Tuesday-Friday 2/13-2/16

Issued: Tue, Feb 13, 2018 at 8AM

Expires: Fri, Feb 16, 2018

Expect both naturally releasing and human triggered windslab avalanches today

Above 2,500ft Considerable

1,800 to 2,500ft Considerable

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

Tuesday Wednesday Thursday
& Friday

DANGER SCALE

 

STORM SNOW:
Elevation:
    Above 1500′
Aspect:  
  All
Terrain: 
   >35 degrees
Sensitivity:
    Responsive
Distribution:
    Widespread
Likelihood (Human Triggered):
   Possible
Size:   
Small – Large
Danger Trend:   Decreasing
Forecaster Confidence:
   Good

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

PERSISTENT SLAB:
Elevation:
   Above 2500′
Aspect:
   All
Terrain: 
  35+ degrees steepness
Sensitivity:
   Stubborn
Distribution:   
Specific
Likelihood (Human Triggered):   
Possible
Size:   
Small – 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 Monday January 12 storm brought at least two feet of snow to the maritime snow climate zone south of the Port. Much less snow accumulated in the continental snow climate zone north of Serendipity at Milepost 46. A foot of snow fell in the inter-mountain snow climate zone north of Thompson Pass.

The cold, clear weather of the past month between the 1/15 and 2/13 storms created a weak layer over the old snow and a poor bond for the new storm snow to adhere to. Furthermore, the old snow is a good, smooth bed surface. Expect easy shear results at the interface of the old snow with the new snow. Strong north winds will create new windslabs Tuesday, triggering avalanches.

Recent Avalanche Activity

February 13: numerous windslab releases to size D2 triggered from moderate to strong northerly outflow winds, particularly on cross loaded features.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  20 / 29
Ridgetop Wind Forecast (direction/mph): NE / 40-60
Snowfall (in): 0”
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction   ~ / ~  10 / NE&SE
Max Wind Gust (mph) / Direction  ~ / ~  30 / NE
Temperature Min / Max (*F)  26 / 31  17 / 31

Weather Forecast:     Sunny Tuesday and Wednesday with northerly outflow winds gusting to 60 mph over wind exposed terrain and low temperatures in the teens. Clouds returning Wednesday with a chance of snow. More sun Thursday into the weekend with low temperatures in the single digits.

Additional Info & Media

SNOW HISTORY: Valdez 2/13 AM Thompson Pass 2/13 AM
24 Hour Snow / Water Equiv. 6”/ 0.5″ 8″ / 0″
Storm Snow /Water Equiv. (2/12) 16” / 1.5″ 12″ / 1.5″
Current Snow Depth 37″ 84″
February Snow / Water Equiv. 17.5″ / 1.5″ 15″ / 1.7″
Total Winter Snowfall / Water Equiv. 95″ / 23.55” 315″ / 32″
Snowload in Valdez 45 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS / STORM TOTAL (Feb. 12) / STORM WATER EQUIV.:
Nicks Valley at 4200 ft (in): ” / ” / “
Upper Tsaina at 1750 ft (in): ” / ” / “
Sugarloaf at 550 ft (in): ” / ” / “
SNOW DEPTH & WATER SURVEY (2/5/2018) Depth Snow Water Equivalent
Milepost 2.5 Valdez  22″  7.6″
Milepost 18 32.5″ 9.6″
Milepost 29 Worthington Flats 62″ 19.4″
Milepost 37 Tsaina River bridge 52.6″ 16.4″
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.
Pete Carter

Forecaster: Pete Carter