Northeast winds have been forming windslabs up to 3 feet deep in wind channeled terrain. These have been sensitive to human triggers as recently as 1/28. As our current storm exits and skies begin to clear northeast wind may become more widespread, and begin to form fresh windslabs in more places. Current forecast are indicating wind speeds of 30 mph increasing to 40 on Thursday. This will be enough to redistribute new snow into slabs that will be initially reactive to human triggers in specific places. The most likely places to encounter instabilities will be on the lee side of ridge lines and cross loaded gullies. Lucky for us, wind slabs are fairly easy to recognize. They often have a pillowed or smoothed over look and will be stiffer than the snow that is below. Snow texture can be a good indicator as to wind direction and where slabs will exist, fresh wind lips will point towards wind slabs. Red flags such as shooting cracks will often exist where sensitive wind slabs are present. The hazard will be lower in areas unaffected by wind.
Wind slabs may be able to step down to deeper layers in the snowpack creating very large avalanches (see problem 2).
We are on the tail end of a prolonged period of storms with clearing possible today for the first time since 1/20. Use caution today if you decide to travel in avalanche terrain. There are many tools that you can utilize to asses stability before exposing yourself and your group to avalanche terrain with consequences. Hand shear tests and the use of test slopes are an easy way to gain more information as to how well the surface snow has bonded. Pole probing is a quick way to identify weak layers (strong over weak). Pay attention to wind direction and the amount of snow transport that is happening. What slopes are being loaded in the area where you are traveling? Lastly, terrain progression is one of our most important tools. This means that we begin on smaller slopes with little to no consequences to asses snowpack stability and slowly work up towards bigger terrain as we have a clearer picture of stability conditions. When we see signs of stability we may take a step forward, when red flags are present we take a step back. This process can take multiple days.
In many locations developed facets exist in our mid to lower snowpack. These facets have been stressed by continued heavy precipitation and wind forming deep slabs. These weak layers will need time to adjust to the added weight that the recent storms have delivered.
It is very difficult to predict how much of a load these facets can handle before failing. In the short term it would be wise to assume that very large persistent slab avalanches remain a possibility while the snowpack is being actively loaded by wind. In many areas above 3000′ these facets have been capped by knife hard wind slabs making them more difficult to affect. Pole probing often along your route is a good way you can determine what’s overlying faceted snow in our lower snowpack.
Wind slabs may be able to step down to these weak layers creating very large destructive avalanches. The most likely place to encounter this avalanche problem is in the Continental zone in thin rocky areas where weak faceted layers are more easily affected.
(2mm grid) Photo of chained facets found in the low elevation area of Girls Mountain 1/13. In many areas these facets are capped by knife hard wind slabs making them difficult to affect and detect.
1/28- During brief break in the clouds, observed a Natural D3 avalanche on Catchers Mitt. It is likely this slide failed on a persistent weak layer, as the crown was deep ~4-5 feet and ran a considerable distance.
1/22-1/24- A D3 natural avalanche was observed on 1/22 in snow slide gulch that ran to just below the summer trail.
On 1/26 2-D3 naturals were seen on the east face of Mt Tiekel (beyond forecast zone) that ran half way through their aprons. These likely occured between the 1/22-1/24 time period.
Clouds prevented observation of where these slides originated
1/22- Clouds made observing avalanche activity difficult, although numerous large wet loose slides were observed on south aspects of Town Mountain in the Port of Valdez.
1/13- Multiple large natural avalanches were noted following the snowfall on 1/13. Most were near high elevation ridge lines, although mid elevation storm slabs were noted on north aspect of Catchers Mitt and south aspect of Mile high. Other avalanche not shown in photos include Goodwills north aspect and Oddeyssey north aspect.
1/1-1/4- The new years day wind event created an avalanche cycle that was difficult to document due to crowns being rapidly reloaded by 80 mph winds. Below are photos of a couple very large slides that were still visible in the Hippie ridge area. Naturals were also noted on Three Pigs, 40.5 Mile, Crudbusters, Python Buttress.
12/29- Multiple natural wet loose D1-D2’s were observed in the Port of Valdez with no step downs noted.
12/23- Berlin Wall north face ~5000′ HS-N-R3-D2-O. It is possible this occurred on 12/21, although it was not observed until 12/24.
12/21- Numerous natural avalanches observed all along the north side of Thompson Pass, as a result of strong NE wind event along with a couple inches of new snow and rising temperatures. Observed naturals on all aspects except windward slopes with crowns originating from 1000 feet to 5500 feet in elevation. Most of these were hard slab avalanches. Crown depths were difficult to discern due to reloading, although some crowns looked to be up to 2 meters in depth.
12/19- D 2.5 natural avalanches were observed on the north facing buttress west of Gully 1 and Schoolbus.
12/14- Several natural avalanches were observed although poor visibility prevented a full view of the action. The most notable natural was observed in Nicks Happy Valley on a NW aspect ~4000′. Crown depth was not visible. Debris ran down the valley and piled up at the typical snowmachine pickup.
12/8- Large remote trigger/ sympathetic avalanche event occurred 12/8 with avalanches extending from Gully 1 to Nicks. Avalanches were soft slabs that ranged in size from D1-D3. Over 10 separate avalanches were counted with crown depths averaging 2-3′. One avalanche had a crown length of half a mile while another was triggered over a mile away from the point of collapse. See observation section for full report and more photos.
12/7- Only a few natural avalanches were noted during the last storm. It is likely there were more during the storm, but crowns may have been filled in by subsequent wind and snow.
D2’s on Town mountain was observed ~3000′
A couple of D2’s were noted in N. Oddessey gully and Big Oddessey.
D2 on 40.5 mile peak ~5500′.
12/2-12/3- Several natural D2 avalanches were noted on south aspects of Three pigs, Hippie Ridge and Averys. These windslab avalanches originated between 4000-5500 feet elevation.
NWS Watches and Warnings
Point forecast for Thompson Pass
Detailed forecast for Thompson Pass (mid elevation 2000-4000′)
DATE SATURDAY 01/29 SUNDAY 01/30
TIME (LT) 06 12 18 00 06 12 18 00 06
CLOUD COVER OV OV OV BK FW FW FW FW CL
CLOUD COVER (%) 85 80 80 55 25 10 10 5 0
TEMPERATURE 14 16 15 11 8 10 5 1 0
MAX/MIN TEMP 17 7 12 -2
WIND DIR NE NE NE NE NE NE N NE N
WIND (MPH) 23 18 13 17 20 23 20 17 12
WIND GUST (MPH) 32 40 40 40 36 34
PRECIP PROB (%) 50 50 50 20 5 0 0 0 0
PRECIP TYPE S S S S
12 HOUR QPF 0.07 0.05 0.00 0.00
12 HOUR SNOW 0.0 0.0 0.0 0.0
SNOW LEVEL (KFT)0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Snow and Temperature Measurements
All snowfall measurements are expressed in inches and temperature in Fahrenheit. 24 hour sample period is from 6am-6am.
* 24 hour snow water equivalent/ SWE.
** Season total snowfall measurements for 46 mile began December 1st.
Season history graphs for Thompson Pass
Click on links below to see a clear and expanded view of above Season history graphs
TP WX Nov 21
TP wx Dec 21
TP wx as of 1/6
Winter weather began early this season, with valley locations receiving their first snowfall on the last day of Summer (September 21st). Following this storm, above average temperatures and wet weather occurred from late September through early November. During this time period Thompson Pass received 96 inches of snowfall by November 7th and Valdez recorded 7.73″ of rain.
After the 7th of November our region experienced a sharp weather pattern change. Temperatures dropped below seasonal norms and snowfall became infrequent. Between the time frame of November 7th- November 28th Thompson Pass only reported 19″ of snow with 1.1″ of Snow water equivalent (SWE). Temperatures remained below 0° F for most of the period. This cold/dry weather caused significant faceting of the snowpack, with poor structure the result.
Moderate snowfall returned to our area the last day of November and deposited 6-12 inches of new snow. The amount varied depending upon the locations’ proximity to the coast. As the storm exited on the 2nd of December it was quickly replaced by moderate to strong northeast winds.
On 12/5-12/6 Valdez received 2 feet of new snow with Thompson Pass reporting 16″. Blaring red flags like collapsing, shooting cracks and propagation in stability tests were immediately present. On 12/8 a significant remote/ sympathetic avalanche event occurred from Gully 1 through Nick’s Happy Valley.
Strong outflow winds began on 12/11 with periods of light snowfall. This has caused slab thicknesses to become variable in areas exposed to NE winds.
A fair amount of natural avalanche activity occurred during the 12/11 wind event mostly on southerly aspects. The week following this wind event fairly benign weather occurred which allowed the snowpack to adjust and for stability to improve although snowpack structure has remained poor.
On 12/21 our area received a couple inches of snow along with temperatures rising and strong outflow winds. This combination of weather kicked off a fairly significant natural avalanche cycle. Many of the slabs appeared to be deeper wind slabs that were created from the 12/11 wind event. These failed on faceted snow created in November. The event is yet another indicator of our poor snowpack structure and its inability to receive any major change in weather without the avalanche hazard rising in conjunction.
On 12/26-28 warm air moved in at elevation and caused light rain to fall up to ~4000′. A very thin rain crust was formed in many locations that was unable to support a persons weight.
A prolonged period of strong north winds began on new years day with wind speeds reaching 80 mph. As winds tapered to 30-40 mph on the 5th temperatures plummeted with lows exceeding -30 F in the Tsaina valley.
Snowfall returned to our area on 1/13 with a foot of snow reported on Thompson Pass. An additional ~6 inches of snow were received on 1/15 with settled storm totals of 2.5 feet above 5000′.
Moderate outflow winds kicked up on 1/16, but were short-lived and not wide spread. This was followed by two days of calm and mild weather.
On 1/21 a big pattern change occurred with several large Pacific storms delivering rain up to 3000′ and heavy snowfall above.
The avalanche hazard is Considerable at all elevations. Human triggered avalanches are likely and natural avalanches are possible 1-3 feet deep. The most likely place to trigger an avalanche will be areas recently loaded by northeast wind. Watch for signs of recent wind loading such as shooting cracks, hard snow over soft and pillowed snow surfaces.
Click the + Full Forecast button below for a list of current avalanche problems, travel advice, weather resources and more.
Help to improve your local avalanche center and contribute an observation to the website. You can also contact me directly at [email protected] (907) 255-7690.
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