Sunday – Wednesday

Issued: Sun, Dec 11, 2016 at 8AM

Expires: Wed, Dec 14, 2016

The north wind has and will continue to transport snow onto south and westerly aspects. Avoid steep windloaded slopes.

We have weak sugar snow under wind slab. It is possible for humans, especially heavy loads like multiple people or machines, to trigger wind slab avalanches large enough to hurt or bury. The harder the slab the further it can propagate, with a possibility of step down to deeper persistent weak layers.

Above 2,500ft Moderate

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

GENERAL DANGER RATING OUTLOOK

SUNDAY MONDAY TUESDAY & WEDNESDAY
2-moderate 2-moderate 2-moderate

DANGER SCALE

WIND & PERSISTENT SLAB:

Elevation: Above 1800′ in the alpine
Aspect: All where exposed to wind, particularly south and west
Terrain: Ridgelines, rollovers, cross-loaded features
Sensitivity: Stubborn
Distribution: Specific steep features
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Steady
Forecaster Confidence: Fair
Details: This problem will continue with north wind and cold temps.

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: Ten inches of cold dry snow fell in town and port-side mountains Dec. 8-9. Thompson Pass and further interior only received 2 inches. In wind exposed areas, the northerly outflow wind moved this new snow, adding another layer of windslab.

Cold temperatures are weakening bonds throughout the snowpack. Expect sugar snow (facets) between layers of windslab, around bushes and rocks, and at the ground. Yesterday tests showed failure at these interfaces: the boundary of new and old windslab, old faceted crust from Nov.12, and within facets at the ground.

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

Recent Avalanche Activity

  • Over the last week, several windslab avalanches to size 2 have released in steep terrain at rollovers, ridgelines, and gully walls.
  • December 9 Loose, dry sluffs in steeps near the Port.
20161209 Loose Dry & Transport in the Port where more storm snow fell relative to Thompson Pass

20161209 Loose Dry & Wind transport near the Port

 

20161204 North Odyssey Wind Slab Triggered by Snow Machine

20161204 MP 26 North Odyssey Wind Slab Triggered by Snow Machine & Rider

 

20161203 Bald Boy & Adjacent Sympathetic

20161203 Triggered from below

20161203 MP 26 Triggered from below: Odyssey Lake

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  -3/27
Ridgetop Wind Forecast (mph):  8-40/ NE
Snowfall (in):  0
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 15 / NE 40 / NE
Max Wind Gust (mph) / Direction 28 / ENE 57 / NE
Temperature Min / Max (*F) 16 / 29 -8 / 6

A ridge of high pressure will continue through the week. Near zero F temps at Thompson pass with slight warming trend by late week as the next storm approaches. Strong north wind to continue in passes and glaciated river valleys. No precipitation until clouds move in Thursday.

Additional Info & Media

SNOW HISTORY: Valdez 12/11 AM Thompson Pass 12/11 AM
24 Hour Snow / Water Equiv.  0” /0″ 0″ /0″
Storm Snow /Water Equiv. (12/8-12/9) 10” /0.6″ 2″ /0.1″
Current Snow Depth 20″ 18″
December Snow / Water Equiv. 32″ / 2.2″ 19″ / 1.4″
Total Winter Snowfall / Water Equiv. 54″ / 6.3” 91″ / 9.7″
Snowload in Valdez 10 lbs/sq. ft.

 

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 (12/6/2016) Depth Snow Water Equivalent
Milepost 2.5 Valdez  13.2″  2.3″
Milepost 18 15.4″ 2.1″
Milepost 29 Worthington Flats 32.2″ 6.4″
Milepost 37 Tsaina River bridge 24.1″ 4.1″
This survey is done the first week of each month beginning in December.

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:

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

Photo of Thompson Pass <here>

Map of Valdez Forecast areas and recreating zones <here> (Thank you Trevor Grams!)

Run map of some of the forecast area (2MB download)<here> (Thank you Sean Wisner)

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