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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, January 1st, 2023 - 7:00AM
Expires
Mon, January 2nd, 2023 - 7:00AM
Forecaster
Wendy Wagner
High Avalanche Danger
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger is HIGH at all elevations due to a warm, wet, and windy storm impacting the area. Heavy snowfall, rain, and strong winds are creating dangerous avalanche conditions. Large natural avalanches are likely occurring now and forecast to continue through the day. Human triggered avalanches are very likely. Travel in and below avalanche terrain is NOT recommended.

* Roof Avalanches:  Rain at sea level will make roof avalanches likely through today. Be sure to keep an eye on children and pets, and be careful where you park your vehicles.

Special Announcements

South of Anchorage:  The National Weather Service has issued a High Wind Warning and a Winter Weather Advisory south of Anchorage from Girdwood through Seward.

Anchorage area:  A different Winter Weather Advisory has been issued for Anchorage and other areas in Southcentral Alaska.

Sun, January 1st, 2023
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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.
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

2023 is crashing in with heavy rain, snow, and wind – Happy New Year!

A strong storm system is over the Eastern Turnagain Arm and already there has been around 1″ of rain at sea level and 10-14″ of snow in the higher elevations. The storm will peak today and taper off tomorrow. Today’s precip could bring 1-2″ of additional rain and up to 2 feet of snow to favored areas above 2,000′ (check out the graphic below). Turnagain Pass itself has seen 14″ of snow as of 6am with up to 18 more inches forecast today. The rain/snow line was around 500′ last night but expected to rise to 1,500′ by this afternoon and into tomorrow. Ridgetop winds are easterly and strong; hourly averages have been 30-40mph with gusts in the 70’s and should remain strong through the day.

Natural Avalanche Cycle:  Avalanches are likely occurring now in the mid and upper elevations due to the strong wind and heavy snowfall. It’s a textbook case of strong storms = avalanches. With 2-3 feet of new snow and wind in the Alpine, avalanches composed of just the new snow could be 2-4′ deep. These are the typical storm slab and wind slab avalanche types. As the rain/snow line rises and temperatures warm, this only adds to the instability by heavier snow/rain falling on lighter snow. Wet or moist snow storm slab avalanches could start releasing in the mid elevations with this ‘upside down‘ setup. Rain on snow at the lower elevations may or may not be creating wet snow avalanches as the prior snowpack was mainly crusts from the rain that occurred during the Christmas Storm. However, debris from avalanches above could run to the bottom of paths into the lower terrain.

If you are planning on braving the roads and getting outside today, be aware that travel in avalanche terrain is NOT recommended. This is the kind of day for sleeping in, and letting the mountains do their thing.

 

As of 6am 10-14″ of snow has already fallen above 1,500′. Another 12 to even 24″ of snow could fall today above 2,000′. Graphic courtesy of NWS Anchorage.

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

This storm is the second large loading event for the snowpack. It will again test those buried weak layers that sit around the Thanksgiving crust, or even any weak layer that may be left from the Christmas Storm a week ago. Again, we will do our best at seeing if any storm snow avalanches are able to break into buried weak layers. This will be an indicator of how those layers are healing and if they will continue to be a problem in our future or not. For now however, this deeper problem is just one more reason why avoiding avalanche terrain is a good call.

Weather
Sun, January 1st, 2023

Yesterday:  The New Year’s storm began yesterday with light rain at sea level and snow above ~500′. An estimated 8-14″ of snow has fallen so far above 1,000′, most of which occurred overnight. Ridgetop winds picked up into the 30-40mph range with gusts in the 70’s from an easterly direction. Temperatures are in the mid 30’s F at sea level and in the mid 20’s in the Alpine.

Today:  The brunt of the storm will be today bringing an additional 10-16″ of snow at elevations above 2,000′. The rain snow line looks to rise as high as 1,500′ by midday (plus or minus). Ridgetop winds are easterly blowing 30-40mph with gusts that could reach 80-100mph. Temperatures will slowly rise through the day to near 40F at sea level and 30F near ridgelines.

Tomorrow:  Lighter precipitation is forecast for Monday as the storm tapers. Around 3-5″ of snow should trickle in with the rain/snow line remaining fairly high (around 1,500′). Ridgetop winds look to still be strong (20-30mph averages) from the E to SE. Weather models are showing active weather through the week with another stronger pulse Tuesday into Wednesday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 14 (est.) 1.4 52 (est.)
Summit Lake (1400′) 31 3 0.3 29
Alyeska Mid (1700′) 31 6 0.5 40
Bear Valley – Portage (132′) 36 rain 1.6

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 NE 36 72
Seattle Ridge (2400′) 26 SE 12* 25*

*Seattle Ridge anemometer became rimed over around midnight last night, no data since 11pm Dec 31.

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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.