Tuesday-Friday 1/3-1/6

Issued: Tue, Jan 03, 2017 at 8AM

Expires: Fri, Jan 06, 2017

Upper elevations have had 24 hours of above freezing temperatures due to an inversion.  Old weak layers may be reactivated given the persistent weak layer buried 2-3′ deep. There may not be signs of instability until the large destructive avalanche is triggered by a heavy load.

Travel with caution using good habits:

  • all riders have a functioning beacon, probe, and shovel (& floatpack)
  • avoid slopes with rocky trigger points and thin areas with windslab
  • avoid slopes with terrain traps like cliffs, gullies, and creek ravines
  • one rider on slope at a time
  • group up out of harm’s way, beyond the run out or at the side, on high ground
  • review your day – where could you have triggered a slide?

Above 2,500ft Considerable

1,800 to 2,500ft Moderate

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

TUESDAY WEDNESDAY THURSDAY & FRIDAY

DANGER SCALE

WET AVALANCHES:
Elevation: 
Above 2500′
Aspect: 
all
Terrain: 
slopes steeper than 30, especially under or near rocks and cliffs
Sensitivity: 
Responsive
Distribution: 
Specific
Likelihood (Human Triggered): 
Possible
Size: 
Small to Medium
Danger Trend:
Increasing with prolonged temperature inversion
Forecaster Confidence: 
Fair

WIND SLAB:
Elevation: Above 1800′
Aspect: mostly south and west
Terrain: Near ridgelines, gullies and rollovers
Sensitivity: Responsive
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Steady
Forecaster Confidence: Good

PERSISTENT SLAB:
Elevation: Mostly above 2500′
Aspect: All
Terrain: Steep rocky slopes where facets exist under old and between windslab, especially interior of Thompson Pass
Sensitivity: Stubborn
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Medium
Danger Trend: Increasing with continued windloading and temperature inversion
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, Medium, Large, Very Large (size scale <here>)
Danger Trend: Increasing, Steady, Decreasing
Forecaster Confidence: Good, Fair, Poor

LIST OF AVALANCHE PROBLEMS <here>

SNOWPACK DISCUSSION: This morning the lingering temperature inversion is impressive. At the Tsaina snotel (1750′) it is -13F, at Nick’s Valley (4200′) it is 38F. These two stations are just 1.88miles apart, but the difference in temp drastic; 51 degrees farhenheit! These above freezing temps in the alpine will affect the snow surface and possbily reactivate old weak layers. The cold in the low ground will continue to weaken the snowpack by faceting. Surface hoar might be growing.

In exposed areas and channeled terrain, the north wind has picked up (day 3 of an outflow wind event) and is recycling and drfiting snow again. Expect windslab and sastrugi to 2 feet deep.  While this windslab is less touchy than when it was fresh snow being transported, the hard slab can let you get out on it further before it breaks and can produce a larger, deeper slide.

coastal-zone-iconMaritime (Coastal):
Valdez town received 12″ out of the Dec.30-31 storm. With more snow and warmer temperatures, the maritime zone has a generally more uniform snowpack. Although more stubborn, we can’t write off upper elevations harboring buried weak facets near the ground.

intermountain-zone-iconInter-mountain (Transitional):
Early season facets at the ground and between layers of windslab are still a concern. In some areas tests show sudden collapse with propagation potential; see observations from the past week. It is not out of the picture for heavy loads such as a snowmachine or multiple machines to trigger a wind loaded slope and have it step down to persistent weak layers, increasing the avalanche size and destructive potential. Today’s continuing above freezing temperature inversion in the alpine will change the snow surface, and could waken deeper activity.

Very easy failure at top of weak facets when isolating column up Nicks @ 4200'

Very easy failure at top of weak facets when isolating column up Nicks @ 4200′

Propagation supported up Nicks Valley @ 4200': PST 40/100 (end)

Propagation supported up Nicks Valley @ 4200′: PST 40/100 (end)

interior-zone-iconContinental (Interior):
More interior beyond Mile Post 37 and out past Billy Mitchell, the snowpack is thin and weaker. Recent avalanches stepped down to ground. This early season persistent slab problem will not go away quickly. Today’s continued temperature inversion could trigger some avalanche activity on steep, unsupported slopes where the snowpack is thin.

Find more photos and observations at the bottom of the page. Sharing your observations helps others make informed decisions.

Recent Avalanche Activity

Please report avalanches you see or trigger. We have a lot of uncertainty about the persistant slab problem and any activity or signs of unstable snow provides more clues for figuring out patterns of instability.

coastal-zone-iconMaritime (Coastal):

  • A couple new loose size 1-2 avalanches out of steep rocks Jan.2 above 3000′.

intermountain-zone-iconInter-Mountain (Transitional): Significant avalanche activity during the Dec.30-31 storm. Avalanches inland of Thompson Pass proved there is still a dangerous buried weak layer (facets at the ground) that has a lower probability of triggering, but high consequence due to hard windslab to 2-3 feet overtop.

  • Dec.31 A couple human triggered destructive size 1-2 windslab avalanches on the steep slopes of the road run
  • Dec.30 A couple destructive size 2 (D2) storm slab avalanches pulled out on North face of Berlin Wall: stepped down to rocky ground in places (crown depth estimated ~4 feet) and hit the glacier.
  • Dec. 30 Wind loaded south face above Mile Post 37 near 3 Pigs: D2 slab pulled out of steep and rocky rollover and immediately stepped down to ground (see photo)
  • Dec.30 South facing steep, rocky gully at Mile Post 42 and ran to aldered apron

interior-zone-iconContinental (Interior):

  • Dec. 30 D2 storm slab avalanche pulled out to ground mid south slope of Mt Tiekel over Mile Post 46

 

 

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  36/ 44 inversion!
Ridgetop Wind Forecast (direction/mph): NE / 10-40
Snowfall (in):  0
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 5 / E 30/ NE
Max Wind Gust (mph) / Direction 14/ NE 40 / NE
Temperature Min / Max (*F) 22 / 31 3 / 22

Weather Forecast: Continued clear skies. A strong north wind has been blowing for three days in channeled terrain and at ridgetops. In wind protected areas a temperature inversion developed Sunday afternoon, keeping temperatures above freezing for more than 24 hours now.  While this ridge of high pressure stays over us, the cool air will continue to pool in the valleys while warm air rises. Where it is windy, there are vortexes of mixing that feel strange, a cool breeze and five minutes later a zephyr of hot air. There is no significant precipitation in the forecast.

Additional Info & Media

SNOW HISTORY: Valdez 1/4 AM Thompson Pass 1/3 AM
24 Hour Snow / Water Equiv. 0” /0.0” 0″ /0″
Storm Snow /Water Equiv. (12/30-12/31) 5” /0.68″ 18″ /1.6″
Current Snow Depth 29.5″ 32″
January Snow / Water Equiv. 0″ /0″ 0″ / 0″
Total Winter Snowfall / Water Equiv. 95.9″ / 8.16” 143″ / 14.4″
Snowload in Valdez 23 lbs/sq. ft.

img_20161228_130954img_20161228_130730

Photos of our new Nicks Valley Weather Station Python to the east, Berlin Wall to the west.

SNOWFALL for LAST 24 HRS at OTHER STATIONS:
Nicks Valley at 4200 ft (in): 0″
Upper Tsaina at 1750 ft (in): 0″
Sugarloaf at 550 ft (in): 0″
SNOW DEPTH & WATER SURVEY (1/3/2017) Depth Snow Water Equivalent
Milepost 2.5 Valdez  -″  -″
Milepost 18 -″ -″
Milepost 29 Worthington Flats 44″ 9.9″
Milepost 37 Tsaina River bridge 33.8″ 5.6″
This survey is done the first week of each month.

Weather Quicklinks:

  • NWS forecast for Northeast Prince William Sound <here>
  • NOAA NWS spot forecast for Thompson Pass <here>
  • Thompson Pass RWIS weather station <here>
  • MP 30 Nicks (Happy) Valley weather station at 4200 feet <here> (scroll to Nicks Valley)
  • Valdez Glacier UAF weather station at 6600 feet <data here> <map here>
  • Further weather resources <here>

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 VAC Forecasts.
Sarah Carter

Forecaster: Sarah Carter