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.
Strong north winds have returned to our area and will be redistributing the new snow that fell on Monday and Tuesday into fresh wind slabs. Expect for wind slabs to be initially reactive to human triggers in specific locations. Wind slab depths in the Maritime climate zone will be in the 1-3 foot range were 10″ of storm snow fell at sea level 12/5-6. In the Intermountain and Continental zones expect to find new wind slabs to be about half that depth. Places to watch out for will be the lee side of high elevation ridge lines (SE-NW),cross loaded gullies and the lee side of terrain features. Pillowed snow surfaces, freshly formed cornices and shooting cracks are all indicators of a freshly loaded slope.
Low friction (slick) bed surfaces are in place under new slabs that will allow for avalanches to run fast on large slopes. Keep in mind that wind slabs are the most reactive during or directly after formation. Pay attention to wind distribution patterns and plan your route accordingly.
Thin (weak) snowpacks can not handle the sudden changes that a strong (thick) midwinter snowpack can. As snow and weather conditions change expect to encounter areas of unstable snow.
There are multiple rain crusts from October that are faceting in the mid and lower snowpack. Late November winds created very strong snow above these layers making it difficult for a person or machine to affect. Newly formed wind slabs are adding stress to these layers. At this point, it is unlikely that we have received enough new snow/load to overcome the strong bridging affect of the wind damaged snow from late November that is near the surface. We can not rule out that smaller storm snow or wind slab avalanches could have enough force to step down to these deeper layers.
Affecting this avalanche problem is currently unlikely, but will likely become a problem later in the season once we begin to receive some significant snow.
There is a higher possibility of affecting these layers in the continental zone where a more faceted snowpack exists.
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
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 Wednesday 12/07/22 Thursday 12/08/22
Time (LT) 06 12 18 00 06 12 18 00 06
Cloud Cover OV OV OV OV OV OV BK BK BK
Cloud Cover (%) 100 95 95 90 75 75 60 65 65
Temperature 26 25 23 19 14 13 12 10 10
Max/Min Temp 26 14 15 7
Wind Dir E NE N N N N N NE N
Wind (mph) 8 12 29 33 31 32 28 26 16
Wind Gust (mph) 27 36 48 49 52 57 51 46 36
Precip Prob (%) 90 20 10 10 10 10 10 10 10
Precip Type S S
12 Hour QPF 0.06 0.00 0.00 0.00
12 Hour Snow 0.6 0.0 0.0 0.0
Snow Level (kft) 0.3 0.1 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.
The avalanche hazard is Considerable above 1500′ in the Continental zone. Strong north winds are currently moving the new snow from Monday and Tuesday into fresh windslabs. Human triggered avalanches will be likely in specific locations up to 1 foot in depth. Watch for signs of instability such as shooting cracks, collapsing and recent natural avalanche activity.
Posted by Gareth Brown 12/8 7:00am.
For a description of avalanche problems, weather information, season history and more click the (+ full forecast) button. Avalanche forecasts will be issued Wednesday-Sunday.
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