The Avy Rose shows the forecasted danger by elevation and aspect.
It adds more detail about where you are likely to find the dangers mentioned in the forecast. The inner circle shows upper elevations (mountain top), the second circle is middle elevations, and the outer circle represents lower elevations.
Think of the Rose as a birds-eye view of a mountain, looking down from above. The rose allows our forecasters to visually show you which parts of the mountain they are most concerned about.
As the latest storm exited North winds began with moderate to strong gusts occurring overnight in Valdez and at the Nicks Snotel at 4100′. There is a significant amount of new snow available for transport that will allow deep wind slabs to quickly form. Expect for areas that have recently or are actively wind loading to be sensitive to human triggers. Pay attention to what aspect you are traveling on and where the wind is redistributing snow. Signs of instability such as shooting cracks, collapsing and recent avalanche activity all indicate that a slope has the energy required to produce an avalanche. You can manage your risk today by making conservative terrain choices. Our snowpack has just undergone a lot of stress, and strong North winds over the weekend will keep applying stress. Expect for the hazard to remain elevated.
Decreasing temperatures overnight will allow for new snow that has fallen to slowly gain strength. This process takes time and it remains likely to trigger avalanches that involve part, or all of the new snow that has fallen over the last week. Rising temperature occurred near the tail end of this storm which will have created top heavy storm slabs that will likely remain sensitive to human triggers in steep and/or convex terrain. Test slopes and hand pits are good way to see how well new snow is bonding. The bottom line is we have received a significant amount of new snow on a thin snowpack and it will take time for the snowpack to settle and instabilities to go away. In the meantime dangerous avalanche conditions exist.
In addition to new snow being a concern, faceted snow exists at the base of our snowpack. In many areas our snowpack has doubled in a short time period. This has significantly increased the stress on faceted (weak) snow near the base of our snowpack. It is possible that a person could directly affect these layers, or through storm or wind slab avalanches stepping down to these layers. This avalanche problem will be deep enough in some areas that signs of instability may not be present. The most likely area to trigger persistent slab avalanches will be in thin rocky areas where previous facet growth was the most significant. This problem takes longer to heal than a storm slab or wind slab avalanche problem would and carries higher consequences.
11/14- Debris from a D3 natural avalanche at snow slide gulch ended 100 vertical feet above the Lowe river.
Large avalanches (D2-2.5)also occurred in multiple other locations including Berlin Wall, Catchers Mitt, South Three Pigs and Billy Mitchell. The activity extends beyond this list, and mostly occurred during the peak of warming and precipitation on 11/13.
Multiple natural D1-1.5 avalanches were observed on multiple aspects at low elevation. No step downs noted.
12/1- 2 D2.5 natural avalanches were noted on Three Pigs (Beaver slide, Pig Leg). Pig leg ran into the top 1/3 of the fan and Beaver Slide stopped near the end of its track. These both likely occurred during the outflow wind event 11/26-11/29.
D2 natural wind slab was observed on 40.5 mile peak on a west aspect ~3000′. Crown depth range estimated 1-2 feet and 200′ long
12/9- Several D2 natural wind slab avalanches were observed on S-W aspects at mid elevation in the intermountain region. Crowns appeared to be 1-3 feet deep. Catchers Mitt and Gully 1 were among the spots affected.
12/12- Observation of natural activity was prevented by clouds and continuing snowfall on Thompson Pass and Valdez.
12/15- DOT avalanche control work produced several D2-2.5 avalanches from upper elevations of Hogsback. Stepdowns were noted with on slide suspected of failing at the ground. Cloud cover prevented clear observation of avalanche activity.
Check out our updated weather tab! A collection of local weather stations are available for viewing with graphs and tabular data included.
NWS Watches and warnings
NWS Point forecast for Thompson Pass
Date Friday 12/16/22 Saturday 12/17/22
Time (LT) 06 12 18 00 06 12 18 00 06
Cloud Cover CL CL CL CL CL FW FW SC FW
Cloud Cover (%) 0 0 0 0 5 10 20 35 20
Temperature 10 10 7 3 1 0 -3 -7 -7
Max/Min Temp 12 -3 2 -10
Wind Dir NE NE NE NE NE NE NE NE N
Wind (mph) 27 24 25 23 23 24 18 10 20
Wind Gust (mph) 43 37 39 36 37 37 31 51
Precip Prob (%) 0 0 0 0 0 0 0 0 0
12 Hour QPF 0.00 0.00 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
Click on link below for Thompson Pass weather history graph:
*HN24W- 24 hour Snow water equivalent in inches
*SWE– Snow water equivalent
**46 mile seasonal snowfall total begins December 1st.
Our snow season began with above average precipitation and temperatures. Beginning in September, snow lines generally hung around 4500′ until 10/12. At that point our area received the first snow down to sea level with 12-16 inches on the north side of Thompson Pass.
On 10/15 wet conditions continued with the freezing line rising to 5000′ or higher. As skies finally cleared on 10/22 we were left with a thin rain saturated snowpack capped by a stout rain crust up to 4500′. Above 4500′ much deeper snowpacks existed due to significant early season snowfall at upper elevations.
Dry and cold conditions along with moderate outflow winds finished out the month of October.
On 11/1 precipitation returned with 18 inches of snow and ~1″ of SWE on Thompson Pass. This new snow was initially reactive with several natural D2 avalanches reported on Thompson Pass. These slides were running on a firm bed surface consisting of old rain crusts and old wind slabs from October.
On 11/4 a strong north wind event kicked up with 65 mph+ winds on Thompson Pass. Our snowpack received significant damage as already thin snow below 4500′ was stripped down to old wind slabs, rain crusts and the ground.
Precipitation returned on 11/8 and became heavy on 11/11. Storm totals of around 50 inches were recorded at Thompson Pass DOT between 11/8-11/13. Snow lines rose to ~3000′ near the tail end of the storm with heavy rain occurring in low lying areas.
Skies cleared on 11/14 through 11/18 with a strong temperature inversion setting up. Valley temperatures north of Thompson Pass fell to 0° F with above freezing temperatures existing above 4000 feet. Valdez temps remained mild. This weather allowed for widespread surface hoar up to 1 cm to develop in low lying areas.
Precipitation returned on 11/19, with incremental snowfall on Thompson Pass and areas north. The Valdez area received rain during this period. 12 inches have been recorded at TP DOT between 11/9-11/23.
11/26-11/29- Strong outflow (N) wind event. Many areas below 3000′ were stripped to the 11/13 rain crust, destroying the 11/19 BSH layer. Widespread very hard snow surfaces were the result.
Precipitation returned to our area on 12/5, with higher accumulation amounts near the coast. As storms cleared out on 12/7, they were directly followed by another round of strong north winds. These winds once again incurred severe damage to our snow stripping surfaces back to the 11/13 rain crust on windward aspects and further building pencil hard slabs on lees.
12/11- Significant snowfall event that dropped 12-24 inches+ in a 12 hour period.
12/12-12/15- Steady snowfall continues with short breaks between pulses. Storm ended the night of 12/15 with 2+ feet accumulating overnight above 2000′. Valley locations received heavy rain.
The avalanche danger is Considerable at all elevations. Human triggered avalanches up to 3 feet deep are likely that will be large enough to injure, bury or kill a person. Cautious route finding and conservative terrain choices are recommended as strong north wind will be redistributing the new snow from the latest storm into windslabs.
Posted by Gareth Brown 12/16 8:00am.
For a description of current avalanche problems, weather information, season history and more click the (+ full forecast) button. Avalanche forecasts will be issued Wednesday-Sunday.
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