Wednesday-Saturday 3/21-3/24

Issued: Wed, Mar 21, 2018 at 8AM

Expires: Sat, Mar 24, 2018

Above 2,500ft Considerable

1,800 to 2,500ft Considerable

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 1000′
Aspect:   Lee of ridges, gullies, ridgetops
Terrain:   All terrain exposed to northerly winds
Sensitivity:   Responsive
Distribution:   Specific
Likelihood (Human Triggered):   Likely
Size:   Small – Large
Danger Trend:   Steady
Forecaster Confidence:    Good

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:     Winds gusting over 100 mph continue to move a lot of snow producing numerous, mostly smaller avalanches with crown fracture lines, and even deposits, quickly filled in with subsequent drifted snow. A great quantity of eroded snow simply disappears with high winds and low relative humidity. Once the old snow is eroded, it moves by saltation which is the snow and ice crystals bouncing along the surface until they leap off cliffs becoming an aerosol snow dust in the atmosphere which is sublimated into thin air. This same process is also why all the rock hard ice disappears from the road surface in the wind areas.

Excellent Observations <here> thanks to Scott, G-ram, Jay, Gareth, Trevor, and Alex (more than one Alex?).

Recent Avalanche Activity

March 21: Windslabs to size D2 continue to release, including onto the highway at Milepost 23.
March 19-20: Numerous windslab releases to size D2 observed between Mileposts 22 and 29 across Thompson Pass with the initial onset of the present extreme northerly wind event, transporting available soft snow.
March 17: D2 Wind slab, upper elevation, north aspect inter-mountain snow climate zone, accidental human triggered one foot deep, 30 feet wide, ran 450 feet.
March 16: D1 Storm slab, intentional human triggered.
March 14: D2 Storm slab, intentional human triggered.

 

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 12 / 18
Ridgetop Wind Forecast (direction/mph): NE / 55-105
Snowfall (in):  0″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  22 / NE   75 / NE
Max Wind Gust (mph) / Direction  39 / NE  100 / NE
Temperature Min / Max (*F)  31 / 40  10 / 22

Weather Forecast:    Beautiful clear skies until Saturday with strong to extreme (>40 mph) northerly outflow winds forecast to well exceed hurricane force (73 mph) into Thursday. Temperatures dropping to single digits overnight and raising into the twenties during the day. Stunningly beautiful vistas. Winds abating Friday. Clouds Saturday. Computer models suggest snow next week but would you bet on it?

Additional Info & Media

SNOW HISTORY: Valdez 3/18 AM Thompson Pass 3/20 AM
24 Hour Snow / Water Equiv. 0”/ 0.03″ 2″ / 0.3″
Storm Snow /Water Equiv. (3/9-14) 19” / 0.41″ 40″ / 1.5″
Current Snow Depth 33″ 84″
March Snow / Water Equiv. 20″ / 2.56″ 49″ / 3.6″
Total Winter Snowfall / Water Equiv. 132.54″ / 26.93” 372″ / 36.6″
Snowload in Valdez 55 lbs/sq. ft.

 

SNOW DEPTH & WATER SURVEY (3/4/2018) Depth Snow Water Equivalent
Milepost 2.5 Valdez  32.2″  9″
Milepost 18 42″ 11″
Milepost 29 Worthington Flats 62.4″ 21.2″
Milepost 37 Tsaina River bridge 58.4″ 14.2″
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