Friday – Monday

Issued: Fri, Dec 23, 2016 at 8AM

Expires: Mon, Dec 26, 2016

As strong NE winds continue, mind new, sensitive wind slab formation on terrain features loading with drifting snow.

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 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

FRIDAY SATURDAY SUNDAY & MONDAY

DANGER SCALE

WIND SLAB:

Elevation: 1800′ and above
Aspect: Lee to prominant wind
Terrain: Near ridges, rollovers and loaded features
Sensitivity: Responsive
Distribution: Widespread
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Increasing w cotinued strong wind from NE
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:
An uptick in wind out of the NE is has been moving our snow (over 2 feet) that has accumulated in our region the last week. Look for new wind slab formation on lee aspects in wind exposed areas. Winds seems to be more severe channeling over the passes than up higher on ridges and peaks.

Evaluation up around 4000ft on Thompson Pass the last couple days demonstrate that many of the weak storm interfaces have been resistant to propagation.

The more concerning problem 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. The results were completely variable and dependent on the depth of the snowpack. Shallow areas less than a 3 feet were dramatically weaker and sensitive and failing very easily in tests. On the contrast, a very deep wind loaded area had very solid structure and was moist and glued to the ground.

As settlement and whumping is continuously felt by the weight of skiers throughout the region, consider the dramatic change in load introduced by snowmachines.

The question remains: How easily it is to trigger these deep weaknesses from shallow areas nearby?

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

Recent Avalanche Activity

  • Small dry loose sluffs in rocky and steep terrain
  • D2 storm slab? release below the NE ridge of 27 Mile Peak. N aspect above the Worthington Glacier seen from Little Girls.
  • 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.

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):  0
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 8/NE 32/NE
Max Wind Gust (mph) / Direction 20/ENE 39/NE
Temperature Min / Max (*F) 26 /32 10 / 14

Weather Forecast: An upper level trough brought us a dusting of snow in town and about an inch up on Thompson Pass. Winds could back down slightly today and temps and clouds increase tonight as a front moves in. Extensive moisture, a shift of winds to the SE should hit us Saturday afternoon-evening. Weather will persist into Monday night and a half of foot of snow could accumulate through the duration.

Additional Info & Media

SNOW HISTORY: Valdez 12/24 AM Thompson Pass 12/21 AM
24 Hour Snow / Water Equiv. 0Trace” /0.01″ 4″ /0.4″
Storm Snow /Water Equiv. (12/20-22) 13.5” /0.79″ 12″ /1.2″
Current Snow Depth 28.3″ 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): 1″
Upper Tsaina at 1750 ft (in): 1″
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