Thursday – Sunday

Issued: Thu, Dec 22, 2016 at 8AM

Expires: Sun, Dec 25, 2016

While storm snow concerns (loose snow and soft slabs) and increasing winds out of the NE affect the upper layers of our snowpack, red flags continue to fly high all throughout our region advertising deeper snow instabilities.

A concerning, persistent, weak layer topped by firmer hard slabs is buried up to 4′ below the surface. High consequence slab avalanches could be directly triggered by humans or by smaller surface snow movement 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

THURSDAY FRIDAY SATURDAY & SUNDAY
3-considerable

DANGER SCALE

STORM SNOW:

Elevation: All
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:
Snow has continued to fall and accumulate bit by bit (over 2 feet) throughout our region the last week. While more has fallen in the port/maritime zone, a significant amount of snow has softened surfaces up on Thompson Pass and the interior. In higher, more wind exposed areas, more drifting and slab formation has occurred.

Evaluation up near 4000ft on Thompson Pass yesterday demonstrated some weak interfaces between storm layers, but propagation was variable: depending on slope, aspect and drifting.

The continued concerning problems is the widespread finding of buried facets (sugar snow) deep in our snowpack with very firm slabs overlying them. The firm slabs on top have varied thicknesses up to 4ft, largely affected by wind drifting snow onto leeward slopes. As settlement and whumping is continuously felt by the weight of skiers throughout the region, consider the dramatic change in load introduced by snowmachines.

Triggering failure in this faceted weak layer near the ground in steep, rocky and unsupported terrain could result in the whole snowpack releasing off the montain side. The challenging and unpredictable nature of this snow problem necessitate conservative terrain selection until the area is well assessed.

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

Recent Avalanche Activity

  • No new avalanche activity seen.
  • Many signs of instability continue to be seen and felt by skiers and riders up to yesterday in a variety of areas: cracking, whumphing, and collapsing: 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):  10 / 20
Ridgetop Wind Forecast (mph): NE / 10-40
Snowfall (in):  Trace
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 3/NE 19/NE
Max Wind Gust (mph) / Direction 15/NE 29/NE
Temperature Min / Max (*F) 27 /34 10 / 24

Weather Forecast: Scattered flurries could fall from the heavens today, but the general trend will be clearing and cooling: teens in town and down near zero on Thompson Pass.  Come Saturday, clouds will start to build again preceding a bit of precipitation Sunday with another low moving in. Expect strong outflow winds over the passes until the next front moves in on Saturday.

Additional Info & Media

SNOW HISTORY: Valdez 12/22 AM Thompson Pass 12/21 AM
24 Hour Snow / Water Equiv. 1” /0.06″ 4″ /0.4″
Storm Snow /Water Equiv. (12/20-22) 13.5” /0.79″ 12″ /1.2″
Current Snow Depth 34.25″ 27″
December Snow / Water Equiv. 64.3″ /3.71″ 44″ / 3.7″
Total Winter Snowfall / Water Equiv. 86.7″ / 7.76” 116″ / 12″
Snowload in Valdez 19 lbs/sq. ft.

 

SNOWFALL for LAST 24 HRS at OTHER STATIONS:
Nicks Valley at 4200 ft (in): ?”
Upper Tsaina at 1750 ft (in): 1?”
Sugarloaf at 550 ft (in): 3″
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