Friday-Monday 2/17-20

Issued: Fri, Feb 17, 2017 at 8AM

Expires: Mon, Feb 20, 2017

Even more snow and strong onshore winds out of the SE will form sensitive wind slabs on lee terrain features.

Use small terrain as test pieces and investigate for the existence of persistent weaknesses in more interior, continental snowpack.

Tomorrow, February 18, Kyle Sobek is leading a Backcountry & Avalanche Riding Safety Field Session. 9am-4pm. More details. Learn READY RIDER skills.

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

FRIDAY SATURDAY SUNDAY & MONDAY

DANGER SCALE

 

STORM SNOW:
Elevation: All
Aspect: All
Terrain: All
Sensitivity: Responsive
Distribution: Wide Spread
Likelihood (Human Triggered): Likely
Size: Small – Large
Danger Trend: Steady
Forecaster Confidence: Good

WIND SLAB:
Elevation: Above 2000″
Aspect: Lee to SE wind
Terrain: Near ridges, gullies, rollovers
Sensitivity: Responsive
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Small – Large
Danger Trend: Increasing
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

AVALANCHE PROBLEM TOOLBOX <here>

SNOWPACK DISCUSSION:

Maritime (Coastal) Specific: 

Up to a foot more of snow is getting added to the 3.62+” water equivalent in the last 5 days. The snowpack has absorbed large amounts of moisture and settled extensively. This storm has been a classic crush and flush topped off with a nice cold snow icing to the cake: 7 inches yesterday and more today; old instabilities will not be a concern in this maritime zone after this weather has run it’s stint. As the rain soaked snowpack adjusts and solidifies, evaluate how the new snow is bonding to old, icy surfaces.

In the upper elevations, during windows of visibility, flagging of moving dry snow off the peaks in the port was seen. This points to new wind slab formation in the colder elevations above the rain line….estimated at ~3000′.

Snow has filled in and is sticking to rocks.

Soft slab easily peeling off near surface facets. South facing on DOT ridge.

Find more photos and observations at the bottom of the page. Sharing your observations creates an informed community that everyone benefits from at some point.

Recent Avalanche Activity

Maritime (Coastal) Specific: 

Observed Tuesday February 14:

  • wet avalanches to size 2.5 ran full track to sea level between Mineral Creek and Shoup Bay
  • wet avalanches to size 2 off Benzene Peak near Solomon
  • wet avalanches to size 2 fell off steeps of Keystone Canyon
  • wet avlaanches to size 2 ran into Snowslide Gulch above MP 15-16

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  15 / 24
Ridgetop Wind Forecast (direction/mph):  SE / 10-35
Snowfall (in/water equivalent):  7-12″ / 0.64″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  2 / NE  22 / SE
Max Wind Gust (mph) / Direction  11 / E  36 / ESE
Temperature Min / Max (*F)  28 / 34  18 / 22

Weather Forecast:  Snow started to fall in the middle of the night as the Bristol Bay low pushes inland to the NE. We could see up to 12 more inches of snow by tomorrow as the low breaks down and precipitation dissipates. Strong onshore winds out of the SE are hitting our region and drifting snow to lee aspects. Temperatures should be fairly constant, low 30’s in town and low 20 on Thompson Pass, until skies clear Sunday and things will cool off even further.

Additional Info & Media

SNOW HISTORY: Valdez 2/18 AM Thompson Pass 2/17 AM
24 Hour Snow / Water Equiv. 3.1”/0.2″ 1″ /0.1″
Storm Snow /Water Equiv. (2/12-2/17) 30.35” /3.94″ 29″ /3.8″
Current Snow Depth 57″ 51″
February Snow / Water Equiv. 44.3″ /4.5″ 37″ / 4.5″
Total Winter Snowfall / Water Equiv. 222.2″ /20.4” 276″ / 27.1″
Snowload in Valdez 78 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS (2/17 AM)/STORM TOTAL (2/17)/STORM WATER EQUIV.:
Nicks Valley at 4200 ft (in): 1″ / 1″ / 0.1″
Upper Tsaina at 1750 ft (in): 1?” / 1?” / 0.1″
Sugarloaf at 550 ft (in): 1″/ 1″ / 0.1″
SNOW DEPTH & WATER SURVEY (2/1/2017) Depth Snow Water Equivalent
Milepost 2.5 Valdez  41.5″  9.8″
Milepost 18 43.9″ 9.5″
Milepost 29 Worthington Flats 61.5″ 16″
Milepost 37 Tsaina River bridge 42.1″ 9.3″
This survey is done the first week of each month.

Weather Quicklinks:

  • NWS forecast for Northeast Prince William Sound <here>
  • NOAA NWS spot forecast for Thompson Pass <here>
  • Thompson Pass RWIS weather station <here>
  • MP 30 Nicks (Happy) Valley weather station at 4200 feet <here> (scroll to Nicks Valley)
  • Valdez Glacier UAF weather station at 6600 feet <data here> <map here>
  • Further weather resources <here>

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 Maritime Forecasts.

Forecaster: Kevin Salys