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Issued
Sun, April 23rd, 2023 - 7:00AM
Expires
Mon, April 24th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE at all elevations. A few inches of new snow and cooler temperatures should limit wet snow avalanches on slopes above 1,000. However, fresh small wind slabs could form on slick crusts in the higher elevations. Additionally, on steep north facing slopes with dry snow there remains the unlikely chance a person could trigger a large slab, 3 or more feet deep, as occurred last week.

PORTAGE VALLEY: Be aware of avalanches occurring overhead during warm afternoons. This area can see large wet slides that can run close to commonly traveled areas.

*MONDAY AVALANCHE OUTLOOK:  A MODERATE danger looks to continue. Clearing skies and slightly warmer afternoon temperatures may cause wet loose avalanches to again be easy to trigger. The next forecast will be Tuesday, April 25.

Special Announcements

End of Season Operations:  We will be issuing forecasts 4 days/week (Tuesday, Thursday, Saturday, Sunday) until April 30th. If conditions warrant, updates will be posted in early May.

Sun, April 23rd, 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

With the cooler temperatures yesterday, the afternoon sun was only able to trigger a few wet loose slides in steep southerly terrain. Otherwise, it was a fairly quiet day in the backcountry.

Wet loose avalanches from the past two evenings on a NW facing slope in the Lost Lake area. As the sun gets higher it’s harder and harder to find dry snow on northerlies. 4.22.23. 

Avalanche Problem 1
  • 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

An unseasonably cold weather system is pushing through today that brought chilly overnight temperatures and a few inches of snow this morning. As of 6am around 3-4″ of snow has fallen in Girdwood Valley, 4-6″ in Portage Valley, 2-4″ at Turnagain Pass, and what looks like just a trace in Summit Lake. Snow level is at sea level but could rise slightly this afternoon. Ridgetop winds are fairly light, around 5-10mph, but from all directions; above 3,500’ish they are NE while mid and lower elevations are more westerly.

All that said, with such small snow amounts the only new avalanche problem might be small wind slabs at the high elevations. These would be in the 4-8″ deep range depending on how much snow falls and should not pack much of a punch. The new snow is falling mostly on crusts and if an area sees over 4-5″ then shallow sluffs should be expected. This afternoon, small wet avalanches may again occur in the low elevations, below 1,000′, with daytime warming.

The main problem that could wreck our day is still the unlikely chance someone triggers another deep slab. Hence, why this remains ‘Problem 1’ despite a few inches of new snow. Once skies clear enough to access the higher terrain, we really want to be sure everyone seeking the last remnants of dry powder on shaded slopes understands there are lurking old weak layers. The Big League avalanche was a sore reminder that old weak layers just can never totally be trusted. Unfortunately there is no way to accurately assess this problem in the field. For those that don’t want to mess with it, avoiding big steep slopes and steep rocky terrain is the only option.

MONDAY:  If the sun comes out tomorrow any new snow that heats up will easily sluff off the frozen crusts that cover most of the surfaces on steeper slopes. Again, with only a few inches of new snow these should be fairly small sluffs.

General Springtime Hazards:  Other hazards associated with the spring melt cycle include cornice fall and glide avalanche release, which are both very unpredictable and can produce large avalanches. We recommend minimizing time spent underneath large cornices or glide cracks.

 

A few inches of snow to sea level this Sunday morning. This is the RWIS Portage Curve camera, 7am April 23rd. Gap winds are blowing along Turnagain Arm, but fairly quiet in the mountains.

Weather
Sun, April 23rd, 2023

Yesterday:  Partly cloudy skies were over the region with light north and westerly winds along the ridgelines (5-10mph). Temperates climbed to the 30-40’s but cooled into the 20’s overnight at all elevations.

Today:  A cool storm system is moving through. Cloudy skies and light snow showers should persist into the afternoon. Around an inch of additional snow is expected on top of the 2-5″ already seen early this morning. Ridgetop winds are variable in the 10mph range. Temperatures are expected to climb into the mid 30’s at the lower elevations but remain in the mid 20’sF in the Alpine.

Tomorrow:  Partly cloudy skies are expected tomorrow with light and variable winds. Daytime temperatures could warm into the 40’sF at sea level and near 30F at the higher elevations.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36 2 0.1 85
Summit Lake (1400′) 36 0 0 39
Alyeska Mid (1700′) 37
Bear Valley – Portage (132′) 41 3 0.4

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26 NW 6 14
Seattle Ridge (2400′) 28 NNW 4 13
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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.