Friday-Monday

Issued: Fri, Dec 02, 2016 at 8AM

Expires: Mon, Dec 05, 2016

Get out and enjoy the snow before it blows away or gets compacted into sastrugi or wind board.

Onshore winds and a foot of new snow on Thompson Pass have filled in the landscape, masking undulating, firm surfaces just beneath. Get out on non-consequential features and evaluate how the new snow is bonding with old sugar snow and in between storm layers before moving into steeper terrain.

Lower elevations are filling in and specific features could build enough snow to move, especially with strong winds moving snow around this weekend.

It still is early season: Early season dangers explained here (link to summary by Avalanche Canada).

Above 2,500ft Considerable

1,800 to 2,500ft Considerable

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

GENERAL DANGER RATING OUTLOOK

FRIDAY SATURDAY SUNDAY & MONDAY
2-moderate

DANGER SCALE

STORM SNOW:

Elevation: 1800′ and above
Aspect: All
Terrain: Steep and onshore wind lee features with drifting snow
Sensitivity: Responsive
Distribution: Widespread
Likelihood (Human Triggered): Likely
Size: Small to Medium
Danger Trend: Increasing
Forecaster Confidence: Good
Details: 12 inches of snow has accumulated and drifted with significant SE onshore winds.

WIND & PERSISTENT SLAB:

Elevation: 2500′ and above
Aspect: Mostly south and lee to outflow flow wind, but all suspect
Terrain: Ridgelines, rollovers, crossloaded features
Sensitivity: Responsive
Distribution: Specific features
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Increasing with offshore blowing snow
Forecaster Confidence: Fair
Details: North wind will creat new slabs and add weight and stress on persistent facets (sugar snow) lower in the snowpack.

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 foot of new snow (scoured to nothing or drifted to 2+ feet in places) on Thompson Pass and more in the maritime near town is settling in on top of a variety of surfaces: ground, old facets, crust and windslab. The warm storm seems to have allowed the new snow to stick fairly well to these surfaces, but continue to monitor this, especially at higher, colder elevations. Strong onshore winds during the storm have created sensitive interfaces of soft slab that would fail in compression, but didn’t want to support propagation. As northerly, outflow winds return, look for intense snow transport and sensitive new wind slab formation. These will be responsive to human interaction. Lastly, don’t forget about our deeper, persistent facets that lay under some very firm slabs. Give these guys due respect as stress and mass increase on top of them.

20161123: Wind Slab on facets!!!! ECTP3 Q1 SC on 1mm NSF

20161123: Older demo of  Wind Slab problems on facets!!!! ECTP3 Q1 SC on 1mm NSF

Find more photos and observations below: at the bottom of the page. Sharing your observations helps others make informed decisions about where and how to go.

Recent Avalanche Activity

 

No new avalanche activity observed.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 9/21
Ridgetop Wind Forecast (mph):  NE/15-45
Snowfall (in): Trace
WIND & TEMPERATURE Past 24 Hours: Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 0? 27 / SE
Max Wind Gust (mph) / Direction ? 38 / NE
Temperature Min / Max (*F) 29 / 32 13 / 29

As a high pressure system returns to the area through the weekend, clear skies, cold temperatures and gusty winds will dominate. Cold air in the interior and a low in the gulf will create temperatures from the single digits to below zero and 50+ mph offshore winds through the passes. Early next week, winds will back and down and clouds and temperatures increase.

Additional Info & Media

SNOW HISTORY: Valdez 12/1 AM Thompson Pass 12/1 AM
Current Snow Depth 23″ 27″
24 Hour Snow / Water Equiv. 11” /0.6″ 8″ /0.5″
Storm Snow /Water Equiv. (11/30-12/2?) 11” /0.6″ 8″ /0.5″
November Snow / Water Equiv. 33.3″ / 4.7″ 57″ / 6.4″
Total Winter Snowfall / Water Equiv. 33.3″ / 4.7” 80″ / 8.8″
Snowload in Valdez 5.0 lbs/sq. ft.
SNOW DEPTH & WATER SURVEY (date) Depth Snow Water Equivalent
Milepost 2.5 Valdez  ?″  ?″
Milepost 18 ?″ ?″
Milepost 29 Worthington Flats ?″ ?″
Milepost 37 Tsaina River bridge ?″ ?″
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 <here>

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