Today is another day where human triggered avalanches are likely and natural avalanches are possible.
Another round of snowfall is impacting our area over the next 24-36 hours. This storm is coming in colder than the last set with snow currently falling to sea level. This may change today with snow line forecasted to rise to 1000 feet by this evening. Our area has received 4-10 inches so far depending on proximity to the coast (Coastal locations recieving more snow). 6-12 additional inches of snowfall is expected before the current storm departs.
Storm slabs are forming on a variety of surfaces ranging from a little bit of snow on stout rain crusts at low elevations to older storm/wind slabs from last weekend at upper elevations. New snow may become upside down at low elevations if the forecast proves true and snow levels rise to 1000 feet. Above the freezing line new snow will be added stress to wind slabs that were previously sensitive. We may also receive enough new snow that new storm slabs form widespread instability on slopes steeper than 30°.
Added to that winds are forecasted to be moderate to strong today and have switched directions from SE to NE at the surface. At upper elevation winds are expected to remain SE. This may sound confusing, but the takeaway should be that you should expect to find fresh wind slabs on a variety of aspects. New snow avalanches may be able to step down to deeper layers in the snowpack and create very large destructive avalanches (see problem 3).
There is a lot of uncertainty out there at the moment as to the variable depths of storm slabs from the last week and how well they are bonding. What we are certain of is that precipitation has been occurring over the past 9 days atop a snowpack with poor structure on Thompson Pass and areas north. If you choose to recreate in avalanche terrain today it will be important to pay attention to red flags that the snow gives us. These include: Shooting cracks, collapsing, active wind loading, and natural avalanche activity.
The forecast currently indicates for the snow line to rise to 1000 feet as the day goes on. This would create the possibility to trigger wet loose avalanches in steep terrain at low elevations. Be aware that wet loose slides often have more force than expected and can be hazardous if they are able to carry you into dangerous terrain, ex: cliffs or terrain traps. Pay attention to the density of the snow surface and use caution in steep terrain if rain begins to fall on dry snow.
This avalanche problem will not exist today if the forecast does not prove true and snowfall continues down to sea level.
In many locations developed facets exist in our mid to lower snowpack. These facets have been stressed by warm temperatures and heavy precipitation. These weak layers will need time to adjust to the added weight that the recent storms have delivered. 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.
Storm 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.
1/22-1/24- 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
...WINTER WEATHER ADVISORY REMAINS IN EFFECT FROM 6 AM THIS
MORNING TO 9 AM AKST FRIDAY THROUGH THOMPSON PASS...
* WHAT...Blowing snow expected. Total snow accumulations of 6 to
12 inches. Winds gusting as high as 35 mph.
* WHERE...Thompson Pass.
* WHEN...From 6 AM Thursday to 9 AM AKST Friday.
* IMPACTS...Plan on slippery road conditions. Areas of blowing
snow could significantly reduce visibility to one half mile or
less at times.
* ADDITIONAL DETAILS...Gusty winds and snowfall will continue
through Friday morning. Snow becomes light and begins tapering
off by Friday afternoon. Winds will continue to be gusty beyond
Friday and any transportable snow on the ground may result in
periods of reduced visibilities.
Point forecast for Thompson Pass
Detailed forecast for Thompson Pass (mid elevation 2000-4000′)
DATE THURSDAY 01/27 FRIDAY 01/28
TIME (LT) 06 12 18 00 06 12 18 00 06
CLOUD COVER OV OV OV OV OV OV OV OV OV
CLOUD COVER (%) 100 100 100 100 95 95 95 85 90
TEMPERATURE 21 23 23 22 21 21 19 16 14
MAX/MIN TEMP 23 21 22 12
WIND DIR NE NE NE NE NE NE NE NE NE
WIND (MPH) 13 16 14 14 16 16 8 9 11
WIND GUST (MPH) 34 34 34 34 35 35 34 34 34
PRECIP PROB (%) 100 100 90 90 70 70 70 40 40
PRECIP TYPE S S S S S S S S S
12 HOUR QPF 0.45 0.23 0.19 0.07
12 HOUR SNOW 6.8 3.3 2.7 0.5
SNOW LEVEL (KFT)0.5 0.8 1.0 0.9 0.7 0.1 0.1 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. Our area has received measurable precipitation the last 9 days, with another strong pulse expected today. Multiple avalanche problems exist. Human triggered avalanches are likely 1-3+ feet deep and natural avalanches are possible.
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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