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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 13th, 2022 - 7:00AM
Expires
Fri, January 14th, 2022 - 7:00AM
Forecaster
John Sykes
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 will rise to HIGH today above 1000′. A strong storm system is impacting the forecast area throughout the day with 12 to 24″ of new snowfall and strong winds. Natural avalanches 2-5′ deep are likely and human triggered avalanches are very likely. Very dangerous avalanches conditions exist and we recommend avoiding avalanche terrain and being aware of overhead hazards due to high potential for natural avalanche activity.

The avalanche danger is CONSIDERABLE below 1000′. Today’s precipitation will fall as rain in this elevation band which will make wet loose avalanches likely. Be aware of the potential for avalanches releasing at upper elevations and running to the valley bottoms.

SUMMIT LAKE: Snowfall will be lower here, with 6-8″ of new snow forecast, than elsewhere in the region but strong winds at upper elevations could build fresh and sensitive wind slabs.

SEWARD/LOST LAKE/SNUG HARBOR: 18-24″ of new snow is expected in these areas through Friday afternoon. Current weather models are showing sustained heavy precipitation through Friday with potential for more snowfall than the core forecast zone. The combination of heavy snowfall and winds will create dangerous avalanche conditions with natural avalanches likely.  Be aware of avalanches releasing naturally at upper elevations and running into lower elevation areas.

Special Announcements
  • The National Weather Service has issued a winter storm warning for Whittier, Seward, Girdwood, and Moose Pass for heavy snowfall, strong winds, and rain on icy roadways causing hazardous travel conditions.
Thu, January 13th, 2022
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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. Dangerous avalanche conditions. 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
  • 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.

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

Today is a proper storm day, with intense snowfall and strong winds through the daylight hours. As of early Thursday morning we have already received 6 to 12″ of new snow (0.5 to 1.0″ of SWE) and winds have picked up to the mid-thirties on Sunburst with gusts up to 70 mph. Snowfall intensity and wind speeds are forecast to peak around noon today, with an additional 12″ of snow accumulation and sustained strong winds. Natural avalanches 2-5′ deep are likely and human triggered avalanches are very likely. Due to the amount of new snow avalanches can be triggered in sheltered areas in addition to wind loaded areas. It is pretty simple today, avalanche conditions are very dangerous so avoid avalanche terrain and be aware of overhead hazards because natural avalanches are likely and could runout to valley bottoms.

The snow line should be between 400-800′ today with wet snow falling up to 1200′. The southern flow direction of this storm system is likely to drop more snow in Girdwood, Portage, and Placer than Turnagain Pass. Several weak layers exist in the upper snowpack which could produce large avalanches with the added new snow load. These include a layer of low density new snow that fell early in the storm on Sunday (see video here) and a layer of buried facets on top of the New Years crust. Both these layers have shown signs of instability in recent tests (see ob here). Regardless of the exact weak layer, the snowpack is likely to be overloaded today with the rapid addition of new snow and strong winds.

 

Storm total snowfall from Wednesday afternoon (1.12.22) to Friday afternoon (1.14.22). Graphic courtesy of NWS Anchorage 1.12.22

Example of existing weak layers in the upper snowpack. In this location there is potential for failure on either a weak layer within the storm snow from Sunday/Monday or on a deeper layer of buried facets above the New Years crust. Photo 1.12.22

Weather
Thu, January 13th, 2022

Yesterday: Light to moderate snow showers and clouds in and out throughout the day. Snow accumulations of 6-12″ (0.5 – 1.0″ SWE) as of this morning.  Winds were moderate in the mid teens to twenties with gusts into the mid thirties. Temperatures hovered just below freezing at 1800′ and in the twenties at ridgetops.

Today: Today should be a full on storm day, with heavy snowfall and strong winds peaking during daylight hours. Accumulations of around a foot of snow today with potential for higher amounts in Girdwood, Portage, and Placer. Winds will be out of the east in the 40 mph range with gusts ranging from 60-90 mph. Snow level should be 400-800 ft with wet snow up to 1200 ft.

Tomorrow: The storm will shift to a more southerly flow on Friday, which means some areas will see continued and potentially increased snowfall intensity and other areas will see minimal additional accumulation. Currently, weather models are showing minimal additional snowfall in Turnagain Pass on Friday. However, in Girdwood, Portage, and Placer snowfall looks to continue throughout the day on Friday. The snow line elevation could rise a bit during the day as temperatures increase slightly. Stay tuned for updates as the system develops.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 6* 0.6 75*
Summit Lake (1400′) 26 1 0.1 26
Alyeska Mid (1700′) 31 8 0.7 NA

* Estimates due to snow depth sensor errors

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 ENE 25 69
Seattle Ridge (2400′) 25 SE 16 35
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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.