Wednesday-Saturday 2/7-2/10

Issued: Wed, Feb 07, 2018 at 8AM

Expires: Sun, Feb 11, 2018

You are most likely to trigger a slide where new snow has drifted into deeper pockets. 6” of this fresh snow can drift into a 2′ slab with winds as little as 10mph.

  • Shooting cracks/mini isolated avalanches under your skis/machine = Red Flag.
  • Recent avalanches on slopes of similiar angle/aspect/elevation to terrain you plan to play on=BIG RED FLAG.

Above 2,500ft Moderate

1,800 to 2,500ft Low

Below 1,800ft Low

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

Wednesday Thursday Friday
& Saturday
2-moderate 2-moderate

DANGER SCALE

 

WIND SLAB:
Elevation:
   Above 2000′
Aspect:  
 Lee of ridges, gullies, ridgetops
Terrain: 
  All terrain exposed to wind
Sensitivity:
   Responsive
Distribution:   
Specific
Likelihood (Human Triggered): 
Possible
Size:   
Small – Large
Danger Trend:
 Steady
Forecaster Confidence:
   Good

PERSISTENT SLAB:
Elevation:
   Above 2500′
Aspect:
   All
Terrain: 
  35+ degrees steepness
Sensitivity:
   Stubborn
Distribution:   
Specific
Likelihood (Human Triggered):   
Possible
Size:   
Small – Large
Danger Trend:
   Steady (decreasing? Need more data) 
Forecaster Confidence:
   Poor

AVALANCHE PROBLEM SCALE DESCRIPTORS:
Sensitivity: Non-reactive, Stubborn, Responsive, Touchy
Distribution: Isolated, Specific, Widespread
Likelihood: Unlikely, Possible, Likely, Nearly Certain
Size: Small, Large, Very Large (size scale <here>)
Danger Trend: Increasing, Steady, Decreasing
Forecaster Confidence: Good, Fair, Poor

LIST OF AVALANCHE PROBLEMS <here>

SNOWPACK DISCUSSION: 

New soft windslabs to knee deep drifting the few inches of Feb 6 new snow are poorly bonded to the old snow.

Cold temperatures continue to promote the growth of surface hoar in wind protected areas and near surface faceting, sugar snow, across the Chugach range. When this bit of new snow is buried with subsequent snowfall (Sun? Mon? Feb 11-12?) it will likely become a future weak layer.

Prior to this new snow we had a 2+ week dry spell, with extreme winds (80+MPH). These winds affected almost all of the landscape on Thompson Pass. Some areas were loaded with very thick wind slabs. Wind slab avalanches have been sliding naturally (estimated) 2′-5′ deep, 500′ wide, and 1000′ vertical. Snowmachines have been cutting very small windslab slides 1”-1′ down, releasing directly under the sled. These small slides isolated under a snowmachine, in combination with the large naturally occurring avalanches, bring us to the conclusion that D2 (can kill a person) human triggered avalanches are possible.

Previous to the Jan.13-16 storm there were concerns of a persistent weak layer about 1-2’ under the snow surface. This persistent weak layer (surface hoar and/or near-surface facets) is now buried 1′-6’ down.  Our snowpack tests indicate that this layer is persisting and remains a concern.  We encourage you to dig for and test this layer, especially above 3000′.  Jan.26 on a NW aspect across from Rice Mountain at 3200′, we found this layer 28″ (70cm) below the snow surface and it was stubborn to trigger. This layer was confirmed by another party Sunday January 28 closer to Thompson Pass. It was found 32″ (80cm) down and propagated when tested.

Below 2000′ (the rainline from the Jan.13-16 storm) the snow is frozen in place with a beefy crust.

Recent Avalanche Activity

February 5: Two hard slab size D2 off Oddysey at Milepost 27 and one impressive hard slab size D2 with a crown hundreds of yards long off Little Girls above the Worthington Flats at Milepist 29.

January 28: several size 1-2 windslab avalanches observed lee to north outflow wind, mostly off ridgelines and gully walls above 3000′ through the Thompson Pass corridor.

Jan.28, 2018 Natural windslab avalanche on west facing gully wall above MP 33. Ryan Van Luit photo.

Wind transport Jan.28, 2018. Ryan Van Luit photos.

 

 

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  0 / 20
Ridgetop Wind Forecast (direction/mph): NE / 25-50
Snowfall (in): 0
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction   8 / NE  35 / NE
Max Wind Gust (mph) / Direction  20 / NE  45 / NE
Temperature Min / Max (*F)  20 / 28  -1 / 5

Weather Forecast:     Becoming sunny and beautiful again for the remainder of the week with our lovely screaming northeasterly outflow winds to 70 mph and temperatures below zero F, especially north of Thompson Pass until the next snowflakes fall Sunday February 11.

Additional Info & Media

SNOW HISTORY: Valdez 2/7 AM Thompson Pass 2/7 AM
24 Hour Snow / Water Equiv. 1.5”/ 0.1″ 2″ / 0.1″
Storm Snow /Water Equiv. (2/6) 1.5” / 0.1″ 3″ / 0.2″
Current Snow Depth 25″ 73″
February Snow / Water Equiv. 1.5″ / 0.1″ 3″ / 0.2″
Total Winter Snowfall / Water Equiv. 79″ / 22.15” 293″ / 30.5″
Snowload in Valdez 39.5 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS / STORM TOTAL (Jan.13-16) / STORM WATER EQUIV.:
Nicks Valley at 4200 ft (in): 0″ / 22″ / ?”
Upper Tsaina at 1750 ft (in): 0″ / 19″ / 2″
Sugarloaf at 550 ft (in): 0″ /rain” / ?”
SNOW DEPTH & WATER SURVEY (2/5/2018) Depth Snow Water Equivalent
Milepost 2.5 Valdez  22″  7.6″
Milepost 18 32.5″ 9.6″
Milepost 29 Worthington Flats 62″ 19.4″
Milepost 37 Tsaina River bridge 52.6″ 16.4″
This survey is done the first week of each month.

Weather Quicklinks:

 

SNOW CLIMATE ZONES:

  • coastal-zone-iconMaritime (Coastal) – from the Port of Valdez to Thompson Pass, all waters flowing into Valdez Arm and everything south of Marshall Pass.
  • intermountain-zone-iconInter-mountain (Transitional) – between Thompson Pass and Rendezvous Lodge.
  • interior-zone-iconContinental (Interior) – the dry north side of the Chugach (north of 46 Mile, including the Tonsina River).

Photo of Thompson Pass

thompson-pass-ski-runs

Interactive Map of Valdez Forecast Areas w/ Many Resource Layers (Trevor Grams)

climate-zones-topoclimate-zones-satellitegoogle-earth1

Run Map of Thompson Pass Area (Sean Wisner) (2MB download)
VAC Run Map Thompson Pass

NEWS: Our region is “one of the snowiest places on earth” – Serendipity / Rendezvous snowfall record set in 1963 <here>.

Free smart phone avalanche forecasts at: http://www.avalancheforecasts.com/

Posted in Continental Forecasts, Intermountain Forecasts, Maritime Forecasts.
Pete Carter

Forecaster: Pete Carter