MLK-Thursday 1/16-1/19

Issued: Mon, Jan 16, 2017 at 8AM

Expires: Thu, Jan 19, 2017

DANGEROUS AVALANCHE CONDITIONS

Travel in avalanche terrain is not recommended. Strong northeast wind near ridgetops and passes is moving more than 3 feet of new storm snow.

Above 2,500ft High

1,800 to 2,500ft High

Below 1,800ft Considerable

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: South – West
Terrain:
Slopes steeper than 30 degrees, top and crossloaded by NE wind
Sensitivity: 
Touchy
Distribution:
 
Specific
Likelihood (Human Triggered): 
Nearly certain
Size: 
Small – Large
Danger Trend: 
Increasing with continued strong wind
Forecaster Confidence: 
Good

STORM SNOW:
Elevation: All
Aspect: 
All
Terrain:
Slopes steeper than 30 degrees, especially where new storm snow fell on hard surfaces.
Sensitivity: 
Touchy
Distribution:
 Widespread
Likelihood (Human Triggered): 
Very Likely
Size: 
Small – Large
Danger Trend: 
Increasing 
Forecaster Confidence: 
Good

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: 
Small – Large
Danger Trend: 
Increasing with extra snow load 
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: Classic storm snow avalanche conditions: in the last 4 days we have had two back to back storms that dropped more than 3 feet of snow with nearly 4 inches water equivalent at Thompson Pass.  Temperatures initially were cool. Saturday warmed up with rain/snow mix below 2000′. Now temps are cooling and a up to a foot more snow is possible before it quits Tuesday.

Northeast wind picked up at Thompson Pass early Saturday morning and is continuing to cause intense snow transport with thigh deep drifts reported.

There is instability both within storm snow layers and on the bed surfaces it fell on. Where the storm snow and new windslab has not bonded to the hard windboard (built by January 6th north wind event), natural avalanches are likely with human triggered avalanches nearly certain. Staying off and out from under steep terrain until the snowpack has time to adjust is recommended.

Interior of Thompson Pass the snowpack was weak and thin before the storm. The new weight will stress old persistent weak layers either naturally triggering avalanches or setting up a situation prime for human trigger after the storm.

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

Recent Avalanche Activity

Poor visibility prevented new avalanche obs.

coastal-zone-iconMaritime (Coastal):

  • Reports Sunday of possibly hearing avalanche activity near East Peak.

intermountain-zone-iconInter-Mountain (Transitional):  Poor visibility did not allow for observations. The January 6 extreme wind event triggered numerous avalanches inland of Thompson Pass many releasing to ground, again reminding us of the dangers of the buried weakness of sugar snow (facets) at the ground) now covered with 2-3 feet thick hard windslab.

interior-zone-iconContinental (Interior):

  • Poor visibility limited new observations. Storm slab avalanches suspected, capable of stepping down into deeper persistent layers.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  8/25
Ridgetop Wind Forecast (mph/direction): 10-40/NE
Snowfall (in):  6-12″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  7/W  35/NE
Max Wind Gust (mph) / Direction  24/W  46/NE
Temperature Min / Max (*F)  30/35  12/20

Weather Forecast: Snow will continue today, heavy at times after 10am with acculumation up to an additional foot. Northeast wind to 40mph through passes and channeled terrain. Cooling trend, with single digits F in town by the time the snow abates Tuesday. Clear skies return Wednesday.

Additional Info & Media

SNOW HISTORY: Valdez 1/16 AM Thompson Pass 1/16 AM
24 Hour Snow / Water Equiv. 4.3” /0.34” 10″ /1″
Storm Snow /Water Equiv. (1/12-1/16) 20” settled stormsnow + rain/3.5″ 45″ /3.7″
Current Snow Depth 40″ 37″ (wind scoured)
January Snow / Water Equiv. 42.6″ /3.5″ 45″ / 3.7″
Total Winter Snowfall / Water Equiv. 104.5″ / 16.31” 188″ / 18.1″
Snowload in Valdez 40 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): ~5″
Upper Tsaina at 1750 ft (in): ~3″
Sugarloaf at 550 ft (in): ~3″
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.
Sarah Carter

Forecaster: Sarah Carter