ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Sunday April 21st, 2019
Posted by Aleph Johnston-Bloom on 04/21/19 at 7:00 am.
The Bottom Line
Considerable Avalanche Danger
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

The avalanche danger is CONSIDERABLE  above 1000′  due to strong winds and a mix of rain and snow impacting the area today. Natural avalanches are possible. Human triggered slab avalanches 1-3′ will be likely above 2000′. Below 2000′ where rain is falling, triggering  wet loose avalanches will be likely.  Extra caution is advised. 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.

WHITTIER:  Between 1-3 feet of new snow has likely fallen at the upper elevations in the Whittier Glacier region. Gale force winds and more snow and rain are in the forecast today. Heads up as natural avalanches are possible and large human triggered avalanches are likely.

LOST LAKE / SEWARD:  Extra caution is also advised in this region with new snow and rain in the forecast.

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

3. Considerable
Alpine
/ Above 2,500'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
3. Considerable
Treeline
/ 1,000'-2,500'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
0. No Rating
Below Treeline
/ Below 1,000'
Avalanche risk

Special Announcements

  • Advisories:  For the remainder of April, avalanche advisories will be posted 4 days/week (on Tues, Thur, Sat and Sun). 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!
  • Headed to Hatcher Pass? Be sure to check out the most recent avalanche observations HERE.
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

The mountains are forecast to get another foot of snow today with easterly winds gusting into the 50s. Since Friday morning upper elevations have received between 10-30″ of snow favoring Girdwood. Natural storm slabs 1-3′ will be possible in the Alpine and human triggering will be likely on slopes 35 degrees and steeper. High elevation northerly aspects are the most suspect for poor bonding as the new snow fell onto weak older snow and possibly surface hoar. Slabs will be the deepest on wind-loaded slopes. Visibility will be limited so avoid runout areas where natural avalanches could fall from above.  Look for signs of recent avalanches, shooting cracks and drifted snow, and listen for whumphing.

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 last weekend failing on this layer. There is a chance that this layer could be overloaded, resulting in an avalanche stepping down deeper in the snowpack and is another good reason to avoid steep northerly slopes in the Alpine today!

Choose terrain wisely, visibility will be limited and natural avalanches will be possible. Tincan yesterday 4-20-19.

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

Rain falling on snow today below 2000′ could initiate natural wet loose avalanches. These will be larger in areas with the more snow prior to the rain. A skier or a machine on a steep slope may also trigger these. As the snowpack becomes saturated wet sluffs may gouge deeper. Watch for roller balls and sinking into punchy wet snow.

CORNICES: There are still large cornices along ridge tops. Wind and snow today will make them even larger. Give them lots of space as they can break farther back than expected an could release naturally.

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

Watch for roller balls as snow becomes a saturated! 

Mountain Weather

Yesterday:  Skies were broken in the morning and became mostly cloudy. There were light snow and rain showers throughout the day. The rain/snowline was around 700′. Temperatures were in the low 40Fs at sea level, 30Fs in the mid elevations and 20Fs at ridgetops. Winds were easterly gusting into the 20s during the day, increasing to gusts in the 40s overnight. 0.5-1.0″ SWE fell in the early morning hours again favoring Girdwood with temperatures in the high 30Fs to mid 20Fs.

Today: Rain/snow  could be heavy at times today. An inch of water is forecast to fall. This could translate to over a foot of new snow at upper elevations. Rain/snowline is forecast to be 1600′ but may rise to 2000′. Easterly winds will be 20-40 mph gusting into the 50s. Precipitation and winds will decrease overnight.

Tomorrow: Mostly cloudy skies with light rain/snow showers. Winds will be northerly 5-15 mph gusting into the 20s. Temperatures will be in the 30Fs dropping to the 20Fs later in the day. Snow may fall to sea level overnight into Tuesday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 8 0.6 72
Summit Lake (1400′) 34 1 0.1 22
Alyeska Mid (1700′)  34 6 0.5  66

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  28 NE 15 42
Seattle Ridge (2400′)   27 SE  8 18