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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, April 9th, 2024 - 7:00AM
Expires
Wed, April 10th, 2024 - 7:00AM
Forecaster
Mik Dalpes
Avalanche risk The Bottom Line

The avalanche danger will rise to CONSIDERABLE today above 1,000′ as a cold storm system moves through bringing strong easterly wind and heavy snow showers to sea level across our advisory areas. Natural wind slab avalanches will be possible and human triggered avalanches up to 1′ deep will be likely. MODERATE danger exists below treeline where heavy snowfall could make avalanches in fresh snow possible for a human to trigger.

PORTAGE VALLEY is forecast to see the highest snowfall amounts making this area more likely to have sensitive avalanche conditions.

The National Weather Service has issued a Special Weather Statement for heavy snow showers today in Girdwood, Portage, Whittier, Seward and Moose Pass.

Special Announcements

Avalanche Center End of Season Operations: This is the final week of daily 7am avalanche forecasts. Beginning April 15, we will forecast on Tuesday, Thursday, Saturday, and Sunday mornings. For the non-forecast days, we will give an avalanche outlook on the day prior. The final forecast for the season will be April 28.

How Useful is an Avalanche Forecast?
Simon Fraser University is collaborating with US avalanche centers to better understand how useful avalanche information is for planning your backcountry day. Please consider participating in this nationwide survey. It takes around 20 minutes. This research will help drive development of future avalanche forecast products. Thank you!

Tue, April 9th, 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
Wed, April 10th, 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
Wed, April 10th, 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

With sunny skies and warm temperatures in the lower elevations multiple wet loose avalanches have been observed in the last two days. I saw one glide avalanche on my drive south yesterday afternoon on Seattle Ridge just above road level. Small dry loose avalanches were reported yesterday on steep north facing terrain.

Glide avalanche on Seattle Ridge. Photo on left was taken around 11am and photo on the right at 5:30pm. 04.08.2024

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

The ridgetop winds have ramped up this morning from the east bringing wind slab avalanches back to our main concern today. There is not much snow available to be moved around this morning except on northerly aspects so the avalanche danger will begin at moderate and rise to considerable this afternoon if the mountains see the heavy snow showers that are forecast (6-8″ for Turnagain, 8-10″ for Girdwood/Portage/Placer and 4-6″ for Summit/Lost Lake).  The new snow is falling on crusty surfaces on most aspects except north where there is soft settled snow and some surface hoar. Small wind slabs should be easy for a person to trigger in the alpine, although these will grow in size as the day’s weather creates larger slabs towards the end of the day. The winds are strong enough that we could also find this problem in the treeline elevation band. Visibility may make it challenging to see recent avalanches but watch for blowing snow that forms “pillows” where it is being deposited. These are most likely to be found below ridgelines and on the lee side of gully features. Riding or jumping on a small test slope is a great way to assess how sensitive the snow is to a snowmachine or human trigger.

Storm slab: Bands of heavy snow showers are forecast today so areas that receive 10″ or more of new snow (likely Portage Valley), which includes all elevations, storm slab avalanches will become possible. This means shallow slab avalanches in areas sheltered from the wind.

Loose snow avalanches (sluffs): New snow sluffs will also be possible on all aspects in steep terrain.

Surface hoar was found yesterday in the Explorer Peak area on northerly aspects. Photo by Arnav Verma 04.08.2024

Forecast precipitation totals from 4am Tuesday to 4am Wednesday. Image courtesy of the National Weather Service Anchorage office. 04.09.2024

Weather
Tue, April 9th, 2024

Yesterday: Yesterday was a calm gorgeous spring day with sunny skies and variable wind averaging around 5 mph during the daylight hours gusting to 10 mph. Temperatures were in the mid 20s F at ridgetops and reached the low 40s F in the valleys. There was no new precipitation yesterday.

Today: A cold storm is arriving this morning which is forecast to bring bands of snow showers to sea level across our advisory areas through this evening tapering off tomorrow morning. Easterly ridgetop winds are averaging in the upper 20s mph this morning gusting in the 50s mph and should maintain this average until this evening.  The mountains should see some snow flurries this morning with the heaviest precipitation arriving midafternoon. Turnagain Pass should see 6 to 8″ of new snow by Wednesday morning while Girdwood and Portage could see closer to 8 to 10″. Summit and Lost Lake are looking on the lighter side of precipitation with 4 to 6″ forecast. Although temperatures could climb into the upper 30s F today at sea level, precipitation is forecast to remain as snow due to colder air aloft. Temperatures in the mountains should be in the upper 20s to 30 degrees F.

Tomorrow: Snow should taper off tomorrow morning followed by a partly to mostly sunny day. Temperatures look to climb into the 30s F and ridgetop winds are forecast to be 15 to 20 mph from the east gusting to 30 mph. Another system is on the way forecast to bring more precipitation on Thursday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 1 0.1 97
Summit Lake (1400′) 30 0 0 45
Alyeska Mid (1700′) 30 2 0.1 109
Bear Valley – Portage (132′) 34 trace 0.04
Grouse Ck (700′) 33 2 0.1 73

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 N 11 57
Seattle Ridge (2400′) 23 ESE 6 26
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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.