Thursday-Sunday: New Year’s Day!!!!

Issued: Thu, Dec 29, 2016 at 8AM

Expires: Sun, Jan 01, 2017

As the last night’s storm snow gets transported on the lee side (variable due to changing wind direction) of terrain features, mind the thickening, newly formed soft slabs and think about about the run-out and consequences if something were to trigger and pull our a whole pocket of snow.

Expect natural activity to release out of steep and rocky terrain….limiting your time below these areas.

If a smaller avalanche is able steps down into the deep, persistent weak layer we are finding out there, the volume of snow and hazard will increase dramatically.

Above 2,500ft Considerable

1,800 to 2,500ft Considerable

Below 1,800ft Moderate

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

DANGER SCALE

STORM SNOW:
Elevation: All
Aspect: All
Terrain: Greater than 30* and in runouts of slopes above
Sensitivity: Touchy
Distribution: Widespread
Likelihood (Human Triggered): Likely
Size: Small to Medium
Danger Trend: Increasing
Forecaster Confidence: Good

PERSISTENT SLAB:
Elevation: Mostly above 2500′
Aspect: All
Terrain: Steep rocky slopes where facets exist under old windslab, especially interior of Thompson Pass
Sensitivity: Stubborn
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Medium
Danger Trend: Decreasing
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: 7 inches of new snow have blown in on Thompson Pass (5 in town) with southerly winds that quickly shifted to strong outflow winds from the NE. Touchy new soft slabs were already forming early in the storm Wednesday afternoon (see observations section) which have likely grown to 10-15 inch thick slabs today on varying slopes. This new load, combined with an additional 5-9 inches forecasted in the next 24 hours, will be resting precariously on weak surface grains and continue to stress test deeper weak layers in our snowpack.  

The most likely places for humans to trigger avalanches are windloaded gully walls and unsupported, steep rocky slopes. With a little more than two feet average snow depth at 2500′, our snowpack is still relatively thin in places with the depth and structure quite variable due to outflow wind events. In Nick’s Happy Valley, the new weather station relatively protected from wind, was recently reporting a snow depth of 52″.

Warmer temperatures on the coastal side of Thompson Pass has built a more uniform snowpack capped by a surface crust below ~3000′.

Above 3000′ and interior of the Pass has stayed cooler; preserving early season facets at the ground and between layers of windslab. The weak interface between these deep facets and firmer layers above have been failing and propagating very easily in areas (see observation from 12/28). It is not out of the picture for heavy loads such as a snowmachine or mulitple machines to trigger a steep, windloaded north facing slope and have it step down to persistent weak layers, increasing the avalanche size and destructive potential.

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

Recent Avalanche Activity

Dec. 28:

  • Natural D2 slab avalanche on N face of Berlin Wall
  • Natural D1 slab avalanche on S facing roll-over below Little Girls
  • Snowmachine Triggered Avalanche below Catchers Mitt in photo below: photo credit: Eric Christensen

Snowmachine Triggered Avalanche from Eric Christensen

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  7 / 26
Ridgetop Wind Forecast (mph): Var / 5-30
Snowfall (in):  5-9
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 5 / Var 22 / Var
Max Wind Gust (mph) / Direction 19/ E 43 / NE
Temperature Min / Max (*F) 27 / 31 9 / 24

Weather Forecast: Broken skies and cooling will change to warming and clouds as a Kamchatka low pushes a front upon us late tonight and into Friday afternoon. It could leave us with up to 9 inches of new by morning and possibly more to come on Friday. As winds have already shifted after last night’s storm, look for more of the same variable wind direction, but with strong outflows post Friday’s front with dropping temps.

Additional Info & Media

SNOW HISTORY: Valdez 12/29 AM Thompson Pass 12/29 AM
24 Hour Snow / Water Equiv. 4” /0.23” 7″ /0.7″
Storm Snow /Water Equiv. (12/28-12/29) 5” /0.32″ 7″ /0.7″
Current Snow Depth 30″ 34″
December Snow / Water Equiv. 72.5″ /4.01″ 60″ / 5.2″
Total Winter Snowfall / Water Equiv. 94.9″ / 8.07” 132″ / 13.5″
Snowload in Valdez 21 lbs/sq. ft.

img_20161228_130954img_20161228_130730

Photos of our new Nicks Valley Weather Station in the shadows of Python and the Berlin Wall.

SNOWFALL for LAST 24 HRS at OTHER STATIONS:
Nicks Valley at 4200 ft (in): 2″
Upper Tsaina at 1750 ft (in): ?”
Sugarloaf at 550 ft (in): 5″
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.

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