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Tue, Dec 11, 2018 at 7:04 AM
Issued by: Brian Lazar

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

You can trigger an avalanche on wind-loaded slopes today. The most suspect slopes are steeper than 35 degrees and face north and east. These slopes received 1 to 2 feet of wind-drifted snow in the last week. Thick slabs now rest above weak, collapsible and soft snow layers. You can identify the slopes where avalanches are most likely by looking for new cornice growth above terrain features with smooth, pillowed fresh drifts. Avalanches in newly-formed drifts can result in avalanches breaking into deeper weak layers resulting in large and destructive avalanches.

If you are unsure how to evaluate which slopes are wind-loaded, you can always minimize your risk to avalanche by choosing slopes that are less than 35 degrees and avoiding travel under steep slopes. You can find safer travel options on slopes facing west, southwest, and south. These slopes have less wind-loading and also lack widespread weak layers.

 

 

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


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


Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Weather Forecast for 11,000ft Issued Tue, Dec 11, 2018 at 4:08 AM by Brian Lazar Statewide Weather Forecast
  Tuesday Tuesday Night Wednesday
Temperature (ºF) 23 to 28 10 to 15 20 to 25
Wind Speed (mph) 20-30 G50 15 to 25 20-30 G50
Wind Direction W W WSW
Sky Cover Partly Cloudy Mostly Clear Partly Cloudy
Snow (in) 0 0 0

Archived Forecasts

  • Select Forecast: Valid

Tue, Dec 11, 2018 at 7:53 AM
Issued by: Chris Bilbrey Statewide Weather Forecast  

The string of rider-triggered avalanches continues in the North San Juan zone with another one reported Monday on Red Mountain Pass. Avalanches, surface cracking, whumpfing collapses, and propagating stability test all point to unstable snow and should be a solid reminder that you can trigger a large and dangerous avalanche. You could trigger a slide from a distance and they could involve the entire season’s snowpack. 

In the race between the rabbit and the tortoise, you can think of weak faceted snow as the tortoise. Until the snowpack becomes deeper, these buried weak layers will only get worse before getting stronger. Time may be the best option. 

Surface instabilities gain strength more quickly and recent warm temperatures will help the surface snow consolidate. Slopes where thick and firm wind-drifted slabs exist above weak snow are most problematic and where we are seeing the most avalanche activity. These slopes are mostly found near and above treeline.

Steep slopes below treeline continue to be touchy in the North San Juan zone. These slopes are where the greatest uncertainty exists. On many below treeline slopes, the snow surface has transitioned to weak and cohesionless. Other below treeline slopes continue to produce propagating results in stability test indicating that the softer surface slab is still sensitive. Although avalanches in wind-sheltered areas may be smaller, you may want to avoid steep northerly or easterly-facing slopes that end in terrain traps like gullies or large stands of trees.

There is a west-to-east gradient in danger across the Southern Mountains with the bulls-eye of instability in the mountains around Silverton and Telluride. Evaluate snow and terrain carefully and identify wind-loaded terrain features of concern. This will help reduce your risk to avalanches. In the end if stability is the question, terrain is the number one answer.

 

 


  • Mostly wind stripped but also some cross-loaded gullies on a high-elevation south face in the South Colony area. 11/20/18 (full)
  • Widespread surface hoar formation around La Manga Pass (full)

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Avalanche Observations
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Field Reports
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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) Tue Dec 11 8:00 AM 25 29 16 80 26 2.0

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