Sunday-Wednesday 3/4-3/7

Issued: Sun, Mar 04, 2018 at 8AM

Expires: Wed, Mar 07, 2018

Choose routes that avoid windslab on steep slopes – if it sounds hollow, shoots crack, or collapses underfoot, you are on windslab. Talk about the consequences of the slope your group is committing to; is there a better option?

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
2-moderate 2-moderate

DANGER SCALE

 

WIND SLAB:
Elevation:   Above 2000′
Aspect:   Lee of ridges, gullies, ridgetops
Terrain:   Upper elevation terrain exposed to wind
Sensitivity:   Touchy-Responsive
Distribution:   Specific
Likelihood (Human Triggered):   Possible
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): 
 Unlikely
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:  A skiff of snow fell Saturday evening. Sunday, north outflow wind is picking back up, so expect redistribution of loose snow, building fresh windslab near ridgetops and channeled areas. High to extreme winds  Feb. 27 – Mar. 1 scoured exposed terrain and eroded into older snow layers.  The snowpack depth varies widely due to these wind events scourly down to rock and heather, while just lee of ridges there are pockets of windslab meters deep.

The Feb. 26 and Feb. 27 storms totaled 12″ (30cm) on the pass.  The Feb. 22 storm brought 4″ to Valdez and 6″ to the Pass and interior.  North wind transported that new snow, and built  windslab lee of ridges and gullies.

The combined effect of steady winds and sparse snow events has produced notable density and depth differences in the upper snowpack.  The cold, clear weather between the 1/15 and 2/13 storms grew a weak layer that the next storm snow did not adhere to very well.

Due to that layer of facets (sugar snow), 2-6′ (60-180cm) beneath the surface, a persistent slab concern still exists. We’re still tracking the distribution above 2500′ and our recent snowpit tests are indicating this layer may no longer be widespread.  The bottom line is that these persistent weak layers are stubborn to trigger, but due to depth, will have higher consequences if a rider, or riders, find the trigger point; be cautious near thinner areas near rocks and the edges of slabs.

 

Recent Avalanche Activity

There was a possible human triggered windslab avalanche Saturday in the Wortman’s area. No further details known at this time.

Feb.28 the rock bluffs near the Richardson Hwy hairpin at mile 23 popped off windslabs that covered the road.

Feb. 28 – Mar.1 Many naturally triggered windslab avalanches to size 2 released from ridgetops and crossloaded gullies in the mid and upper elevations.  See observations page for details.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 12 / 20
Ridgetop Wind Forecast (direction/mph): NE/9-33
Snowfall (in):  0″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  14 / ENE   15 / NE
Max Wind Gust (mph) / Direction  32 / ENE  39 / ENE
Temperature Min / Max (*F)  23 / 37  6 / 25

Weather Forecast:

Clear with north outflow wind picking up again Sunday. No precip on the horizon.

Additional Info & Media

SNOW HISTORY: Valdez 3/4 AM Thompson Pass 3/4 AM
24 Hour Snow / Water Equiv. 0.01”/ 0.01″ 0.01″ / 0.01″
Storm Snow /Water Equiv. (2/27) 6” / 0.25″ 4″ / 0.2″
Current Snow Depth 30″ 84″
February Snow / Water Equiv. 24.9″ / 2.25″ 31″ / 2.7″
Total Winter Snowfall / Water Equiv. 112.95″ / 24.38” 317″ / 33″
Snowload in Valdez 49 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS / STORM TOTAL (Feb. 27) / 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.
Sarah Carter

Forecaster: Sarah Carter