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Issued
Wed, February 16th, 2022 - 7:00AM
Expires
Thu, February 17th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE on all aspects and elevations due to a storm over the region this morning. Avalanches composed of the new snow (storm slabs, wind slabs and sluffs) will be likely to trigger by people and natural avalanches are possible. The danger is greatest in the mountains near Girdwood, Portage and Placer Valleys where up to a foot of new snow is expected. Less snow is expected at Turnagain Pass. Additionally, wet avalanches could occur later today in the lower elevations as rain on snow could be seen up to 1000′.

Cautious route-finding and conservative decision-making will be key if headed into the backcountry.

Special Announcements
  • AK DOT&PF:  There will be intermittent traffic delays today near mileposts 44 and milepost 37 on the Seward Highway (Summit Lake and the Wye Junction). Motorists should expect delays of up to 45 minutes between 10:00 am and 3:00 pm. Updates will be posted at 511.alaska.gov.
  • HEAVIER SNOWFALL is expected for Hatcher Pass and Chugach State Park, including Anchorage’s Front Range. Any area seeing heavy snowfall, rain on snow, and/or strong winds will have a rising avalanche danger.
  • Hatcher Pass Avalanche Center has issued an AVALANCHE WARNING. See hpavalanche.org for more information.
Wed, February 16th, 2022
Alpine
Above 2,500'
3 - Considerable
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

There were a few small skier triggered wind slabs yesterday on Sunburst (pictured below) and Tincan. These were in the 6-8″ deep range and around 30′ wide and composed of Monday night’s 3-6″ of snow.

Small skier triggered windslab off the Sunburst ridgeline, with light snow transport occurring. Photo Andy Moderow, 2.15.22.

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

Heavy snowfall began early this morning in most of Southcentral. Although this storm is favoring Hatcher Pass and the Anchorage area, our forecast zone should pick up anywhere from 6-15″. The higher snowfall amounts will be in Girdwood/Placer and Portage Valleys where 10-15″ is expected, between 6-10″ is expected for Turnagain Pass with a bit less further south in Summit Lake. Ridgetop winds have increased with the onset of the snow and should continue in the 20-30mph range with stronger gusts until this evening when the storm tapers off. All three weather factors are in play today, along with precipitation and wind, temperatures will be rising and rain could reach as high as 1,000′ by this afternoon, creating a rain on snow situation for those lower elevations.

With that said, we can expect all the storm snow avalanche problems out there. These will be storm slabs where over 8″ of snow falls, wind slabs, sluffs, and cornice falls. The size of avalanches will depend on the amount of new snow. In areas seeing a foot or more, expect avalanches to be big enough to be quite dangerous and may run further than expected. Today is a day to play close attention to new snow amounts and winds. This should be in conjunction with the usual red flags (recent avalanches, cracking in the snow and collapsing/whumpfing). If in doubt, sticking to areas that are outside of avalanche terrain will be a good way to have fun in the snow without worrying about triggering an avalanche or being in the way of a natural avalanche occurring above you.

Storm Slabs:  In areas with over 8″ of snow, and especially in places with a foot or more, expect to see slab avalanches in the storm snow. These could be on sheltered slopes as well slopes seeing a little wind effect. Adding to this problem will be today’s rising temperatures, which causes denser snow to fall over lighter snow (upside down storm).

Wind Slabs:  New wind slabs are being formed as we speak with the moderate to strong easterly ridgetop winds over the region. These could be anywhere from 8″ to 2′ deep or more depending on how much new falls. Wind slabs could also pull out older wind slabs from yesterday, making them a bit larger.

Sluffs (loose snow avalanches):  On steep slopes without wind effect, sluffs could occur naturally and will be easy to trigger. They could also trigger a larger storm slab further down the slope.

Wet Avalanches:  Unfortunately the rain/snow line could creep up to 1,000′ today. In this case, rain on snow has a good shot at causing wet loose avalanches in the lower elevations.

 

Snow total graphic courtesy of the National Weather Service, Anchorage Office. The snowfall numbers are slightly lower for Turnagain Pass due to some rain forecast to fall at 1,000. 

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

We are continuing to track the snowpack as a whole and the various layers of buried crusts that, in places, have weak snow associated with them. As we’ve been mentioning, shallow snowpack zones are the most concerning for an avalanche breaking in these deeper layers. These areas are on the far north and south of our forecast zone and extend into the interior Kenai. This includes the Summit Lake area (just to the south of our forecast zone).

Glide Avalanches:  A few reports of new glide cracks have filtered in. The photo below by Andrew from Tincan yesterday shows Seattle Ridge with a crack on the south end of the ‘Repeat Offender’ slide path, which is near the common up-track. Cracks have also been seen on Tincan’s south face.

Glide crack on Seattle Ridge, to the looker’s left of the common up-track. 2.15.22.

Weather
Wed, February 16th, 2022

Yesterday:  Mostly cloudy skies were over the region with a few snow flurries here and there. Ridgetop winds were generally south and westerly, but terrain forced flows into different directions. Seattle Ridge recorded light southeast winds while Sunburst saw moderate to strong west winds. Temperatures climbed to near 30F along ridgelines before falling again overnight.

Today:  Another storm has moved in early this morning and should peak just before noon. Snowfall totals in the high elevations will be 10-15″ in Girdwood/Portage/Placer valleys and 6-10″ in Turnagain Pass. The rain/snow line will be climbing through the day to 1000′ as temperatures rise with this event. Easterly ridgetop winds look to average 20-30mph with gusts to the 50’s.

Tomorrow:  A lull in weather is forecast tonight before another front pushes is tomorrow midday. This next system will bring cooler temperatures, strong easterly winds and around 4-10″ of additional snowfall. Stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 3 0.2 93
Summit Lake (1400′) 27 2 0.2 42
Alyeska Mid (1700′) 29 5 0.4 N/A

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28 W 14 44
Seattle Ridge (2400′) 27 SE 5 27
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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.