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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 6th, 2024 - 7:00AM
Expires
Sun, April 7th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. Watch for lingering wind slabs from yesterday’s northwesterly winds as well as new small wind slabs that could form later today as east winds increase. These are likely to be shallow in the 6 to 10 inch range. Triggering a larger slab composed of last week’s storm snow is becoming less likely but not out of the question. Additionally, keep an eye out for wet loose avalanches in case daytime warming is enough to melt surface snow/crusts.

PORTAGE VALLEY:  Up to 5″ of snow could fall in the mid and upper elevations today in areas close to the Sound.

Special Announcements

Hatcher Pass:  Check out the Saturday morning forecast from HPAC.

Chugach State Park:  A few inches of new snow fell yesterday along Anchorage’s Front Range, maybe more? Weekend Avy Report Here.

Sat, April 6th, 2024
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
Sun, April 7th, 2024
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
Sun, April 7th, 2024
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. 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 known avalanches yesterday. The last avalanche activity was from Tuesday April 2nd when several storm slabs were triggered after the April Fools’ Day storm.

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

The northwest outflow wind event yesterday ended up being fairly mild. Ridgetop weather stations reported gusts in the teens and 20s mph but really it was the lower elevations and gaps that saw the most wind – Turnagain Arm, Portage, and Seward. Winds have turned easterly overnight and will be on a slow rise today, peaking late tonight in the 15-20mph range and gusting in the 30s. That said, varying degrees of small wind slabs could be encountered in the mid and upper elevations.

There is not a whole lot of soft snow to blow around due to surface crusts that exist up to 2,000′ (ish) and on solar aspects in the higher terrain. Even north aspects have been reported to have some degree of surface crusts. If you are getting out today, chances are you’ll be tracking where the soft snow is for the best riding or skiing conditions. This is also where the winds may have formed a wind slab or two. Even though spring is here, it’s still fairly wintery in upper elevations. As always, watch for the classic wind slab clues: shooting cracks and smooth rounded pillows of snow.

Wet Loose Sluffs:  With the long days this time of year, even these cloudy days have time to warm enough to melt surface crusts by the afternoon. It’s that time of year to always be on the lookout for wet snow on slopes steep enough to slide. In this case wet avalanches become possible as the snow loses its cohesion.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

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

It’s been 4 days since a rash of avalanches were triggered on the first day after the April Fools’ storm. These slabs were all 1 to 3 feet deep and sliding on a slick crusty bed surface. Since then we have not heard or seen any more avalanches like this; there have not been many folks out either. We’ve been able to dig in various places in the snow enough to feel like this type of avalanche is becoming much less likely to trigger. Reasons being: the setup was probably due in large part to the storm slab being so fresh (less than 24 hours after the storm),was in areas where a slick crust sits under the storm snow (mid elevations W and S), and the slab above has turned from soft snow to crusty snow. If someone was to find the perfect combination and trigger a slab it would most likely be on a steep mid elevation slope at a time when the surface crusts are soft. Sticking to our good travel protocols (exposing one person at a time and watching our partners) are always good in case a surprise avalanche occurs.

Looking ahead to warmer days when the top foot of snow gets really soft and soggy, we could start seeing slabs sliding on these buried crusts. This is not likely the case for a while but something we’ll be keeping an eye out for.

The sun has been trying to poke through for several days now, and will keep trying for the weekend. Image from the Sunburst webcam at 4pm yesterday, 4.5,2024.

Weather
Sat, April 6th, 2024

Yesterday:  Mostly cloudy skies were over the region yesterday. Ridgetop winds were generally light from the northwest except through the gaps where strong winds were seen along Turnagain Arm, Whittier, and Seward for instance. A few snow flurries fell but no measurable precipitation was recorded. Anchorage’s Front Range on the other hand saw several inches of new snow due to the moist northwesterly flow.

Today:  Mostly cloudy skies are expected again today. Ridgetop winds have swung easterly overnight and should steadily increase through the day and by tonight blow 10-15mph with gusts in the 20s after sunset. Light precipitation is expected in Portage Valley and near the coast with up to 5″ of new snow above 500′, yet it looks like only a trace for Turnagain Pass. Temperatures should climb to near 40F by the afternoon at sea level and remain in the 20s F along ridgelines.

Tomorrow:  Another day with mostly cloudy skies, but a better chance for some sun to shine through, is expected for Sunday. No precipitation is forecast. Ridgetop winds should remain  from the east (10mph gusting in the teens). Temperatures again look to be near 40F at sea level and in the mid 20s F along ridgelines.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27 0 0 98
Summit Lake (1400′) 28 0 0 46
Alyeska Mid (1700′) 27 0 0 114
Bear Valley – Portage (132′) 34 0 0
Grouse Ck (700′) 33 o 0.2 73

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 NW 4 15
Seattle Ridge (2400′) 22 NNW 2 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.