalanche problem at hand. More details here.

Tue, January 3rd, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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

The last known activity was during or immediately after the most intense period of precipitation two days ago.

Avalanche Problem 1
  • Storm Slabs
    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.

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

Over the past three days, the mountains near Girdwood and Turnagain Pass have gotten 2-3″ precipitation, falling entirely as rain below 1000′ and equaling roughly 2-3′ snow at upper elevations. For the more coastal areas near Portage and Placer, strom totals are now pushing  6-7″ water for that same time frame. The strong easterly winds that have been blowing since Saturday night are expected to back off slightly today, but with average speeds around 20-30 mph and gusts of 40-50 mph, there will still be significant wind loading through the day. The next system is fast approaching, and we should see precipitation and strong winds picking up again late this afternoon through tonight. All of this active weather means we are still dealing with dangerous avalanche conditions.

The biggest concern for today is the strong chance of a person triggering a large avalanche within the snow that has fallen since New Year’s. Yesterday on Tincan we found the new/old interface to be very reactive, especially on wind-loaded slopes (details here). With strong winds continuing today, conditions will remain reactive. The most dangerous conditions will be found at upper elevations near ridgelines, convexities, and steep gullies, but with all of the new snow over the past few days, we should be treating all steep terrain with skepticism. In addition to the new snow concerns, there is also the potential for very large avalanches failing on deeper weak layers- more on this in problem 2 below.

Click here to view the video below if it doesn’t load in your browser.

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

In addition to the new snow concerns mentioned above, there are two layers buried deeper in the snowpack that are worth keeping in mind. The weak snow that formed during the mid-December dry spell and was buried on Christmas is still being tested by continued loading. The deeper Thanksgiving layer is becoming less likely as it gains strength and gets buried deeper, but still cannot be ruled out. The good news with both of these layers is that they are gaining strength with time. For now, we need to consider the possibility of triggering a very large avalanche on either layer and dial back terrain accordingly. Given the unstable conditions with the new and windblown snow mentioned in problem 1, this is just one more reason why we’ll be avoiding traveling on and below steep terrain for now.

Those mid-December facets and the Thanksgiving layer are still giving us cause for concern, especially with the heavy loading event we’ve seen over the past three days. 01.02.2023

Weather
Tue, January 3rd, 2023

Yesterday: Steady precipitation continued yesterday, with weather stations at Alyeska picking up 0.5-1″ water, 2.4″ water at Portage, and 0.2″ water at Turnagain Pass. This precipitation fell as rain up to around 1300′, with snow at higher elevations. Winds were strong out of the east at 20-40 mph with gusts around 55 mph. Skies were cloudy with high temperatures in the upper 20’s to mid 30’s F, and low temperatures in the upper 20’s to low 30’s F as of 6:00 this morning.

Today: We are looking at a relatively quiet day of weather for most of the day compared to what we’ve seen over the past few days. Light precipitation may bring a trace to an inch of new snow under mostly cloudy skies, with rain lines staying close to sea level. Winds should back off slightly, but are still looking to average around 20-30 mph out of the east with gusts of 35-40 mph. Temperatures are also cooling slightly, with high temperatures in the upper 20’s to low 30’s F and lows dropping into the upper teens to upper 20’s F. Things pick up again this evening, with heavy precipitation and strong winds overnight.

Tomorrow: We may see another 6-12″ snow overnight tonight as a fast-moving system passes through from the southeast. The rain level is expected to bump back up to around 1000′ with this next round. It is looking like the winds will pick up with the precipitation, with average speeds as high as 40-50 mph out of the east and gusts reaching 60-70 mph. Things should calm down by tomorrow morning, with some breaks in the clouds possible for the first part of the day and winds backing off down closer to 20 mph. High temperatures should stay in the mid 20’s to 30 F, with lows in the mid to upper 20’s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 2 0.2 58
Summit Lake (1400′) 28 0 0 30
Alyeska Mid (1700′) 32 3 0.56 45
Bear Valley – Portage (132′) 39 0 2.4 –

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE 25 55
Seattle Ridge (2400′) 28 N/A* N/A* N/A*

*Seattle Ridge anemometer is rimed up and not reporting.

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.
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