Wednesday – Saturday

Issued: Wed, Dec 21, 2016 at 8AM

Expires: Sat, Dec 24, 2016

There is a persistent weak layer buried 2-4′ deep in start zones. Above 2000′ humans are likely to trigger slab avalanches on steep slopes near rocks, under cliffs, and on thin edges of windslab.

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

WEDNESDAY THURSDAY FRIDAY & SATURDAY
3-considerable 3-considerable

DANGER SCALE

STORM SNOW:

Elevation: Above 2000′ elevation
Aspect: All
Terrain: Primarily steeper than 35 degrees
Sensitivity: Responsive
Distribution: Widespread
Likelihood (Human Triggered): Likely
Size: Small to Medium
Danger Trend: Steady
Forecaster Confidence: Fair

PERSISTENT SLAB:

Elevation: Mostly above 2500′
Aspect: All
Terrain: Steep rocky slopes where facets exist under old windslab
Sensitivity: Stubborn
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Steady
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:  Since Saturday December 17, more than two feet of new snow has accumulated. The new snow is stiffening into a soft slab and is wind drifted in exposed areas. Tuesday many whumphs and collapses were felt by backcountry travelers; this failure is in facets to 3mm near the bottom of our snowpack.

On 12/17 a deep hard slab natural avalanche was observed on the northwest aspect above the main gully of North Odyssey above Milepost 27.5, reinforcing the concern the sugar snow (facets) on the ground have the potential to release the entire season’s snowpack.

  • December 17th: Snowmachines caused cracking down to the persistent weak layer, old facets buried by December’s snowfalls.

kyle-stormslab-crack-20161217

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

Recent Avalanche Activity

  • Flat light and cloud has limited avalanche observations in the upper elevations.
  • Signs of instability were seen and felt by skiers and riders December 18, 19 & 20: cracking, whumphing, and collapsing throughout Thompson Pass area. Scroll down below the forecast to view observation submissions.
  • December 17th a natural avalanche was spotted in the main gully of North Odyssey that released to the ground.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  16 / 25
Ridgetop Wind Forecast (mph): E / 5-20
Snowfall (in):  3-4
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 0 S – E / 15
Max Wind Gust (mph) / Direction 0 ESE / 22
Temperature Min / Max (*F) 25 /32 19 / 25

Weather Forecast: Flurries with additonal accumulation for 1-4″ as this low pressure system passes. Slight cooling trend as skies clear this afternoon. East wind to 20 mph in passes and at ridgetops, swinging to north wind.

Additional Info & Media

SNOW HISTORY: Valdez 12/21 AM Thompson Pass 12/21 AM
24 Hour Snow / Water Equiv. 3.5” /0.73″ 4″ /0.4″
Storm Snow /Water Equiv. (12/20-21) 12.5” /0.73″ 12″ /1.2″
Current Snow Depth 33.46″ 27″
December Snow / Water Equiv. 63.3″ /3.6″ 44″ / 3.7″
Total Winter Snowfall / Water Equiv. 85.7″ / 7.7” 116″ / 12″
Snowload in Valdez 19 lbs/sq. ft.

 

SNOWFALL for LAST 24 HRS at OTHER STATIONS:
Nicks Valley at 4200 ft (in): Tr”
Upper Tsaina at 1750 ft (in): Tr”
Sugarloaf at 550 ft (in): ?”
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.
Pete Carter

Forecaster: Pete Carter