ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Saturday December 8th, 2018
Posted by Wendy Wagner on 12/08/18 at 7:00 am.
The Bottom Line
High Avalanche Danger
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Travel is not recommended in avalanche terrain again today as a  HIGH  avalanche danger remains. Large natural avalanches are likely in the upper elevations as snowfall and winds continue. Wet avalanches are likely in the mid elevations and in channeled terrain below treeline.

PORTAGE:    Up to 5′ of snow has fallen in the high elevations, avalanches are still likely to run their full length to valley bottoms. Avoid being in avalanche paths.

SUMMIT LAKE:    A  very weak and shallow snowpack exists under the storm snow. Slab avalanches 1+’ deep will be very easy to trigger and may release naturally on steeper slopes.

4. High
Alpine
/ Above 2,500'
Avalanche risk
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4. High
Treeline
/ 1,000'-2,500'
Avalanche risk
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3. Considerable
Below Treeline
/ Below 1,000'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

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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

Yesterday’s quick moving and powerful storm brought feet of snow to the Alpine, inches of rain to sea level and 90mph winds to the ridgetops. The rain snow line bounced between 1,000′ and 1,500′ in most areas. Mostly wet snow and rain fell along Turnagain Pass and as of this morning, there is what looks to be an inch or two of snow surviving along the Pass. Rain and snowfall have decreased overnight but are on tap to pick up slightly again this evening. 

Storm totals at the mid-elevation snow stations (beginning Thursday night to 6am this morning)

  • Turnagain Pass at 1,880′:  1.5-2″ of water equivalent, roughly 1.5-2′ of snow above treeline
  • Girdwood Valley at 1,700′:  2.7″ of water equivalent, roughly 2-3′ above treeline
  • Summit Lake at 1,400′: 0.7″ of water equivalent (rain/snow mix along the road at Summit Pass), roughly 6-8″ of snow above treeline

Widespread avalanche activity was seen yesterday. Debris piles were observed running into snow free zones below 1,000′ in Girdwood and Portage Valleys as well as Seward. Although natural activity will be expected to decrease today, the mountains are still in shock and large avalanches are still likely in many areas. With additional snowfall tonight, natural avalanche likelihood could increase again. That said, today is another day to avoid avalanche terrain all together.  

Moose Mountain avalanches, outline of debris marked in orange. This is near MP 52 along the Seward Highway (Summit zone). Photo: Alex McLain

 

 

Upper Girdwood Valley, North side of Crow Creek Valley. Debris from avalanches above running to valley floor.

 

Seward’s Mt. Benson with several large debris piles from avalanche activity higher on the mountain. Photo: Jamie Lyons

 

Just enough snow to make it white along Turnagain Pass yesterday. This is Rookie Hill in the foreground looking at the base of Seattle Ridge, seen from the motorized parking lot. Photo: Will Brennen

Mountain Weather

Yesterday:   Heavy rain below 1,000′ and heavy snowfall above 1,500′ – a wintery mix in between these elevations. Snow and water totals above and below. Winds were strong out of the East, averaging in the 60’s mph with gusts into the 90’s. Temperatures were in the upper 20’s along the ridgetops and mid 30’s at 1,000′.  

Today:   Rain and snowfall has decreased overnight. Scattered showers should be seen around the region today and could pick up slightly tonight. Between .2-.3″ of rain below 1,000′ is forecast with 2-4″ of additional snow at the higher elevations today. Tonight snow line should lower and an additional 3-5″ of snow could be seen near sea level by tomorrow morning.   Ridgetop winds will continue from the east in the 25-30 mph range. Temperatures will be in the low 30’s at 1,000′ and mid 20’s along ridgelines through the day.  

Tomorrow:    Snowfall making its way to sea level will hopefully greet us in the morning as snow lines are forecast to lower. Snowfall should taper off by tomorrow morning bringing a break in storms before yet another wave of snow (and possibly rain at sea level) ushers in later on Sunday. Stay tuned!

*Seattle Ridge anemometer (wind sensor) reading uncommon wind direction during height of storm yesterday. Sensor is now rimed back over.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   14   1   30  
Summit Lake (1400′) 34   0   0.4   4  
Alyeska Mid (1700′) 33   2   1.92 4  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   NE   41   98!  
Seattle Ridge (2400′) 30   *WNW *25 66