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Tue, Dec 10, 2019 at 6:20 AM
Issued by: Chris Bilbrey

Today

 

Tomorrow

Moderate (2) Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully.   Moderate (2) Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully.
Moderate (2) Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully.   Moderate (2) Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully.
Low (1) Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.   Low (1) Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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Summary

Recent snow and strong winds built fresh slabs on top of a weak snowpack. The most dangerous slopes face north, northeast, and east and harbor a stiff over weak snow combination. In those areas you can trigger avalanches large enough to bury you. Some may break below recent storm snow while others may step down and fail on weak layers near the ground.

Looks for signs of wind drifting such as a hard snow surface or smooth rounded pillows of snow. Use extra care if you are traveling in areas below cornices. Cornices are an indication that the wind has been loading the slopes below them. Avoid travel in and around steep cross-loaded gullies or below ridges. You can find safer riding options on lower-elevation slopes, in protected areas without stiffer wind-drifted slabs, and in terrain less than about 35 degrees without steep slopes overhead.

 

 

Avalanche Problem

 
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Above Treeline
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Avalanche Character Aspect/Elevation Likelihood Size

What You Need to Know About These Avalanches


Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.

Avalanche Problem

 
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N
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NE
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Above Treeline
Near Treeline
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Certain
Very Likely
Likely
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Historic
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Avalanche Character Aspect/Elevation Likelihood Size

What You Need to Know About These Avalanches


Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

Avalanche Problem

 
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N
S
E
W
NW
NE
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SW
Above Treeline
Near Treeline
Below Treeline
Certain
Very Likely
Likely
Possible
Unlikely
Historic
Very Large
Large
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Avalanche Character Aspect/Elevation Likelihood Size

What You Need to Know About These Avalanches


Deep Persistent Slab avalanches are destructive and deadly events that can release months after the weak layer was buried. They are scarce compared to Storm or Wind Slab avalanches. Their cycles include fewer avalanches and occur over a larger region. You can triggered them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Avoid the terrain identified in the forecast and give yourself a wide safety buffer to address the uncertainty.

Weather Forecast for 11,000ft Issued Tue, Dec 10, 2019 at 12:45 PM by Jason Konigsberg Statewide Weather Forecast
  Tuesday Night Wednesday Wednesday Night
Temperature (ºF) 9 to 14 21 to 26 8 to 13
Wind Speed (mph) 18 to 28 21 to 31 17 to 27
Wind Direction WSW WSW W
Sky Cover Partly Cloudy Partly Cloudy Partly Cloudy
Snow (in) 0 0 0

Archived Forecasts

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Tue, Dec 10, 2019 at 8:03 AM
Issued by: Chris Bilbrey Statewide Weather Forecast  

Do you remember where you were on November 19? That date is less than three weeks ago and then, we were talking about thin and discontinuous snow cover and barely enough snow to slide on. Turn the page to December 10 and the mountains look a whole lot different and have a much more dynamic snowpack.

There are two snowpack concerns to look out for. The first lies near the surface and the second is at the bottom. Several observations throughout the San Juan Mountains highlight one if not two surface hoar events that are now buried under a cohesive slab. This persistent weak layer will lay silent below a slab until a rider, machine, or a new load collapse these delicate feathers and the snow above comes crashing down. Observations highlight reactive surface hoar near Wolf Creek Pass and in the Telluride area but digging into the snow is the only way to determine its presence. Northerly, wind-sheltered terrain is where this weak layer stayed preserved.

The larger and more dangerous avalanche issue is the October snow that survived at the bottom of the snowpack. This snow metamorphosized into facets and depth hoar and has been reactive with each loading event. It’s now buried under a three to four-foot-thick slab. The stiffness of the overlying slab makes it more difficult for a rider or machine to impact this weak cohesionless layer and trigger an avalanche. If you do find the not so sweet spot, it may propagate wider across the slope than expected and lead to an avalanche that would be difficult to survive. Most likely trigger locations are near the edge of the slab or near rock outcrops where the snowpack in shallow.

Winds shifted from the southwest to northwest overnight. This may increase the distribution of wind-drifted slabs in the alpine. These should be generally small and easy to avoid. You might encounter new drifts on southeast and south-facing slopes forming above a firm melt-freeze crust. These drifts may not bond well to the old snow surface and could move quickly down slope with ski pressure. 

The bottom line is that our snowpack has some complexity to it. Different weak layers and variable snow depths make for tricky conditions. In the deepest areas the snowpack is showing some signs of promise and strengthening. If it continues to snow, we may eventually have less concerns with basal weak layers. However, it’s still too early to determine and caution is advised. Without a careful snowpack evaluation, paying attention to general snow depth, weak layer type and reactivity, you should consider simply avoiding steep slopes that face a northerly or east aspect.

 


  • Another example of the thin snow coverage in the Sangre de Cristo range. Although thin, I would avoid loaded terrain features like the one on sun/shade line. 12/3/19 (full)
  • Snow coverage south of the defunct Conquistador ski area. 12/3/19 (full)
  • Snowpit below treeline in Sangre de Cristo Mountains. The structure does not look great for the future but at the present time there are only very few places where there is enough snow for avalanches. These are heavily cross-loaded gullies. (full)

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Weather Observations
Station Date Time Temperature Relative Humidity Wind Speed Wind Direction Max Gust 24 Hr Snow
La Veta Pass (160w278) Wed Dec 11 2:40 AM 20 70 - 245 - -
Medano Pass Wed Dec 11 1:00 AM 24 - - - - -
South Colony Wed Dec 11 1:00 AM 25 - 1 237 - 1.0

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