ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Tuesday April 23rd, 2019
Posted by Aleph Johnston-Bloom on 04/23/19 at 7:00 am.
The Bottom Line
Moderate Avalanche Danger
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

The avalanche danger is MODERATE  above 1000′.  Human triggered slab avalanches 1-3′ are possible on slopes 35 degrees and steeper. Watch for warming and wet loose activity on solar aspects if the sun makes an appearance. Evaluate snow and terrain carefully, ease into steep terrain and look for signs of instability. As always, give cornices a wide berth and limit travel under glide cracks.

PORTAGE VALLEY:  Cornice fall and/or avalanches from above have the potential to send debris to valley bottoms. Traveling along summer hiking trails, such as the Byron Glacier Trail with steep slopes overhead is not recommended on rainy/snowy days or on sunny afternoons. Portage Valley received over 4′ of snow at upper elevations and cornices are looming large.

WHITTIER:  Between 2-4 feet of new snow has likely fallen at the upper elevations in the Whittier Glacier region.   Heads up as there is limited snowpack information for this area. Large human triggered avalanches are possible and extra caution is advised.

LOST LAKE / SEWARD:  There is also limited snowpack information for this region as well. Ease into steeper terrain and look for signs of instability.

WEDNESDAY AVALANCHE OUTLOOK:
No avalanche forecast will be issued tomorrow.  Avalanche danger is expected to be similar to today. Pay attention to changing conditions and look for signs of instability.    

2. Moderate
Alpine
/ Above 2,500'
Avalanche risk
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2. Moderate
Treeline
/ 1,000'-2,500'
Avalanche risk
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
0. No Rating
Below Treeline
/ Below 1,000'
Avalanche risk

Special Announcements

  • Advisories:  Our last avalanche advisory will be posted Thursday April 25th. The avalanche center will close for the season on Saturday, April 27th when we will post our springtime tips. Thank you everyone for tuning in! Big thanks to all of our observers and the local avalanche professionals that share information with the CNFAIC.
Avalanche Problem 1
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
  • TYPE
    Storm Slabs
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

#hellowinterwherewereyouinmarch. An active weather pattern starting Thursday April 17th brought snow and rain to the area and total water amounts ranging from 3.6″ at the Alyeska top station, 4+” in Portage, 2.1″ at Center Ridge on Turnagain Pass to 1.1″ in Summit Lake. This equates to upper elevations receiving between 10-40″ of snow favoring Girdwood and Portage. Temperatures cooled Sunday afternoon into Monday and brought light snow to sea level. Sunday there were strong sustained easterly winds that gusted as high as 78 mph on Sunburst. These eased off that evening and were mostly light yesterday. Triggering a 1-3′ slab will be possible on slopes 35 degrees and steeper today. Slabs will be the deepest on wind-loaded slopes. High elevation northerly aspects are the most suspect for poor bonding as the new snow fell onto weak older snow and possibly surface hoar. Warm temperatures for much of the weekend followed by cooling will have helped stabilize the new snow. However, the snowpack is untested and it will be important to look for recent avalanches, shooting cracks and drifted snow, and listen for whumphing. Ease carefully into steeper terrain and use safe travel protocols. There is some uncertainty today about cloud cover and direct sunshine. Pay attention to changing surface conditions and watch for roller balls. On solar aspects warming may increase instability and likelihood of triggering.

PERSISTENT SLABS: Steep northerly slopes above 3000′ also harbor buried surface hoar and near surface facets that were buried 1-2′ deep on April 5th. Two human triggered avalanches occurred just over a week ago failing on this layer. There is a chance that triggering an avalanche in the storm snow on a north aspect above 3000′ could step down resulting in a large avalanche breaking deeper in the snowpack.

Sunburst wind profile over the weekend. Pay attention to loading patterns and watch for cracking. 

Wintery weather on Tincan, Sunday April 21st. Photo: Ray Koleser

Avalanche Problem 2
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.
  • TYPE
    Wet Loose
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

There is a chance that the sun could come out today or tomorrow and warm up the new snow. If this happens watch for signs that the surface is becoming wet. Roller balls may build into loose wet avalanches. Due to the amount of new snow these could become large as they entrain snow. Change aspects if the snow starts to show signs of warming and be especially suspect of being on or under steep, rocky, southerly terrain.

CORNICES: There are still large cornices along ridge tops. They will have grown during the storm and may be tender. Give them lots of space as they can break farther back than expected.

GLIDE AVALANCHES: It’s been over two weeks since our last known glide avalanche, but keep in mind glide cracks are continuing to creep downhill. As always, limit traveling under their runout. They are unpredictable and can avalanche at any time.

Mountain Weather

Yesterday:  Skies were mostly cloudy with pockets of good visibility. There were snow showers on and off throughout the day with snow falling to sea level and a few inches of accumulation. Winds were variable gusting into the 20s. Temperatures ranged from in the high teens and 20Fs at upper elevations to right around 30F at sea level. Overnight temperatures cooled slightly and winds remained light.

Today:  Mostly to partly cloudy skies. There is a chance of snow showers. Winds will be light and easterly. Temperatures will be in the 30Fs to 40F at sea level and in the 20Fs at upper elevations.   Overnight snow showers are likely, temperatures will cool slightly and winds remain light.

Tomorrow:  Mostly to partly cloudy skies. Slight chance of snow showers. Winds continue to be light and temperatures will be similar to Tuesday. Looking ahead there is sunshine and warmer temperatures on tap for Thursday and Friday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27  1 0.1 74
Summit Lake (1400′)  27  2 0.2 21
Alyeska Mid (1700′) 27  2 0.19 69

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  18 NE 4 24
Seattle Ridge (2400′)  23 SW  3 8