ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Thursday April 11th, 2019
Posted by Heather Thamm on 04/11/19 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 today above 2500′. Triggering a wind slab up to 12 € thick will be possible on steep leeward features due to strong wind and new snow. Below 2500′ the avalanche danger is MODERATE where triggering a wet loose avalanche is possible. Avoid traveling below glide cracks and cornices. Should the sun make an appearance later in the day, natural wet loose activity in the alpine on solar aspects will be possible.  

PORTAGE VALLEY:  There is very little snow below 1000′, but Summer trails with large steep slopes directly overhead, such as the Byron Glacier Trail, provide easy access for accidentally being in a dangerous place. Today’s strong winds and heavy precipitation could trigger cornice fall or a wet avalanche into the valley below. Travel in these areas is not recommended.

3. Considerable
Alpine
/ Above 2,500'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
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
Avalanche Problem 1
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.
  • TYPE
    Wind Slabs
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

A storm has moved into our region bringing strong winds, rain and heavy snow above 2000’. Overnight Easterly ridgetop winds increased into the 30s mph with gusts in the 60s mph. Winds will remain strong all day. An estimated 2-4” of snow has fallen overnight in the upper elevations of Turnagain and Girdwood. Portage has seen heavy rain. An additional 6-12” of new snow is expected in the upper elevations (0.6-0.8” of rain) for Girdwood and the North end of Turnagain Pass. Interior areas will see less precipitation. Wind slab size will depend on how much snow falls in the area you are traveling.

New snow will be falling on a variety of slick surfaces and bonding may be poor. Today’s visibility will make for difficult travel in the alpine due to blowing snow. Be on the lookout for shooting cracks and avoid slopes steeper than 35 degrees. Look for pillowed snow along ridgelines and be cautious of fresh drifts. Small natural wind slabs are possible in very steep channeled terrain due to the intensity of wind. Cornices will also be growing and could release naturally.

WET LOOSE: In the lower elevations below 2000’ triggering a wet loose avalanche will become possible as rain starts breaking down surface crusts. If the snow becomes wet and unsupportable avoid steep terrain features and terrain traps. **Keep in mind it’s springtime and be ready for wet loose activity in the alpine if the sun comes out and starts heating up the new snow. This is more likely further from the coast as the storm front moves out of the region.

Slick Crusts exist on W-S-E aspects in the alpine (left photo) and a 4-6″ of soft snow is sitting on near surface facets and buried surface hoar on some North aspects (photo on right.) 

 

 

Corniced Ridge in Girdwood Valley – Cornices will be growing today with strong wind and new snow. Give these features lots of space along ridge lines and avoid being under them.

Additional Concern
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
  • TYPE
    Glide Avalanches

Although it has been several days since we have seen a glide crack release into an avalanche, avoiding/limiting travel under cracks is prudent! They can release at anytime, are completely unpredictable and can be very destructive. Identify existing cracks and plan your route to avoid being under a glide.

Mountain Weather

Yesterday: Skies were partly cloudy in the morning becoming mostly cloudy later in the day. Temperatures reached the mid-40Fs at sea level. Upper elevation temps were in the mid-20Fs to low-30s. Ridgtop winds were 5-15mph from the East building overnight into the 30mph with gust in the 60s. Rain started falling overnight and .2 € of SWE was recorded in Turnagain Pass with 1″ of wet snow. Bear Valley in Portage has recorded .7 € of rain in the last 24hrs. Rain/snow line is estimated around 1800′.

Today: In the upper elevation 6-12 € of snow is expected in the alpine, with 0.6-0.8 € rain at lower elevations. Rain/snow line should be around 2000′. Areas further from the coast will see less precip today. Easterly ridgetop winds are expected to be 35-50mph with stronger gusts. Temperatures at sea level will be in the mid-40Fs, temps along ridge tops may reach the upper-20Fs. As the storm moves out of the area, winds and precip will decrease overnight.

Tomorrow: Scattered rain and snow showers are expected – light rain below 2000′ and a few inches of snow possible in the upper elevations. Easterly Ridgetop winds will be 10-20mph.Temperatures at sea level will be in the mid-40Fs and ridgetop temps in the low-30Fs during the day.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36   1   0.2   62  
Summit Lake (1400′) 38   0   0   18  
Alyeska Mid (1700′) 37   1   .27   55  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   ENE    18 71  
Seattle Ridge (2400′) 29   SE   13   31