Thursday-Sunday

Issued: Thu, Dec 01, 2016 at 8AM

Expires: Sun, Dec 04, 2016

Given that strong winds scoured our mountain snowscape early this week and left us with a variety of punchy and firm conditions, consider how this new snow is stacking up on and bonding with the old snow.

Travel conservatively until you can assess how the new snow is interacting with a variety of old surfaces (rocks, windslab and crusts) just beneath. Poor visibility will make wise terrain selection more challenging.

Lower elevations are filling in and specific features could build enough snow to move.

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

THURSDAY FRIDAY SATURDAY & SUNDAY
2-moderate

DANGER SCALE

STORM SNOW:

Elevation: 1800′ and above
Aspect: All
Terrain: Steep and lee features with drifting snow
Sensitivity: Responsive
Distribution: Widespread
Likelihood (Human Triggered): Likely
Size: Small to Medium
Danger Trend: Increasing
Forecaster Confidence: Good
Details: 5-8 inches of snow is accumulating and drifting with significant SE onshore winds.

PERSISTENT SLAB:

Elevation: 2500′ and above
Aspect: Mostly south and lee to outflow flow wind, but all suspect
Terrain: Ridgelines, rollovers, crossloaded features
Sensitivity: Stubborn
Distribution: Specific features
Likelihood (Human Triggered): Possible
Size: Small to Medium
Danger Trend: Increasing with new snow load
Forecaster Confidence: Fair
Details: North wind has loaded 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:
Not much terrain was left unscathed after 74mph  outflow winds stripped away and re-sculpted a good portion of our snowpack in the alpine. The snow was ripped down to ground, old facets, crust and windslab, but filled in other gullies….leveling out the landscape. Incredibly variable condition existed that were not the most enjoyable to recreate on….punching through up to the knee one minute and jaw chattering slab another. With 8 inches of new snow having fallen since then and more on its way…consider bonding of new snow to old old surfaces. Storm snow issues and drifting are of concern in addition to our persistent facets (seeing an increase in stress) that lay under some very firm slabs.

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

Isolated pockets of windslab, formed after our last storm event ending last weekend, popped off near ridgetops to size 1.5, mostly steep south and west aspects in the alpine.

Let us know if you see any new activity from this current storm.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 18/28
Ridgetop Wind Forecast (mph):  E-SE/15-30
Snowfall (in): 4-8″
WIND & TEMPERATURE Past 24 Hours: Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 6 / NE 30 / ESE
Max Wind Gust (mph) / Direction 19 / NE 20 / ESE
Temperature Min / Max (*F) 19 / 32 7 / 26

Light snow began yesterday afternoon, but increased around 5pm last night. 11 inches have accumulated in town and 5 inches at the upper elevations on Thompson Pass. The low pressure passing through the gulf has brought on warmer temperatures and SE onshore winds that will drop and shift as the low moves past us. Expect a couple more inches of snow in town and up to 8 more in the higher elevations by the time this precipitation dies down late tonight. Post storm conditions on Friday foresee strong NE, outflow winds and cooling temperatures as skies clear up this weekend.

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