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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, March 4th, 2019 - 7:00AM
Expires
Tue, March 5th, 2019 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

A generally  LOW  avalanche danger remains for Turnagain, Girdwood and Portage areas. Although triggering a slab avalanche is unlikely, watch for sluffs on steep shaded slopes. Avoid travel under glide cracks and give cornices a wide berth.

SUMMIT LAKE / SILVERTIP:   More caution is advised south of Turnagain Pass as the snowpack is thin and harbors old weak layers.  

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Mon, March 4th, 2019
Alpine
Above 2,500'
1 - Low
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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.
Avalanche Problem 1
  • Normal Caution
    Normal Caution
Normal Caution
Normal Caution means triggering an avalanche is unlikely but not impossible.
More info at Avalanche.org

Today will be another day of Normal Caution (LOW danger). Clearing skies, temperatures generally in the 20Fs and calm winds should not have much impact on avalanche hazard.  With afternoon sunshine and as valley temperatures rise above freezing, low elevation solar aspects may see a little surface heating. 

“Don’t mess with the brown frown!” i.eavoid travel under glide cracks. Late last week and into the weekend we saw several glide cracks release into avalanches in the Girdwood Valley and at Turnagain Pass. Although many of these slides are on the smaller side and in areas not commonly traveled, one released Friday, March 1st on Seattle Ridge. As far as the older glide cracks we’ve been monitoring in popular areas such as Magnum, Lipps, Cornbiscuit, these do not appear to be moving as quickly. PSA: Help us keep track of these cracks and send us a photo! 

Things to keep in mind if you are headed into the backcountry:

  • Glide avalanches – These types of avalanches are highly unpredictable and not associated with human triggers. It’s always best to watch for and limit exposure under glide cracks.
  • Dry-loose sluffs – Watch your sluff on steep shaded slopes.
  • Cornice falls – As always, give cornices a wide berth. 
  • An outlier slab avalanche – Although it is unlikely a person could trigger a slab avalanche, the mountains can harbor surprises, especially in thin snowpack areas. Considering the consequences before entering into high consequence terrain and maintaining good travel protocol are good habits to keep on LOW danger days.

Surface conditions? A stout sun crust has been found on southerly facing slopes. Otherwise, 4-8″ or so of soft re-crystalized (near surface faceted snow) sits over a firmer base on shaded aspects and some sastrugi, old wind crust and/or rime crust can be found along ridgelines. In anticipation of the next storm, we are closely mapping the surface conditions as well as watching for new surface hoar growth. 

Sun crusts on Sunburst, 3-3-19. Photo: Allen Dahl

Closer view of the Seattle Ridge glide avalanche that occurred on March 1st and glide cracks to the right, 3-3-19. Photo: Allen Dahl

 

Additional Concern
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

South of Turnagain – Summit Lake and Silvertip zones:  For anyone traveling in this area note that a shallow snowpack with a generally poor structure exists. A variety of old weak layers (facets and buried surface hoar) sit in the mid and base of the snowpack. It is uncertain as to how reactive these layers are at this point and if they could produce a slab avalanche. Assessing the slab as well as the weak layer is important. The most suspect place to trigger an avalanche is steep terrain with old, hard wind slabs sitting on weak snow. 

Weather
Mon, March 4th, 2019

Yesterday:  Broken sky cover with a few flurries and some patches of sunshine. Temperatures ranged from the teens and 20Fs to the low 30Fs depending on elevation. Winds were very light and westerly. Skies were cloudy overnight with slightly cooler temperatures and light winds.    

Today:  Mostly cloudy skies becoming partly sunny by the afternoon. Temperatures in the 20Fs at upper elevations and the low 30Fs near sea level with calm winds. Skies will become cloudy again overnight and winds will be light with temperatures in the 20Fs.

Tomorrow: Mostly cloudy skies with a chance of snow showers, temperatures in the 20Fs and light easterly winds. We are still anticipating an overall pattern change and a storm this weekend. Stay tuned for details!  

MORE STATE OF THE SNOWPACK:   March 1st Snow Depth chart for Turnagain Pass. Time to do the Low-pressure  snow dance… Remember that’s counter clockwise!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  26 0   0   58  
Summit Lake (1400′)  23 0    0      28    
Alyeska Mid (1700′)  26  0      0      53    

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  17  W  1 5  
Seattle Ridge (2400′)  24  W   1   6  
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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.