The 12/5-12/6 storm that deposited 2 feet of snow in Valdez and 12-16″ on Thompson Pass has increased the depth of the slab that is sitting on the November facets. Northeast winds have kicked up the morning of 12/8 which will add more stress and increase the likelihood of human triggered avalanches in wind channeled terrain.
There are many things that are unclear about our snowpack at the current moment. What is clear is that we have a persistent slab avalanche problem. What is unclear is how sensitive this layer is to human triggers at the present moment. With red flags present as recently as 12/7, like large collapses and shooting cracks it is safe to assume that slopes steeper than 32° are reactive to human triggers. Stability tests have also showed propagation 2 feet deep in the pack. Currently it would be wise to maintain a caution approach and avoid terrain with consequences.
The 24 hour rule will not apply for our current setup. The only successful mitigation practices for a persistent slab avalanche problem are patience, and a conservative approach in choosing terrain. Good protocols are very important as well during this type of avalanche problem ie: only exposing one person at a time to an avalanche prone slope, good communication and having an escape route should a slope fail.
Some important things to remember about a persistent weak layer problem is that tracks are not a sign of stability. A slope can fail after many tracks have been laid down. Also it will be possible to trigger avalanches remotely meaning a slope that is above you or adjacent to your position.
Photo of 1cm+ chained facet found buried 40 cms (16″) on Catchers Mitt 3500′ SE aspect.
Northeast winds have kicked up to gusts in the high 30’s at Thompson Pass. Expect to find fresh wind slabs up to 2 feet in depth in wind channeled terrain that will be reactive to human triggers. Wind slab avalanches will have the potential to step down into deeper faceted layers in our snowpack (see problem 1) and produce larger avalanches. Avoid recently wind loaded slopes in terrain steeper than 32°.
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 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 WEDNESDAY 12/08 THURSDAY 12/09
TIME (LT) 06 12 18 00 06 12 18 00 06
CLOUD COVER BK FW SC SC SC OV OV OV OV
CLOUD COVER (%) 65 10 35 35 40 95 100 95 90
TEMPERATURE 19 14 5 1 3 16 16 15 18
MAX/MIN TEMP 19 -1 18 14
WIND DIR NE NE NE NE E E E SE E
WIND (MPH) 16 8 6 8 8 17 28 13 11
WIND GUST (MPH) 40 26 26 26 26 36 47
PRECIP PROB (%) 5 0 5 10 20 80 100 100 70
PRECIP TYPE S S S S S
12 HOUR QPF 0.00 0.00 0.10 0.38
12 HOUR SNOW 0.0 0.0 1.5 6.6
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 as of 11/29
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. This indicates we have moved into persistent slab avalanche territory.
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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