Christmas Eve – Tuesday

Issued: Sat, Dec 24, 2016 at 8AM

Expires: Tue, Dec 27, 2016

Multiple avalanches were reported yesterday! Both natural and snowmachine triggered slides were reported to release down to the ground yesterday which continue to advertise our regional deep snow (up to 4′ deep) instabilities.

These have been accompanied by extensive settlement/whumphing the last week….sometimes supportive enough to not occur on the first passing.

Respect the unpredictable nature of this problem and choose terrain appropriately as these avalanches be triggered in shallow edges of the firm slab….especially in unsupported terrain.

As you look for a shifting of winds to the ESE, mind new, sensitive wind slab formation on terrain features loading with drifting snow.

 

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

SATURDAY SUNDAY MONDAY & TUESDAY

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: 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:
Current NE winds and soon to arrive ESE winds will affect our recently fallen 2+ feet of snow that has accumulated in our region the last week. Look for new wind slab formation on lee aspects in wind exposed areas. Given the variable winds, a variety of aspects could be suspect.

Recent avalanche activity demonstrates the continued issues 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 slopes leeward of previous NE winds. Recent snow test results have been completely variable and dependent on the depth of the snowpack. Shallow areas less than a 3 feet were dramatically weaker, 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 when choosing terrain.

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

Recent Avalanche Activity

  • Fri Dec 23: Bro Bowl: Snowmachine triggered very thick hard slab in steep terrain
  • Fri Dec 23: Mile Post 37: Multiple southerly slopes loaded by N winds; natural wind slab release stepping down to persistent weakness at ground
  • Thur Thur Dec 22: Small dry loose sluffs in rocky and steep terrain
  • Thur Dec 22: Below the NE ridge of 27 Mile Peak: D2 storm slab release? N aspect above the Worthington Glacier seen from Little Girls.
  • Many signs of instability continue to be seen and felt by skiers and riders over the last week in a variety of areas: cracking, whumphing, and collapsing

 

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  17 / 27
Ridgetop Wind Forecast (mph): Var/ 10-20
Snowfall (in):  3-4
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 9/NE 25/NE
Max Wind Gust (mph) / Direction 20/NE 34/NE
Temperature Min / Max (*F) 23 /28 5 / 11

Weather Forecast: As a low moves east and swings a front at us more from the east, variable, moderate winds will arrive with snowfall and warming temperatures this afternoon. Up to 5 inches of precipitation could fall by Monday morning when it will dissipate even though clouds could linger through Tuesday. Expect dropping temps, clearing skies, and a return of strong outflow winds post storm.

Additional Info & Media

SNOW HISTORY: Valdez 12/24 AM Thompson Pass 12/21 AM
24 Hour Snow / Water Equiv. Trace” /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): 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