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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, November 29th, 2023 - 7:00AM
Expires
Thu, November 30th, 2023 - 7:00AM
Forecaster
Andrew Schauer
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 quickly rise to HIGH as a strong storm hits today. Strong winds and a foot or more of new snow will make very dangerous avalanche conditions. It will be very likely a person could trigger an avalanche, and we are expecting to see some natural activity as the storm unfolds. This is the kind of day to avoid traveling on or below avalanche terrain.

 

CHUGACH STATE PARK: Unfortunately, the Front Range will see all of the strong winds with barely any of the snow today. This will make wind slab avalanches the main concern.

Special Announcements

The National Weather Service has issued a Winter Weather Advisory for strong winds and heavy snow for the Kenai Peninsula.

New weekend outlook products:  Starting this Friday, Dec. 1, we will begin issuing Weekend Avalanche Outlooks for Chugach State Park, the Summit Lake/Central Kenai zone, and the Seward/Southern Kenai zone. These Outlook products will be published Friday evenings and will provide avalanche information for these three new areas for us.

Wed, November 29th, 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
Thu, November 30th, 2023
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Thu, November 30th, 2023
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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. 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 reported avalanches were the wind slab avalanches we saw (and triggered) two days ago on Tincan (details here).

Debris just above treeline on Tincan’s CFR from natural avalanches during the last storm (Sunday). Similar activity is on the way today. 11.27.2023

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

A strong storm system will be impacting the area today, and it’s looking like Turnagain Pass is right in the crosshairs. Precipitiation intensity will ramp up through the day, with 6-10″ snow expected in Girdwood, Seward, and Summit, 12″ at Turnagain Pass, and around 2 feet in Portage and Placer. Heavy precipitation will be accompanied by strong easterly winds, with average speeds around 30-45 mph and gusts of 50-60 mph through today into tonight. The rain line will stay much lower for this storm than it has been lately, bouncing between 300 and 1200 feet.

That active weather will make the avalanche danger rise rapidly through the day.If this storm delivers as predicted, we will be hitting HIGH danger by this afternoon. With all of that snow and strong wind today, most steep slopes will be able to produce avalanches with human triggers, and we will most likely see natural avalanches later in the day. Elevations below 1000′ will see up to an inch of rain in the next 12 hours, making wet loose avalanches a big concern below treeline. The snow has just started falling as of 6:00 this morning, but conditions are going to deteriorate quickly. Long story short, all signs are pointing to very dangerous avalanche conditions and travel in avalanche terrain is not advised today.

Predicted 24-hour snow totals (top) and water totals (bottom). It is looking like this storm will favor coastal areas (as always), and also Turnagain Pass. Graphic courtesy of NWS Anchorage. 11.29.2023

Weather
Wed, November 29th, 2023

Yesterday: Skies were mostly cloudy, with wind ramping up from average speeds of around 10 mph in the morning to 45 mph overnight, and gusts as high as 75 mph early this morning. Precipitation also picked up overnight, and as of 5:00 a.m. stations are showing around 5-8” snow equaling 0.4-0.8” moisture in Girdwood and Turnagain Pass, with up to 1.8” of moisture closer to the coast in Portage and Seward. The rain line made it up to around 1000 feet, with high temperatures in the upper 20’s to upper 30’s F, and the coldest temperatures in the past 24 hours yesterday morning in the low 20’s to low 30’s F.

Today: We should see strong winds and heavy precipitation today. Storm intensity should peak this afternoon, with 6-10” snow likely in Girdwood, around 12” at Turnagain Pass, and closer to 2 feet in the higher elevations in the Portage and Placer valleys. The rain line will bounce between 300 and 1200 feet. Winds will remain strong out of the east, with sustained speeds of 30-45 mph and gusts of 50-60 mph. High temperatures will be in the mid 20’s to 30 F, with lows in the low to upper 20’s F.

Tomorrow: The storm will linger tomorrow, but it is looking like it will start backing off late tonight. Expect to see another 4-8” snow, with the rain line dropping to around 200 feet as the storm passes. Winds should back off slightly, but will remain strong with average speeds of 25-35 mph and gusts of 30-50 mph. High temperatures should be in the mid 20’s to low 30’s F, with lows in the low to mid 20’s F. Skies will remain cloudy, but the clouds might start to break up later in the afternoon.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 6 0.5 36
Summit Lake (1400′) 29 4 0.3 21
Alyeska Mid (1700′) 32 4 0.6 26
Bear Valley – Portage (132′) 38 0 1.76

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 27 76
Seattle Ridge (2400′) 26 SE 13 61
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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.