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Thu, Dec 13, 2018 at 7:41 AM
Issued by: Spencer Logan

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.
  Danger Scale

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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 at higher elevations. Those slopes have the combination of widespread weak layers capped by thicker and stiffer slabs from lots of drifting snow. You can identify these slopes by looking for cornice growth above terrain features with smooth, pillowed fresh drifts. An inch or tow of snow on Wednesday will not change the danger.

You can reduce your risk by traveling on slopes less than 35 degrees. Safer riding options also include slopes sheltered from the wind, or slopes that face south and west that received much less recent wind-loading and where buried weak layers are not so prevalent. 

 

 

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
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 Thu, Dec 13, 2018 at 12:06 PM by Spencer Logan Statewide Weather Forecast
  Thursday Night Friday Friday Night
Temperature (ºF) 10 to 15 25 to 30 15 to 20
Wind Speed (mph) 10 to 20 5 to 15 10 to 20
Wind Direction NW W SW
Sky Cover Clear Clear Mostly Clear
Snow (in) 0 0 0

Archived Forecasts

  • Select Forecast: Valid

Thu, Dec 13, 2018 at 8:51 AM
Issued by: Chris Bilbrey Statewide Weather Forecast  

A north to south gradient in snow totals exists across the San Juan Mountains. The north side of Red Mountain Pass picked up over a foot of new snow while areas south of Red Mountain Pass and in the South San Juan zone received two to six inches. The Sangre de Cristo Range received only trace amounts of snow.

New snow and wind is adding additional stress to buried weak layers. With each loading event in December, numerous human-triggered avalanches were reported in the North San Juan zone on north through northeast to east-facing slopes. Almost all of the avalanches were failing on weak facets found mid-pack or near the ground and formed during dry weather periods in November.

Strong southwest winds prior to the storm shifted to north-northwest with the onset of snowfall, moving snow efficiently near and above treeline. These winds formed fresh, deeper drifts on southwest through southeast to northeast-facing slopes overnight. North and northwest-facing slopes that were loaded prior to snowfall were generally stripped back to the old snow surface.

In wind-loaded terrain, an avalanche you trigger near the surface could step down and break on facets buried deeper and entrain the entire season’s snowpack. Newly formed wind-drifts are overlapping our Persistent Slab avalanche problem on north to east-facing slopes above treeline. Identify wind-loaded terrain features of concern to reduce your risk to avalanches. Wind-drifts on southerly-facing slopes above a firm old snow surface will be easy to trigger from the weight of a rider and move fast.

Stick to slopes angles less than 35 degrees if stability is in question. The snow surface below treeline was very weak prior to the storm. Don’t let your guard down on steeper, treed terrain where new Storm Slabs up to six inches thick could fail on weak snow directly below. You may want to avoid steep slopes that end in terrain traps like gullies or large stands of trees.

 

 

 

 

 


  • 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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Five Day Trend

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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) Fri Dec 14 2:40 AM 18 39 - 120 4 1.0
Medano Pass Fri Dec 14 2:00 AM 13 - - - - -

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