Sunday-Wednesday 1/14-1/17

Issued: Sun, Jan 14, 2018 at 8AM

Expires: Wed, Jan 17, 2018

Avalanche danger increasing with rising temperature and continued snow and rain. Stay out from underneath large avalanche paths.

Above 2,500ft Considerable

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

SUNDAY MONDAY TUESDAY & WEDNESDAY

DANGER SCALE

 

 

WIND SLAB:
Elevation:
   Above 2000′
Aspect:  
 Lee of ridges, gullies, ridgetops
Terrain: 
  All terrain exposed to wind
Sensitivity:
   Responsive
Distribution:   
Specific
Likelihood (Human Triggered):   
Likely
Size:   
Small – Large
Danger Trend:
   Increasing 
Forecaster Confidence:
   Fair

STORM SLAB:
Elevation:
   Above 1800′
Aspect:
   All
Terrain: 
  35+ degrees steepness
Sensitivity:
   Responsive
Distribution:   
Widespread
Likelihood (Human Triggered):   
Possible
Size:   
Small – Large
Danger Trend:
   Increasing 
Forecaster Confidence:
   Fair

PERSISTENT SLAB:
Elevation:
   Above 2500′
Aspect:
   All
Terrain: 
  35+ degrees steepness
Sensitivity:
   Stubborn
Distribution:   
Specific
Likelihood (Human Triggered):   
Possible
Size:   
Small – Large
Danger Trend:
   Increasing 
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: This new, warm storm front moved in Saturday afternoon and has dropped a foot (30cm) of stormsnow with 1/2″ (14mm) water equivalent at Thompson Pass so far. 10″ at 46 Mile. The temperature rose rapidly in the last 24 hours, with the freezing line now at about 1900′. With another foot possible through tomorrow morning, a storm slab is forming.

This new snow was being moved at ridgetops overnight by moderate southeast wind, and as of  6am this morning, shifted to the northeast.

The new storm and windslabs are laying in over a weak layer of buried late December NSF facets <info here> and surface hoar.  The concern is that where this persistent weak layer still exists, and is reactive, the stress of the new stormsnow may tip the balance and release slabs more than 18″ (45cm) deep. Expect human triggered avalanches possible near ridgetops and rollovers.

Last weekend (Jan.7): above Milepost 35, riders where feeling significant whumps. Snowpack tests consistently produced easy shear results two feet from the snowpack surface running on the Dec. 26 surface hoar. The question is: what is the distribution of this weak layer and will it be reactive with this new load?

Three to five feet of storm snow has fallen since Jan 1. During the January 1-3 storm strong southerly winds drifted windslabs to waist deep at Thompson Pass. Strong northerly outflow winds to 60mph January 4-9 have built pencil hard windslabs on exposed slopes.

On behalf of the snow sports community, thank you for sharing your observations!

Recent Avalanche Activity

A few windslab avalanches to size D2 where observed along the highway corridor over Thompson Pass between Mileposts 23 and 28 Tuesday January 9.  No additional reports of avalanches since then.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  30/ 35
Ridgetop Wind Forecast (direction/mph): NE / 6-20
Snowfall (in): 9-22
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction   5 / SE-N  22 / SE-NNE
Max Wind Gust (mph) / Direction  16 / NNE  36 / ENE
Temperature Min / Max (*F)  29 / 42  9 / 34

Weather Forecast:   Today, rain below 1800′, snow above, heavy at times. Models show the possibility of 9-22″ more snow expected in the alpine in next 24 hours with 2.5″ water equivalent possible through Tuesday morning. Freezing line rising to near Thompson Pass. Moderate NE ridgetop wind. This storm will slow down in intensity Tuesday, reducing to showers and flurries. with

Additional Info & Media

SNOW HISTORY: Valdez 1/14 AM Thompson Pass 1/14 AM
24 Hour Snow / Water Equiv. 0.45”/ 0.45″ 12″ / 0.45″
Storm Snow /Water Equiv. (1/13-present) rain” / 0.45″ 12″ / 0.45″
Current Snow Depth 25″ 78″
January Snow / Water Equiv. 13.25″ / 4.19 ″ 44″ / 3.55″
Total Winter Snowfall / Water Equiv. 77.1″ / 20.49” 252″ / 27.75″
Snowload in Valdez 45 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS / STORM TOTAL / STORM WATER EQUIV.:
Nicks Valley at 4200 ft (in): 8″ / 8″ / ~”
Upper Tsaina at 1750 ft (in): 6″ / 6″ / 0.5″
Sugarloaf at 550 ft (in): rain” /rain” / 0.4″
SNOW DEPTH & WATER SURVEY (2/1/2017) 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.

Weather Quicklinks:

 

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 Continental Forecasts, Intermountain Forecasts, Maritime Forecasts.
Sarah Carter

Forecaster: Sarah Carter