ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Friday December 7th, 2018
Posted by Heather Thamm on 12/07/18 at 7:00 am.
The Bottom Line
High Avalanche Danger
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Travel is not recommended today due to HIGH avalanche danger at all elevations. Large natural avalanches 2-3′ thick are very likely in the upper elevations of Turnagain Pass and Girdwood due to strong winds and heavy snow above 2000′. Wet avalanches are likely in the mid elevations and in channeled terrain below treeline.

PORTAGE: In Portage Valley where 4-5′ of snow is expected in the upper elevations avalanches could run their full length to valley bottoms. Avoid being near any avalanche paths.

SUMMIT LAKE: In Summit Lake where a very weak and shallow snowpack exists, storm slabs releasing naturally 1-2′ deep are likely today.  

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.
4. High
Below Treeline
/ Below 1,000'
Avalanche risk
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

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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

Today is a good day to avoid the mountains. Natural avalanche activity is expected in the mid and upper elevations where heavy snow and strong winds are forming storm slabs. Wet avalanches are expected in the mid elevations and may run to valley bottom in channeled terrain like Portage Valley. Ridgetop winds on Sunburst have already reached 60mph’s with a gust to 92mph at 6am. Rain/snow line is expected to fluctuate between 1000’ and 2000’ where a few inches of wet snow has alreday fallen this morning. In the Alpine above 2500′ Turnagain Pass and Girdwood could see an additional 15-24” of snow by late evening (1.5” – 2.0” of SWE.) Portage Valley will see double or triple this amount.  

Sadly we don’t have much of a snowpack below 2000′. Keep your fingers crossed temperatures stay on the cooler side and Treeline Zone receives some accumulation from this storm. If this is the case be aware of a slick bed surface above 1500’ where human triggered wet avalanches are likely. Travel is not recommended in avalanche terrain at all elevations and includes all run-out zone where avalanches from above may slide.

Strong winds and at least a foot of snow is expected in the upper elevations of Summit Lake today. A very thin snowpack and poor structure exist in this zone and natural avalanche activity is likely. Remember any obvious clues of instability are a reminder to avoid avalanche terrain; heavy precip, above freezing temps, blowing snow, natural avalanches, shooting cracks, and whumpfing. All of these are expected.

This is a graphical model from the National Weather Service for total amount of precip (Snow Water Equivelent) through 9pm tonight

 

 

A view of Seattle Ridge on Monday which shows very little snow below 1500′ 

 

As of 6:30am temps were staying just cool enough for precip to fall as snow at the road level (1000′) of Turnagian Pass. 

 

Mountain Weather

Yesterday: Light rain was observed below 1500′. Temperaturs were in the upper 30F’s near sea level and rain/snow line hovered between 1000′ and 1500′ most of the day. By mid afternoon East ridgetops winds increased to moderate in the afternoon and were strong by early evening. A few inches of wet snow and 0.5 € rain fell below 1000′ over the last 24 hrs, with most of it falling after midnight.  

Today: A fast moving low pressure system is pumping a lot of moisture into the Kenai Mountains and Western Chugach today. Strong Easterly ridgetop winds will remain in the 40-60mph range with gusts in 70-80s mph. Precipitation will fall as heavy rain in the lower elevations and rain/snow line may fluctuate between 1000′ and 2000′ throughout the day. At least 2′ of snow is expected in the upper elevations of Turnagain Pass and Girdwood and 4-5′ of snow is expected in Portage Valley above 2500′.    

Tomorrow: An active weather pattern will continue tomorrow and into early next week as a series of low-pressure systems and Southerly flow continue to impact our regions. A second storm will arrive tomorrow bringing a second round of warm temps, heavy precip and strong winds through Sunday morning. Unfortuantely this precip will be falling as heavy rain in the lower elevations.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34   3   .5   16  
Summit Lake (1400′) 32   1   .3   4  
Alyeska Mid (1700′) 33   3   .75 3  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   ENE   27   92  
Seattle Ridge (2400′) 30 ESE   16   44