Christmas Day – Wednesday

Issued: Sun, Dec 25, 2016 at 8AM

Expires: Wed, Dec 28, 2016

 

Santa brought four inches fresh Christmas snow to Thompson Pass.  Warm southeast wind is building heavier windslab over colder, dry snow. The wind direction will shift to northeast, creating potential for rollovers and unsupported slopes on all aspects to be sensitive to human trigger.

Poor visibilty will make it difficult to see hazards.

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

SUNDAY MONDAY TUESDAY & WEDNESDAY

DANGER SCALE

WIND SLAB:

Elevation: 1800′ and above
Aspect: All aspects due to wind shifting from southeast to north Sunday
Terrain: Near ridges, rollovers and loaded features
Sensitivity: Responsive
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Increasing
Forecaster Confidence: Fair

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: 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: A few more inches of warmer snow will be transported by southeast wind today. Expect fresh windslab 6″ to a foot deep over colder settled snow from Dec.20-22 to be possible for humans to trigger.

Windslab avalanches have the possbility to step down to deeper persistent weak layers, increasing their size and destructive potential.

The variability of depth and structure due to the outflow wind events and cold temperatures so far this season create a lot of uncertainty about our snowpack’s stability. Choose conservative routes, avoiding terrain traps.

The portside snowpack is generally more uniform and stronger than interior of Mile 35.

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 above MP 29: Snowmachine and rider triggered hard slab in steeps near rockbands, northeast aspect, ~4500′
  • Fri Dec 23   Mile Post 37: A few southerly slopes 3500-4500′ loaded by north wind released naturally, windslab & storm snow to size 2
  • 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, north 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):  22 / 28
Ridgetop Wind Forecast (mph): NE/ 10-30
Snowfall (in):  4-8
WIND & TEMPERATURE
past 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 5/ENE 20/SE
Max Wind Gust (mph) / Direction 15/ENE 30/SE
Temperature Min / Max (*F) 22 /28 7 / 25

Weather Forecast: Warming trend Christmas Day with snow accumulation 4-8 inches through Monday night. Southeast wind shifting northeast wind to 30mph, keeping temperatures cooler with less snowfall north of Thompson Pass.

Additional Info & Media

SNOW HISTORY: Valdez 12/26 AM Thompson Pass 12/26 AM
24 Hour Snow / Water Equiv. Trace” /0.01″ 2″ /0.2″
Storm Snow /Water Equiv. (12/24-26) 3” /0.79″ 6″ /0.6″
Current Snow Depth 30″ 26″
December Snow / Water Equiv. 67.3″ /3.71″ 51″ / 4.4″
Total Winter Snowfall / Water Equiv. 89.7″ / 7.76” 123″ / 12.7″
Snowload in Valdez 21 lbs/sq. ft.

 

SNOWFALL for LAST 24 HRS at OTHER STATIONS:
Nicks Valley at 4200 ft (in): 3″
Upper Tsaina at 1750 ft (in): 0.1″
Sugarloaf at 550 ft (in): trace”
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.
Sarah Carter

Forecaster: Sarah Carter