Monday-Thursday 1/9-1/12

Issued: Mon, Jan 09, 2017 at 8AM

Expires: Thu, Jan 12, 2017

 

Strong wind moves snow further down onto lee slopes. Avoid features that look fat and smooth, especially gullies and steep unsupported slopes. Hard windslab is usually triggered at the thin rocky areas, or by heavy loads like multiple people or machines.

Hats off to those who can find the wind protected powder today.

Above 2,500ft Moderate

1,800 to 2,500ft Moderate

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

MONDAY TUESDAY WEDNESDAY & THURSDAY

DANGER SCALE

WIND SLAB:
Elevation: Above 1800′
Aspect: mostly south and west
Terrain: Near ridgelines, gullies and rollovers
Sensitivity: Stubborn
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Small
Danger Trend: Steady
Forecaster Confidence: Fair

PERSISTENT SLAB:
Elevation: 
Mostly above 2500′
Aspect: 
All
Terrain: 
Steep rocky slopes where facets exist under old and between windslab, especially interior of Thompson Pass
Sensitivity: 
Stubborn
Distribution: 
Specific
Likelihood (Human Triggered): 
Possible
Size: 
Large
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, Large, Very Large (size scale <here>)
Danger Trend: Increasing, Steady, Decreasing
Forecaster Confidence: Good, Fair, Poor

LIST OF AVALANCHE PROBLEMS <here>

SNOWPACK DISCUSSION: The extreme outflow wind event that started late Jan 5th had gusts to 94 mph on Thompson Pass and hit 64mph at the Valdez RWIS with stronger gusts reported else where in town.  A haze of airborne snow filled the skies as much of our soft snow sublimated into the atmosphere. Unfortunately for riders, our snowpack has been hit hard. The snow has thinned and been peeled back to rocks and old snow. Alders that were once laying down are popping back.

This thinning of our snowpack won’t do much for strengthening the structure. Expect lee (mostly south and west facing) terrain features (rollovers, ridges and gullies) to have wind slab. Sastrugi to knife hard was reported yesterday, hollow and squeaky.

VAC 20170106 Town Wind EventVAC 20170106 Wind Event

coastal-zone-iconMaritime (Coastal):
This zone is generally harboring a thicker snowpack in the upper elevations that has seen consistently warmer temperatures…especially the last few days. This combination has resulted in a stronger, more predictable snow structure. The most recent avalanche activity involved the newest, surface snow of the Dec.30-31st storm. If you can navigate your way through the lower elevation alder, soft snow can be found in wind protected alcoves.

intermountain-zone-iconInter-mountain (Transitional):
A large variance in depth and structure defines this zone’s snowpack structure. Weak, early season facets at the ground and between layers of windslab remain a concern, especially on steep, shallow and unsupported slopes. Many of the storms this season have not pushed interior very far, so inland of passes, the snow is generally thinner and more questionable. It has been colder on the interior side as well, preserving persistent weak layers. In the upper Tsaina Valley and north of Mile Post 36 along the highway corridor, the snow is reacting very similar to the continental region: weak, shallow structure that fails easily when loaded.

interior-zone-iconContinental (Interior):
More interior beyond Mile Post 46 and out past Billy Mitchell, the snowpack is thin and incredibly weak: mostly facets. Recent avalanches have stepped down to ground. This structure will not change until a significant storm rolls inland.

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

Recent Avalanche Activity

Due to cold temps and more than a week of wind driven snow, pockets of windslab over persistent weak layers is still the problem, similar to the older activity below.

coastal-zone-iconMaritime (Coastal):

  • Jan 6: Several loose dry & 1 wind slab size 1-2 avalanches out of steep rocks above 3000′.
  • Jan 6: Handful of wind slabs pulled off southerly aspects on a rocky Hogsback Ridge at MP 7 and at the hairpin below Moonlight and Odyssey.

VAC 20170106 Wind Slab S Odyssey

intermountain-zone-iconInter-Mountain (Transitional):  Avalanches inland of Thompson Pass proved there is still a dangerous buried weak layer (facets at the ground) that has a lower probability of triggering, but high consequence due to hard windslab to 2-3 feet overtop.

  • Jan 6: Two size 2 (D2) wind slabs released out of south-facing, windloaded, rocky pockets near ridgeline above Tsaina Valley on Three Stooges (MP 31)

VAC 20170106 3 Stooges above Tsaina

  • Jan 5 & Dec. 30: Wind loaded south face above Mile Post 37 near 3 Pigs: D2 slabs pulled out of steep and rocky terrain and immediately stepped down to ground

VAC 20170105 Natural Slabs 3 Pigs

  • Jan. 4: Three, size 2, south facing, slab avalanches seen looking up the Tsaina Valley: One failed on a broad face, mid slope, while the other two crowns were near a rocky, steep ridgeline.

interior-zone-iconContinental (Interior):

  • Dec. 30: D2 storm slab avalanche pulled out to ground mid south slope of Mt Tiekel over Mile Post 46

 

 

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  -15/ 30
Ridgetop Wind Forecast (direction/mph): NE/ 15-50
Snowfall (in):  0
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction 15 / NE 45 / NE
Max Wind Gust (mph) / Direction 30/ NE 70 / NE
Temperature Min / Max (*F) 33 / 45  -15/ 11

Weather Forecast: Omega Block of high pressure extends across much of Alaska, forecast to remain stationary for up to another week. While this is in place, outflow wind will continue northerly to 50mph in channeled terrain. Temperatures inland remain mostly well below zero F. In wind protected areas, an inversion is could develop again with warmer temps at upper elevations. Possible big dump this weekend.

Additional Info & Media

SNOW HISTORY: Valdez 1/8 AM Thompson Pass 1/9 AM
24 Hour Snow / Water Equiv. 0” /0.0” 0″ /0″
Storm Snow /Water Equiv. (12/30-12/31) 5” /0.68″ 18″ /1.6″
Current Snow Depth 26″ 15″ wind scoured
January Snow / Water Equiv. 0″ /0″ 0″ / 0″
Total Winter Snowfall / Water Equiv. 95.9″ / 8.16” 143″ / 14.4″
Snowload in Valdez 23 lbs/sq. ft.

img_20161228_130954img_20161228_130730

Photos of our new Nicks Valley Weather Station Python to the east, Berlin Wall to the west.

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 (1/3/2017) Depth Snow Water Equivalent
Milepost 2.5 Valdez  22.7″  4.7″
Milepost 18 27.9″ 5.9″
Milepost 29 Worthington Flats 44″ 9.9″
Milepost 37 Tsaina River bridge 33.8″ 5.6″
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:

  • coastal-zone-iconMaritime (Coastal) – from the Port of Valdez to Thompson Pass, all waters flowing into Valdez Arm and everything south of Marshall Pass.
  • intermountain-zone-iconInter-mountain (Transitional) – between Thompson Pass and Rendezvous Lodge.
  • interior-zone-iconContinental (Interior) – the dry north side of the Chugach (north of 46 Mile, including the Tonsina River).

Photo of Thompson Pass

 thompson-pass-ski-runs

Interactive Map of Valdez Forecast Areas w/ Many Resource Layers (Trevor Grams)

climate-zones-topoclimate-zones-satellitegoogle-earth1

Run Map of Thompson Pass Area (Sean Wisner) (2MB download)
VAC Run Map Thompson Pass

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.
Pete Carter

Forecaster: Pete Carter