Wednesday-Saturday 2/21-24

Issued: Wed, Feb 21, 2018 at 8AM

Expires: Sat, Feb 24, 2018

Above 2,500ft Moderate

1,800 to 2,500ft Low

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

Wednesday Thursday Friday
& Saturday

DANGER SCALE

 

WIND SLAB:
Elevation:   Above 2000′
Aspect:   Lee of ridges, gullies, ridgetops
Terrain:   Upper elevation terrain exposed to wind
Sensitivity:   Stubborn until Friday, then Touchy-Responsive
Distribution:   Specific
Likelihood (Human Triggered):    Possible, (elevating to Likely on Friday)
Size:   Small – Large
Danger Trend:   Decreasing (Increasing Friday)
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:
   Decreasing
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:     Expect new windslabs Friday.

The Feb. 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 within the inter-mountian 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 Tuesday Feb 13 created new windslabs triggering numerous relatively small avalanches, size D2, on mostly cross-loaded slopes.  Moderate winds continue to transport snow in the upper elevations.

Our persistent slab concern still exists and our test pits indicate that this layer is buried 2-6′ (60-180cm) beneath the surface.  This layer is stubborn to trigger, but due to depth, will carry larger consequences.  We’re still tracking the distribution but suspect it could still be widespread, especially above 2500′.  This layer will be easier to trigger near rocky outcrops and where snowpack is generally thinner.

Recent Avalanche Activity

No new observations.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  0 / 25
Ridgetop Wind Forecast (direction/mph): light/variable
Snowfall (in):  0”
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction   5 / NE   25 / NE
Max Wind Gust (mph) / Direction  15 / NE  45 / NE
Temperature Min / Max (*F)  27 / 40  5 / 25

Weather Forecast:     Cloudy Wednesday. Good chance of 2-3 inches of snow Thursday.  Sunny Friday and Saturday. Strong winds to hurricane force and blowing snow Friday. Chance of one inch of snow Sunday.

Additional Info & Media

SNOW HISTORY: Valdez 2/21 AM Thompson Pass 2/21 AM
24 Hour Snow / Water Equiv. 0”/ 0″ 0″ / 0″
Storm Snow /Water Equiv. (2/12) 16” / 1.5″ 12″ / 1.5″
Current Snow Depth 35″ 77″
February Snow / Water Equiv. 19.6″ / 1.61″ 17″ / 1.8″
Total Winter Snowfall / Water Equiv. 97.74″ / 23.65” 307″ / 32.1″
Snowload in Valdez 52 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