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Issued
Tue, April 18th, 2023 - 7:00AM
Expires
Wed, April 19th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE at all elevations for today and tomorrow. Wet loose avalanches, and even some small slabs, are possible in the warmth of the day on all aspects below 2,500′ and on sunlit slopes in the high terrain. Lingering wind slabs may also be triggered in steep shady terrain at the high elevations that still harbor dry snow. Remember to give cornices a wide berth along ridgelines.

PORTAGE VALLEY hikers/bikers/xc skiers: Be aware of avalanches that could occur overhead as the day heats up. This area can see large wet slides that can run close to commonly traveled areas.

*WEDNESDAY AVALANCHE OUTLOOK:  There will be no forecast issued tomorrow, Wednesday. The next forecast will be Thursday, April 20. Look for an increase in wet loose avalanches due to warmer daytime temperatures forecast for Wednesday afternoon. In general however, avalanche conditions should remain similar to those on Tuesday and in the MODERATE category.

Special Announcements

We’re looking for your input!  If you haven’t done so yet, please consider taking 5-10 minutes to fill out a quick survey about the avalanche forecast. Click here. Big thanks to everyone who has responded!

Avalanche Center End of Season Operations:  Beginning this week we will forecast 4 days/week (Tuesday, Thursday, Saturday, Sunday). The final forecast is scheduled for April 30th.

Tue, April 18th, 2023
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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

After many natural wet loose avalanches occurred on Saturday, only a few were reported over the past two days. The last dry snow avalanche that we know of was the slab triggered on the upper face of Captain’s Chair. Take a minute to read that report HERE.

Avalanche Problem 1
  • 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

As spring slowly moves back into Alaska, the snowpack is beginning its transition from a cold dry snowpack to a summer melt-freeze one. With chilly nights and warm days, the transition is slower than if we were to get rainy warm weather. During these spring transitions we often see large wet snow avalanches, but that is probably still a week or two away. Until then, a smaller variety of wet snow avalanches in the top foot or so of the snowpack is the main concern. This is why paying close attention to melting surface crusts and soggy snow late in the day is important. This includes considering your exit route as the prime time for wet loose slides are between 3 and 6pm.

Beginning with east facing slopes, then south, and last westerly aspects, small to medium sized wet loose, and even shallow wet slabs, can be triggered by us or could release naturally as the day progresses. This will be more pronounced tomorrow, Wednesday, as warmer temperatures are expected tomorrow afternoon/evening. Once the surface crusts melt enough that your boot sinks down 6″ or more into soft wet snow then these wet loose slides on the steeper slopes are possible and it’s time to head to a cooler aspect.

Wet loose avalanche on Seattle Ridge from over the weekend. A great example of snow heating up around dark features (rocks/vegetation) to the point small chunks of soggy snow roll down the slope and entrain enough additional wet snow that the next thing you know there is a wet loose avalanche. Photo taken on Monday, 4.17.23.

 

Lingering Wind Slabs:  For those seeking the dry snow in the higher elevations, lingering wind slabs or some kind of surprise dry slab avalanche could be found. Weather stations have not shown strong enough winds to move snow since early Sunday morning, so any dry slab should be fairly stubborn. That said ,in steep rocky terrain where slopes are unsupported from below, this is the ideal place to find one of these older slabs. The slab triggered last Saturday on Captain’s Chair was most likely an older wind slab.

Cornices Falls:  Cornices tend to slowly ooze over during the warm weather and can become more likely for us to accidentally cause one to break off. Give these an extra wide berth and limit time under them.

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

While the main avalanche concerns lie in the upper snowpack, there is still a suspect layer of rounding facets buried 3-6′ deep. This layer was responsible for many very large human triggered avalanches in the second half of March, but we have not seen any activity on it for three weeks. Although it would be very unlikely to trigger an avalanche this deep now, we are keeping in the back of our minds, especially as the snowpack slowly warms. Once the snowpack starts seeing significant warming, we are anticipating some big wet slabs in the future. 

Weather
Tue, April 18th, 2023

Yesterday:  Mostly clear skies were over the region yesterday. Ridgetop winds were light from the north and west. Daytime temperatures warmed into the mid 30’s in the mid elevations while the ridgelines staying in the 20’sF.

Today:  Clear skies this morning should give way to some high clouds through the afternoon. Ridgetop winds are expected to be light and variable today before turning easterly overnight, 5-10mph. Temperatures should warm again into the mid 30’s around treeline and stay in the 20’sF along the higher peaks.

Tomorrow:  Mostly clear skies continue through Wednesday and even into the weekend. Ridgetop winds should be generally light and variable. Temperatures could climb several degrees higher tomorrow, Wed, afternoon/evening with daytime warming.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 0 0 90
Summit Lake (1400′) 30 0 0 42
Alyeska Mid (1700′) 32 0 0 84
Bear Valley – Portage (132′) 35 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 W 5 9
Seattle Ridge (2400′) 23 NE 4 10
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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.