Saturday-Tuesday 1/14-1/17

Issued: Sat, Jan 14, 2017 at 8AM

Expires: Tue, Jan 17, 2017

HEAVY PRECIPITATION CONTINUES TO RAPIDLY INCREASE THE AVALANCHE HAZARD TODAY WITH ANOTHER 15 INCHES OF SNOW TO ARRIVE BY LATE AFTERNOON.

Travel in familiar and conservative terrain as poor visibility and increasing avalanche hazard is not a great combination.

Utilize safe travel habits, limiting exposure and traveling one at a time while in and below avalanche terrain.

As new snow buries the old, remember the slick and weak surface conditions that you have come across in the last week and expect poor bonding until proven otherwise.

Above 2,500ft High

1,800 to 2,500ft Considerable

Below 1,800ft Considerable

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

SATURDAY SUNDAY MONDAY & TUESDAY

DANGER SCALE

STORM SNOW:
Elevation: 
All
Aspect: 
All: strong NE winds were channeling through the pass until the SE took over last night.
Terrain: 
Most suspect are slopes greater than 35*, with either firm or weak old snow surfaces, that are unsupported with many trigger points scattered in the start zone.
Sensitivity: 
Touchy
Distribution:
 Widespread
Likelihood (Human Triggered): 
Possible
Size: 
Small – Large
Danger Trend: 
Increasing 
Forecaster Confidence: 
Good

PERSISTENT SLAB:
Elevation: 
Mostly above 2500′
Aspect: 
All
Terrain: 
Steep rocky slopes where facets exist under old and between windslab, especially interior of Thompson Pass
Sensitivity: 
Stubborn
Distribution: 
Specific
Likelihood (Human Triggered): 
Possible
Size: 
Small – Large
Danger Trend: 
Increasing with extra snow load
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: With 1.5 ft here, and another 15 inches to come today, keep tabs on how well the snow is bonding to old, firm surfaces that are primed for acting as a bed surface.  On Friday, the new snow was failing within the new, low density snow that barely wanted to form a slab. On the colder, north side of the pass (where it was still 0*F), there was a lower density, new snow layer deeper, just above the old surface. This weakness supported more of a soft slab failure in steep, unsupported areas. Luckily, the initial snow seems to be sticking to old surfaces along the highway corridor. Is this also true at the higher elevations? How are the strong and variable gap winds at passes and ridge-tops moving and compacting all this new snow?

To complicate things, certain areas likely have developed weak crystals such as near surface facets and surface hoar in wind protected areas. Consider how these weak and problematic snow forms will ease the release of new snow load building on top of them.

Our last storm ended New Year’s Eve. Until Jan 12th, it has been clear, mostly cold, and windy. The extreme outflow wind event that started late Jan 5th had gusts to 104 mph on Thompson Pass and 98mph in Valdez creating a haze of airborne snow filled the skies as the soft snow sublimated into the atmosphere. Unfortunately, the snow was dramatically thinned and peeled back to rocks and early season snow once again. Alders that were once laying down are popping back.

This thinning of our snowpack combined with cold temperatures didn’t do much for strengthening the snow structure. Weaknesses still persist near the ground and mid-pack in many areas. This significant precipitation event will hopefully crush and flush out many areas harboring weak snow grains. Plan for the possibility of moving storm snow to easily stress and step down into these deeper, weak snow layers….resulting in much larger than predicted avalanches with large, hard slab blocks in the debris.

coastal-zone-iconMaritime (Coastal):
This zone, consistently warmer than inland, has a relatively stronger, more predictable snow structure. If you can navigate your way through the lower elevation alder, soft snow can be found in wind protected alcoves.

intermountain-zone-iconInter-mountain (Transitional):
A large variance in depth and structure defines this zone’s snowpack structure. Weak, early season facets at the ground and between layers of windslab remain a concern, especially on steep, shallow and unsupported slopes. Many of the storms this season have not pushed interior very far, so inland of passes, the snow is generally thinner and more questionable. It has been colder on the interior side as well, preserving persistent weak layers. In the upper Tsaina Valley and north of Mile Post 36 along the highway corridor, the snow is reacting very similar to the continental region: weak, shallow structure that fails easily when loaded.

interior-zone-iconContinental (Interior):
More interior beyond Mile Post 46 and out past Billy Mitchell, the snowpack is thin and incredibly weak: mostly facets. Recent avalanches have stepped down to ground. This structure will not change until a significant storm rolls inland.

Find more photos and observations at the bottom of the page. Sharing your observations helps others make informed decisions.

Recent Avalanche Activity

coastal-zone-iconMaritime (Coastal):

  • Visibility has limited new observations.

intermountain-zone-iconInter-Mountain (Transitional):  The January 6 extreme wind event triggered numerous avalanches inland of Thompson Pass many releasing to ground, again reminding us of the dangers of the buried weakness of sugar snow (facets) at the ground) now covered with 2-3 feet thick hard windslab.

interior-zone-iconContinental (Interior):

  • Visibility has limited new observations.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  13/28
Ridgetop Wind Forecast (mph/direction): 15-35/SE
Snowfall (in):  12-15″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  7?/NE  22/Var
Max Wind Gust (mph) / Direction  16?/NE  38/SE
Temperature Min / Max (*F)  24/31  2/29

Weather Forecast: About 16 inches has accumulated in town and on the pass in the last 24 hours and that looks like it could double by this afternoon. Late last night, the warm front and onshore SE winds finally overpowered the interior NE outflows forcefully pushing over Thompson Pass. Temperatures have risen significantly on both sides of the pass. Precipitation will let up this afternoon (maybe see some flakes here and there) until another low pushes right past us, bringing more snow from mid-Sunday until early Tuesday…..Round 2!

 Screenshot (48)_snipScreenshot (46)_snip

Additional Info & Media

SNOW HISTORY: Valdez 1/14 AM Thompson Pass 1/14 AM
24 Hour Snow / Water Equiv. 16.5” /1.22” 17?″ /1.4?″
Storm Snow /Water Equiv. (1/12-1/?) 18.5” /1.22″ 3″ /0.2″
Current Snow Depth 39″ 17″
January Snow / Water Equiv. 22.6″ /1.6″ 2″ / 0.1″
Total Winter Snowfall / Water Equiv. 97.9″ / 11.2” 145″ / 14.5″
Snowload in Valdez 23 lbs/sq. ft.

img_20161228_130954img_20161228_130730

Photos of our new Nicks Valley Weather Station Python to the east, Berlin Wall to the west.

SNOWFALL for LAST 24 HRS at OTHER STATIONS:
Nicks Valley at 4200 ft (in): 10″
Upper Tsaina at 1750 ft (in): 10″
Sugarloaf at 550 ft (in): 13″
SNOW DEPTH & WATER SURVEY (1/3/2017) Depth Snow Water Equivalent
Milepost 2.5 Valdez  22.7″  4.7″
Milepost 18 27.9″ 5.9″
Milepost 29 Worthington Flats 44″ 9.9″
Milepost 37 Tsaina River bridge 33.8″ 5.6″
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 VAC Forecasts.

Forecaster: Kevin Salys