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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, April 1st, 2024 - 7:00AM
Expires
Tue, April 2nd, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger will remain CONSIDERABLE above 1000′. Another round of stormy weather is impacting the area this morning, making human-triggered avalanches 1-2′ deep or deeper likely, especially on wind-loaded slopes. Some areas may see intense snowfall today, and the most dangerous avalanche conditions will be in the places that pick up the most snow. This round of snow is falling on top 1-2 feet of snow that fell over the weekend, produced multiple avalanches yesterday and may not have settled out yet. All of this means avalanches may involve more than just the new snow that falls today.

SEWARD/LOST LAKE: This southern zone received a foot of snow Saturday night and may see storm totals approaching another foot by the end of today. This has fallen on a firm crust and is not bonding well. Very dangerous conditions will develop if this storm delivers, and travel in avalanche terrain is not recommended.

Special Announcements

The National Weather Service has issued a Winter Weather Advisory for Whittier, Seward, Moose Pass, and Turnagain Pass for heavy snowfall through 4 pm today.

Motorized Area Closure for Skookum Valley:  Per the National Forest Plan the Skookum Valley is closed to motorized use beginning today, April 1. Placer Valley remains open along with all other areas on the Forest.

Avalanche Forecast Survey: Simon Fraser University is collaborating with US avalanche centers to better understand how useful avalanche forecast information is for trip planning. This research will help drive development of future avalanche forecast products. Click here if you are interested in participating in a 20 minute survey.

Mon, April 1st, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Tue, April 2nd, 2024
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
Tue, April 2nd, 2024
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

We saw natural and human-triggered avalanches failing at the new/old snow interface from Girdwood to Seward yesterday. These were 1-2′ deep on average and include two remotely-triggered avalanches on Notch Mtn. in Girdwood, three skier-triggered avalanches on Tincan at Turnagain Pass, and a large natural avalanche on Tiehacker in Seward.

Three skier-triggered avalanches on Tincan, seen from the road yesterday around 5:30 pm. 03.31.2024

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

Active weather is expected to continue this morning before things start to clear out later in the afternoon, and it is likely we will see another 3 to 6″ snow in Girdwood and Turnagain Pass, with a foot or more possible near Seward and Lost Lake. This storm will likely involve some narrow bands of intense precipitation that could deliver much higher snow totals in isolated areas, which will mean some portions of the advisory area will likely see more dangerous avalanche conditions than others today. These convective storms are a challenge to predict exactly where the most intense precipitation will fall, so if you’re out in the mountains today you will have to be paying close attention to changing conditions and increasing danger if the storm intensifies.

We have less uncertainty in the winds, which have been at work moving snow into sensitive slabs all weekend and are still blowing this morning. Yesterday there were at least five human-triggered avalanches that were failing mostly on wind-loaded terrain features, around 1-2 feet deep. This next round of snow and wind is arriving while that older storm interface is still healing, and there is a good chance that an avalanche triggered today may involve more than just the snow that has fallen since last night.

Expect to find dangerous conditions in the backcountry today – especially in areas receiving the most snow – and travel accordingly. Steep wind loaded slopes will be the most likely terrain to produce avalanches, but in areas with a foot or more of new snow on the ground we may be able to trigger storm slab avalanches even on wind-sheltered slopes. Travel cautiously near avalanche terrain, and avoid steep slopes where the storm snow is starting to pile up, or where you suspect there is a stiffer wind slab on the surface.

Natural avalanche on Tiehacker in Seward. Similar conditions exist from Girdwood to Seward, and similar avalanches will be possible today. 03.31.2024

Weather
Mon, April 1st, 2024

Yesterday: Cloudy skies began to clear in the afternoon, with partly sunny skies later in the day. Winds were out of the southwest at 10-15 mph for most of the day, switching back to the east and increasing to 20-35 mph with gusts up to 55 mph overnight. High temperatures were in the low 20s F at ridgetops and low to mid 30s F at lower elevations, with lows in the upper teens to low 30s F. Precipitation has started again early this morning and weather stations in Girdwood and Turnagain Pass are showing 0.1-0.4” snow water equivalent (SWE) equaling 2-4” snow, with 6-8” snow closer to Seward and Lost Lake.

Today: Snowfall is expected to continue until this afternoon, with 3-5” snow expected for Girdwood and Portage, 1-3” for Turnagain Pass, and 4-6” for Seward. Cooler temperatures should keep the snow line near sea level. Winds are strong this morning, averaging 25-35 mph near ridgetops, but should taper through the day. Skies are expected to be partly to mostly cloudy with high temperatures in the mid 20s to 30 F and lows in the mid teens to 20 F.

Tomorrow: This round of stormy weather should pass later today, giving way to clearing skies and light northwesterly winds at 5-15 mph tomorrow. No precipitation is expected, and high temperatures should be in the upper teens to mid 20s F with lows in the low to mid teens F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 2 0.2 98
Summit Lake (1400′) 32 2 0.2 46
Alyeska Mid (1700′) 29 3 0.17 112
Bear Valley – Portage (132′) 36 tr. 0.44
Grouse Ck (700′) 35 10 0.6 76

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 SW-NE 18 54
Seattle Ridge (2400′) 22 SE 7 22
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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.