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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, March 5th, 2023 - 7:00AM
Expires
Mon, March 6th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE on slopes above 1,000′. Triggering a lingering wind slab formed during the strong NW winds is possible. These are in the 1-2′ deep range and may be found off ridgelines, in cross-loaded gullies, and on rollovers. Additionally, solar warming this afternoon could affect the southerly aspects enough to make some small wet loose avalanches in steep rocky terrain. As always, give cornices a wide berth and watch your sluff on slopes with soft surface snow.

SUMMIT LAKE: Triggering a larger wind slab that is sitting on a weak snowpack is possible in the Summit Lake area. A natural avalanche was seen in this region yesterday as the area had stronger winds. Extra caution is warranted.

SNUG HARBOR / LOST LAKE: These southern zones were hit hardest by the winds over the past several days. Triggering wind slab avalanches is possible in this zone, similar to that of Turnagain Pass.

Special Announcements

Turnagain Pass Avalanche Awareness Day – 2023:  Mark your calendars for Saturday, March 18th, and swing by on your way to or from your backcountry ride or ski!! Test your beacon skills, chow down on hot dogs, and bring your questions. The Alaska Avalanche School will be there along with a chance to demo snowmachines from Alaska Mining and Diving Supply and Anchorage Yamaha and Polaris. More details HERE!

Sun, March 5th, 2023
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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 no new avalanches reported in the forecast zone yesterday. The last known avalanches were two and three days ago when several wind slabs released durning the strong NW outflow winds. To the south of the forecast area, at 6pm yesterday, a motorist saw an avalanche near Summit Lake at the Sterling Wye intersection with the Seward Highway. This was likely a natural wind slab as strong winds were impacting this area.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

After four days of strong NW outflow winds impacting the region, it appears the wind is finally on the decline. The one exception is along Turnagain Arm in Portage and Whittier where westerly gap winds are still being seen. These winds have affected a significant amount of snow regionally, yet lucky for Turnagain Pass there are still some areas that escaped the brunt. That all said, lingering wind slabs will be the main avalanche concern today. The next concern will be warming temperatures – an impressive inversion is in place this morning as high elevations have warmed into the mid 20’sF overnight while valley bottoms sit in the single digits. More on this in Problem 2 below.

Triggering a lingering wind slab is possible on the steeper slopes. Although we found wind slabs to be on the stubborn side yesterday, we can pretty much bet there are still some ready to pop in steep complex terrain. They may also become more reactive with daytime warming this afternoon. Slabs should be in the 1-2′ deep range and fairly easy to see by looking at the surface texture and smooth rounded pillows. Also, feeling for stiffer snow over softer snow and looking for cracks that shoot out from us are definitely clues we’ve found a wind slab. Look for them just off ridgelines, in cross-loaded gullies, and on the steep sides of rollovers.

Cornice Falls:  With easy travel along ridgelines, be sure to give cornices an extra wide berth. They can pull back further than expected, especially the larger ones. Also, the warming temperatures can make cornices a bit easier to break off if they are close to failure.

Loose Snow Avalanches:  Sluffs on steep slopes should be expected where loose snow exists on the surface. These looked to be on the smaller side yesterday, but areas with more loose snow, they could be large enough to possibly cause some grief.

A natural cornice fall from several days ago that we saw yesterday in the upper cirque of Spokane Creek (between Lipps and Pete’s N). The cornice looked to have pulled out a couple smaller wind slabs below. 3.4.23.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

Sunshine and warming temperatures. It’s that time of year where we need to remember about those afternoon solar effects. Not only is the sun expected to be strong today, there is also a ‘subsidence inversion‘ taking place that is warming the air mass in the upper elevations without the sun. Sunburst weather station has climbed to 26F overnight, believe it or not. Couple this with daytime warming and we could see some moist/wet loose avalanches this afternoon. This upper elevation warming is expected to continue into Tuesday when we could see overnight temperatures near 32F. Hence, wet loose avalanches, cornice falls, and even some weakening wind slabs or other funny business could begin to occur in the days ahead. Stay tuned and heads up!

 

 

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

There are a few questionable weak layers in the upper 2-3′ of the snowpack that may be capable of producing a surprise avalanche in isolated pockets. The most problematic terrain will be in areas with a thinner snowpack. This includes the Crow Ck area in Girdwood Valley, the southern end of Turnagain Pass (See this observation from Pete’s North on Wednesday) and down towards Summit Lake. Luckily, for most of our core advisory area it is looking like these layers are unreactive and unlikely to trigger. It has been several weeks since we’ve seen any avalanches failing deeper in the snowpack, yet it is worth keeping these layers in mind and adjusting your terrain use accordingly if you are traveling in a zone with a thinner snowpack.

Weather
Sun, March 5th, 2023

Yesterday:  Sunny skies were over the region yesterday. Ridgetop winds were generally NW in the 10-20mph range with gusts in 30’s. Temperatures were in the teens with some mid elevations reaching 20F with daytime warming.

Today:  Another sunny day is on tap today. Ridgetop winds should be light and northwesterly (5-10mph, gusting in the teens). Temperatures are inverted this morning with valley bottoms in the single digits while Sunburst has climbed overnight into the mid 20’sF!

Tomorrow:  The ridge of high pressure over Southcenteral looks to persist for several days. We can expect mostly sunny skies, light north to west winds and increasing temperatures. By Tuesday, we could see temperatures in the mid 30’sF at the high elevations as well as the lower. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 16 0 0 68
Summit Lake (1400′) 10 0 0 39
Alyeska Mid (1700′) 14 0 0 69
Bear Valley – Portage (132′) 11 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 12 W 10 22
Seattle Ridge (2400′) 10 N 6 20
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/13/24 Turnagain Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South
05/13/24 Turnagain Observation: Turnagain Pass non-motorized side
05/12/24 Turnagain Observation: Warm up Bowl
05/07/24 Turnagain Observation: Turnagain Pass Wet Slabs
04/29/24 Turnagain Avalanche: Turnagain aerial obs
04/27/24 Turnagain Observation: Johnson Pass
04/23/24 Turnagain Observation: Turnagain Sunny Side
04/21/24 Turnagain Observation: Bertha Creek
04/20/24 Turnagain Avalanche: Spokane Creek
04/16/24 Turnagain Observation: Cornbiscuit
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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.