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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, March 22nd, 2023 - 7:00AM
Expires
Thu, March 23rd, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche Warning
Issued: March 22, 2023 6:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger is rising to HIGH today at all elevations. A storm bringing heavy snowfall and strong winds will rapidly increase the avalanche danger. Large natural and human triggered avalanches will become very likely with today’s 12-18″ of snow forecast. In areas sheltered from the wind, avalanches will remain likely within the new storm snow. Travel in avalanche terrain is NOT recommend. This includes being aware of slopes overhead that could release naturally and run into valley bottoms.

*There is an Avalanche Warning and NWS Blizzard Warning in effect.

SUMMIT LAKE / SNUG HARBOR / LOST LAKE:  The Avalanche Warning covers these regions as well – very dangerous avalanche conditions are expected today.

Roof Avalanches will continue to be a hazard with rain and/or above freezing temperatures.

Special Announcements

AK DOT&PF:  There will be intermittent traffic delays today, March 22, on the Seward Highway for Avalanche Hazard Reduction Work near mileposts 44 and milepost 45 on the Seward Highway at Summit Lake. Motorists should expect delays of 45 minutes or longer between 10:00 am and 2:00 pm. The parking area at milepost 45 will be closed. Please stay clear of the area while avalanche crews are operating. More info on road closures at 511.alaska.gov.

Turnagain Pass Avalanche Awareness Day – Rescheduled for this Saturday.
Cross your fingers the weather and parking lot conditions allow for us to hold the 2023 Turnagain Pass Avalanche Awareness Day on Saturday March 25th! Check back Friday (Mar 24) after 5pm in case we need to cancel due to unsafe conditions and/or lack of parking.

Wed, March 22nd, 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. 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.
Recent Avalanches

There were no known avalanches yesterday and not many folks out in the backcountry. We did investigate the large avalanche that was skier triggered two days ago in Summit Lake (outside of the forecast area to the south of Turnagain Pass). That report will be updated later today, but a video can be seen here.

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

Another round of snow and wind has moved in overnight. This event comes with a Blizzard warning for the road system from Girdwood to Seward and an Avalanche Warning for the mountains. Similar to last weekend’s event, we can expect many natural avalanches to occur through the day as the storm is peaking from ~9am to 3pm. Up to 18″ of snow could fall by 6pm and more in favored areas like Portage and Placer Valleys. Ridgetop winds are easterly averaging in the 30’s and gusting near 70mph.

Just like last Saturday, it’s a day to hunker down as we strongly recommend staying out of avalanche terrain. If deciding to brave the roads and parking, be sure to avoid being on, or under, steep slopes (more than 30 degrees). Natural avalanches are likely to be of various sizes and types, but some could be large enough to run much further than we may expect. As we saw from last weekend, debris ran into the flat terrain.

With this storm the most common avalanches should be wind slabs releasing under ridgelines and in cross-loaded gullies (like the road side of Seattle Ridge). These are often triggered by parts of cornices that break off from above. We also could see storm slabs in mid elevation treed areas that are sheltered from winds. This means slabs composed of the new snow from today, which will be somewhere in the foot to 18″ range. Temperatures are warming slightly during the day, which will makes storm slabs more likely as heavier snow falls on lighter snow. All in all, mid-March is not disappointing for snow lovers, but could test our patience.

 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

If we think back to the evening of March 14th (3.14, pi day), that’s when the stormy weather started after a 2-week dry spell. Those old surfaces from early March were sun crusts on solar aspects and weak, faceted snow on shaded slopes. As of yesterday, there was roughly 3-6′ of settled storm snow from the past week on this old early March surface. That interface remains a cause for concern. It was the culprit layer is many large avalanches last Saturday. It was also the weak layer in the large Summit avalanche that was skier triggered on Monday, mentioned above. Today, another 12-18″ will be adding stress and if avalanches break on that old layer, slabs will be in the 4-7′ range and surely able to send debris into the flats below.

Additionally, on the southern edge of the forecast zone (Johnson Pass area) to Summit Lake (outside of the forecast zone), even larger avalanches may occur. Here, there are even older weak layers buried deeper in the pack. A lot of uncertainty exists for Johnson Pass area, but Summit Lake has already seen avalanche breaking in deeper layers. That said, for the next couple days we should let the mountains do their thing and not be in the way. Yet when skies clear, we’ll be wary of these layers.

Weather
Wed, March 22nd, 2023

Yesterday:  Mostly cloudy skies with some patches of blue were over the region. An early morning snow shower added 2-3″ of snow. Light snowfall began again after sunset as the next storm slowly moved in. Ridgetop winds remained easterly, 10-20mph, with gusts into the 40’s. Temperatures have been hovering near 20F along the ridges and near 32F in the lower elevations.

Today:  The next storm is just ramping up now and will peak midday before tapering off tonight. Between 12-18″ is expected with a rain/snow line that could reach 500′ by this afternoon. Ridgetop winds will remain easterly in the 30-40mph range with gusts near 70. Temperatures should warm slightly with the storm, mid 30’sF in the lower elevations and mid 20’F along the ridgelines.

Tomorrow:  Mostly cloudy skies, with some breaks possible, are forecast for tomorrow. A few snow flurries may be seen but no accumulation is expected. Winds look to be light from the west and temperatures should cool slightly.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 8 0.8 103
Summit Lake (1400′) 29 0 0 49
Alyeska Mid (1700′) 29 7 0.5 90
Bear Valley – Portage (132′) 34 N/A N/A

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 NE 22 69
Seattle Ridge (2400′) 24 SE 10 25
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.