ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Saturday April 20th, 2019
Posted by Wendy Wagner on 04/20/19 at 7:00 am.
Avalanche risk
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  for avalanches composed of the 6 – 12+” of new snow. On Northerly slopes above 2,500′ dry slab avalanches 6-18+” thick will be possible to trigger. On Southerly facing slopes and all aspects below 2,500′ wet loose avalanches are possible with daytime warming and solar radiation. Give cornices a wide berth and limit travel under glide cracks. The avalanche danger is expected to rise overnight and into Sunday as a warm storm moves in.

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 1-2 feet of new snow has likely fallen at the upper elevations in the Whittier Glacier region. Heads up as large human triggered avalanches are possible.

LOST LAKE / SEWARD:  Similar to Turnagain, dry slab avalanches could be a concern on high elevation northerly slopes.

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:  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!
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

Anywhere between 6-16″ of new dry snow has fallen over the past 36 hours across the region. Girdwood Valley seemed to have picked up the most snow, with over a foot accumulating at the high elevations. Turnagain Pass and Summit Lake have both seen around 6-8″ of new snow. Easterly ridgetop winds have been 15-25mph, which is enough to load leeward slopes. That said, avalanche concerns will be relegated to the new snow. How much snow fell in the area you travel, how much wind loading occurred and how the new snow is bonding to the underlying surfaces are the questions today. High elevation northerly aspects are the most suspect for poor bonding as the new snow fell onto weak older snow and possibly surface hoar. If you are headed out today in hopes of the clouds breaking, keep the following in mind:

  • Dry slab avalanches up to a foot thick could be triggered on steep northerly slopes
  • Wind loaded slopes are more concerning as slab depths could be greater (1-2′ feet)
  • Listen/feel for collapsing in the new snow
  • Watch for cracking in the new snow 
  • Quick hand pits are great ways to assess the new snow/old snow bonding
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

On all Southerly facing slopes and slopes below 2,500′ we can expect the new snow to stick rather well to the old soft/warm crusts. The concern here will be daytime warming and sunshine. Roller balls and wet loose sluffs should be expected as the new snow heats up and begins to roll and sluff off the mountainsides. The size of potential sluffs will be determined by the amount of new snow. Wet sluffs could become quite large and dangerous on slopes with up to a foot or more of new snow.

CORNICES: There are still large cornices along ridge tops. Give them lots of space as they can break farther back than expected. 

GLIDE AVALANCHES: It’s been close to 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. 

Mountain Weather

Yesterday:   Roughly 6-10″ of new snow fell over the region at all elevations late Thursday and early Friday morning, favoring Girdwood Valley. Light showers continued through the day adding another 1-3″. Ridgetop winds over the past 24-hours have been easterly 15-25mph with gusts to 40mph. Temperatures have been in the 20’sF along ridgetops and near 30F at 1,000′.  

Today:   Clearing skies and lingering clouds are expected today before a third round of precipitation pushes in tonight. Ridgetop winds should be in the 10-20mph range from the east today and bumping up to the 30’s tonight. Temperatures are on a warming trend and may reach 40F at 1,000′ today with ridgetops in the upper 20’sF.  

Tomorrow:   Stormy wet weather is on tap. Rain up to 1,500 – 2,000′ is expected tomorrow with 6-12″ of snow above this. Up to 16″ of snow could fall in favored areas such as Portage Valley and Girdwood. Ridgetop easterly winds will be in the 30-40mph range with gusts over 50. Unsettled and wet weather looks continue into the workweek.


Thanks to our NWS partners for their graphic of QPF (Quantitative Precipitation Forecast), which is the water amount expected through Sunday. A general rule of thumb is 1″ of water = 10″ of snow. Of course it has to cold enough for snow and this event is expected to bring rain up to 1,500′ with snow falling at the higher elevations.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34   1   0.2   65  
Summit Lake (1400′) 32   3   0.3   20  
Alyeska Mid (1700′) 30   3   0.4   62  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20   SE   15   40  
Seattle Ridge (2400′) 25 *N/A *N/A   *N/A