Thursday – Sunday

Issued: Thu, Dec 08, 2016 at 8AM

Expires: Sun, Dec 11, 2016

This last week left us with many natural and a handful of human/machine triggered avalanches in the mid and upper elevations on Thompson Pass.

Look, listen and feel for signs of firm, wind slab resting precariously on top of sugary snow grains (facets). This (strong on top of weak) layering can result in circumstances that are unpredictable and triggered from a distance….with dire consequences.

A variety of southerly facing aspects have been most problematic, but consider how the winds could vary and have loaded other slopes you are about to dabble on.

With 3-4 more inches of snow on the way, consider how it could mask old, firm surfaces or be the extra load that tips the balance.

 

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

THURSDAY FRIDAY SATURDAY & SUNDAY
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 features
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Steady
Forecaster Confidence: Fair
Details: Sustained north winds have built hard windslab over facets.

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:
Our last significant storm (Nov.30-Dec.1) with strong onshore (SE) winds left us with one to two feet of new snow throughout our region. It was quickly followed by a reversal to extreme outflow (NNE) winds which scoured and loaded many faces for days. These new slabs loaded up on top of mid-pack and basal facets in many areas.

Soon after (Dec.2-4th), many steep, cross-loaded, and top-loaded slopes were naturally and human triggered. A few of these avalanches stepped down to the old weak layers not far below. Both of the mid-pack and ground level faceted (sugar snow) layers have failed easily in tests, some collapsing at the ground.

Since then, an inch of new snow has been blown around and another 3-4 could arrive this evening with dominant NE winds.

20161202 Outflow winds at the gap

20161202 Outflow winds at the gap

 

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

Recent Avalanche Activity

  • Windslabs sitting on weak facets have recently released naturally and by skiers/machines. Please share pics and locations if you find new activity.
20161204 North Odyssey Wind Slab Triggered by Snow Machine

20161204 North Odyssey Wind Slab Triggered by Snow Machine

 

20161203 Bald Boy & Adjacent Sympathetic

20161203 Triggered from below

20161203 Triggered from below: Odyssey Lake

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  -3/17
Ridgetop Wind Forecast (mph):  25-50/ NE
Snowfall (in):  3-4
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 17 / NE 42 / NE
Max Wind Gust (mph) / Direction 21 / NE 54 / NE
Temperature Min / Max (*F) 14 / 19 -5 / -1

A weak weather front has moved in, bringing clouds and ever so slightly warmer temperatures. It could drop up to 4 inches of precipitation this afternoon and evening before starting to clear and cool again Friday. Outflow winds will continue to dominate from the northeast throughout.

Additional Info & Media

SNOW HISTORY: Valdez 12/8 AM Thompson Pass 12/8AM
24 Hour Snow / Water Equiv.  0” /0″ 0″ /0″
Storm Snow /Water Equiv. (12/6-12/7) 3.5” /0.2″ 1″ /0.1″
Current Snow Depth 18.3″ 18″
December Snow / Water Equiv. 23.5″ / 1.7″ 17″ / 1.3″
Total Winter Snowfall / Water Equiv. 45.5″ / 5.8” 89″ / 9.6″
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.

Forecaster: Kevin Salys