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Tue, Dec 10, 2019 at 7:21 AM
Issued by: Chris Bilbrey

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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.
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.
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Summary

The snowpack continues to adjust from the recent load. While this was a significant load, the underlying snowpack appears to have taken it in stride. However, if you travel on slopes steeper than about 35 degrees, you can still trigger an avalanche. Slopes facing northwest to north through east harbor weak snow at the ground below a stiff slab and are the most dangerous. Pre-storm observations highlight surface hoar formation and this weak layer is now buried below the recent storm snow. This problem appears more reactive in the Wolf Creek Pass area but don’t rule out its existence further west in the zone.

Weak snow at the ground has become more difficult to trigger but if you do, avalanches will be large enough to bury you. Look for and avoid thick, wind-drifted pillows directly below ridges and in cross-loaded terrain features and heed the warning signs of cracking and collapsing. Winds shifted to the northwest overnight and this may expand the distribution of drifting above treeline. Avalanches triggered in a heavily wind-drifted area have the best odds of becoming larger and propagating across the entire slope. Safer and very enjoyable riding conditions can be found on lower angled slopes.

 

 

Avalanche Problem

 
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N
S
E
W
NW
NE
SE
SW
Above Treeline
Near Treeline
Below Treeline
Certain
Very Likely
Likely
Possible
Unlikely
Historic
Very Large
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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

 
problem icon
N
S
E
W
NW
NE
SE
SW
Above Treeline
Near Treeline
Below Treeline
Certain
Very Likely
Likely
Possible
Unlikely
Historic
Very Large
Large
Small
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

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

What You Need to Know About These Avalanches


Wet Slab avalanches occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoid avalanche terrain when you see pinwheels, roller balls, loose wet avalanches, or during rain-on-snow events.

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) 10 to 15 25 to 30 10 to 15
Wind Speed (mph) 6 to 16 7 to 17 7 to 17
Wind Direction WSW SW WNW
Sky Cover Partly Cloudy Increasing Partly Cloudy
Snow (in) 0 0 0

Archived Forecasts

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Tue, Dec 10, 2019 at 8:07 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.

 


  • Many slopes that were melted to bare ground less than three weeks ago now have continuous snow cover and a more dynamic snowpack. San Juan Mountains. December 9, 2019. (full)
  • We found good stability on below treeline slopes with varying aspects. Facets at the ground in this snowpit have started to round and this layer is only 7 cm thick. Upper Deer Creek, South San Juan zone. December 9, 2019. (full)
  • 4 to 5 mm depth hoar sitting below a 1 meter thick cohesive slab. Northeast-facing slope at treeline. Upper Deer Creek, South San Juan zone. December 9, 2019. (full)
  • Snowpit on a northwest aspect below treeline. December 9, 2019. (full)

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Avalanche Observations
Report Date # Elevation Aspect Type Trigger SizeR SizeD
View Tue Dec 10 - >TL SE SS N R1 D1
View Mon Dec 9 - >TL N HS N R3 D2.5
View Mon Dec 9 - >TL N SS N R1 D2
View Sun Dec 8 - TL E SS N R1 D2

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Field Reports
Report Date Observer Snowpack Obs Avalanches Media
View Tue Dec 10 Chris Bilbrey No Yes (2) Yes (3)
View Mon Dec 9 Chris Bilbrey No Yes (2) Yes (4)
View Mon Dec 9 Mark Mueller No No No
View Sun Dec 8 Mark Mueller No No No
View Sun Dec 8 Matt Entz No No Yes (4)

See All Field Reports

Weather Observations
Station Date Time Temperature Relative Humidity Wind Speed Wind Direction Max Gust 24 Hr Snow
Wolf Creek Pass Wed Dec 11 2:00 AM 19 45 15 216 19 -
Columbus Basin Wed Dec 11 1:00 AM 20 - - - - -
Cumbres Trestle Wed Dec 11 1:00 AM 12 - 0 272 - -
Lily Pond Wed Dec 11 1:00 AM 22 - - - - -
Spud Mountain Wed Dec 11 1:00 AM 22 - - - - 1.0
Wolf Creek Summit Wed Dec 11 1:00 AM 24 - - - - -

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