ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Wednesday November 28th, 2018
Posted by Aleph Johnston-Bloom on 11/28/18 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 in the Alpine where triggering a slab avalanche is likely. Below 2500′ the danger is MODERATE. If there is any snow left triggering a wet loose avalanche will be possible and being in the runout of snow-covered slopes above should still be avoided today.

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

Special Announcements

The Friends of the CNFAIC have two scholarships dedicated to avalanche education. The funds generated to make these possible are in celebration of Rob Hammel and Amy Downing, their love and passion for the mountains, and to help others stay safe. We encourage you to read each one and apply if you fit the need, or pass along to someone who could benefit. Applications due on Dec 1st.

Rob Hammel Scholarship Fund   €“ For recreational users and professional avalanche workers.

Amy Downing Scholarship Fund   €“ For recreational users.

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 was much like the previous few days will an additional inch of water falling in the advisory area. Rain/snow line was between 2500′ and 3000′.  In the Alpine there has been significant snow load. Today triggering an avalanche in this elevation band is likely and avalanches could be large. There has been almost no visibility to see what has happened above the rain/snow line over the past 4 days and we have limited data on the overall snowpack structure. We do know that there were conditions for surface hoar and a melt-freeze crust before the storm. If you do venture into the mountains this is a day to proceed with caution and choose terrain carefully. Be on the lookout for signs of instability: recent avalanches, shooting cracks, and whumpfing

Water totals at the mid-elevation snow stations for this storm cycle from Saturday through Tuesday: 

  • Girdwood Valley at 1,700′:  5.1″ of water equivalent 
  • Turnagain Pass at 1,880′:  4.1″ of water equivalent
  • Summit Lake at 1,400′: 1″ of water equivalent 

If there is any snow left at treeline (2500′ and below) triggering a wet loose avalanche in the saturated snowpack is also possible before the temperatures cool down later in the day. 

Magnum and Cornbicuit, November 26, 2018. Photo: Wendy Wagner

 West and NW aspects of Tenderfoot, November 26, 2018. Photo: Heather Thamm

Mountain Weather

Yesterday:  Rain and snow throughout the day. Rain/snow line was between 2500′ and 3000′. An inch of water fell in advisory area. Winds were easterly 15-25 mph with gusts into the 40s. Temperatures were in the 40Fs at sea level and in the high 20Fs on Sunburst at 3800′.  

Today:  Light showers transitioning from rain to snow are forecast for today as cooler air moves into the area. Temperatures should slowly cool into evening starting in the mid 30Fs and dropping into the mid 20Fs. Chance of snow showers overnight. Winds will be easterly 5-15 mph with gusts in the 20s.  

Tomorrow:  Partly sunny with temperatures in the high 20Fs to low 30Fs. Light SW winds. There is some discussion about the next storm moving into the area over the weekend but timing, temperatures, and precipitation type are still uncertain.  

*Seattle Ridge weather station stopped collecting wind data at 10 pm.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  34 0    1.1  13
Summit Lake (1400′)  35 0    0.1  0
Alyeska Mid (1700′)  36 0   1.16    0

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27   NE    21  40
Seattle Ridge (2400′)  32     E *  7 *   32*