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Thu, Dec 13, 2018 at 7:31 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 could trigger a dangerous avalanche breaking on buried weak layers today. North and east-facing slopes at higher elevations are most dangerous since they have the combination of widespread weak layers capped by thicker and stiffer slabs. Observers are still reporting large collapses, indicating that that you can trigger a dangerous avalanche. A bit more snow and strong westerly winds will add more drifting snow to these slopes today.

You can trigger avalanches in newly-formed, wind-drifted slabs today. Strong west to northwest winds associated with the new snow has continued to build thicker and thicker slabs of drifted snow on northeast to east to southeast facing slopes. You will find them below ridge lines and down wind of terrain features. These slabs are stacked on top of the troubling weak layers, and a small avalanche in the surface snow could trigger a large and destructive slide breaking closer to the ground. 

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
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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


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

 
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


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

Archived Forecasts

  • Select Forecast: Valid

Thu, Dec 13, 2018 at 7:29 AM
Issued by: Kreston Rohrig Statewide Weather Forecast  

The avalanche danger has elevated to Considerable (level3) in the Steamboat and Flat Tops zone but should include areas around Cameron Pass as well. Accumulations of up to 10 inches of new snow will increase the likelihood for you to trigger and get caught in an avalanche today. In many areas across the northern mountains the new snow has fallen on a mixed bag of weak snow surfaces. 

The more serious concern is that a small avalanche may have enough mass to trigger the more deeply buried weak layers. These avalanches are now breaking 4 to 5 feet deep. Even without a small avalanche in the surface snow, you can trigger one of these Persistent Slab avalanches all by yourself if you find the wrong spot. These are localized shallow spots in the snowpack, like along slab margins, and in rocky areas. avoid these and reduce your risk. 

Ongoing reports of weak snow and human-triggered avalanches are clear evidence of these looming problems. Observers reported collapsing in the Winter Park and Byers Peak areas of the Front Range. In the Butler Gulch area, observers reported ECT's failing upon isolation on near-treeline east-facing terrain. Over in East Vail, a skier triggered this slide on steep northeast facing slope on Monday. And up in Steamboat, were getting reports of collapsing and worrisome snowpack results.

That's pretty solid and widespread evidence that the threat of triggering a large and destructive avalanche breaking on persistent weak layers buried by mid to late November snowfall is alive and well.

For the near future north and east-facing terrain is most dangerous. Stiffer, thicker, and more continuous slabs overlying more widespread weak layers. But don't let your guard down on other aspects. If the slope looks wind-loaded, or you can see the snowcover spanning enough terrain that a large slab is possible, check and see if there are buried weak layers under a stiffer slab before venturing into steeper terrain. 


  • Large skier-triggered avalanche at St Mary's Glacier 12.8.18. East aspects in the alpine. This avalanche broke up to 4 feet deep (full)
  • Large skier-triggered avalanche at St Mary's Glacier 12.8.18. East aspects in the alpine. This avalanche broke up to 4 feet deep (full)
  • Remotely skier-triggered avalanche in Uneva Bow near Vail Pass The crown was up to 4 feet deep. 12.9.18. (full)

See more photos & videos

Five Day Trend

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Avalanche Observations
No relevant backcountry observations found for this forecast

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Field Reports
Report Date Observer Snowpack Obs Avalanches Media
View Thu Dec 13 Paul Rogers No No No
View Thu Dec 13 David Pfeiffer No No Yes (1)
View Thu Dec 13 john morrone No No Yes (1)
View Wed Dec 12 Spencer Logan No No No
View Tue Dec 11 - No No Yes (1)
View Tue Dec 11 Banning Starr Yes (1) No Yes (2)

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Weather Observations
Station Date Time Temperature Relative Humidity Wind Speed Wind Direction Max Gust 24 Hr Snow
Bottle Peak Fri Dec 14 1:50 AM 19 55 8 268 10 1.0
Berthoud Pass Fri Dec 14 2:00 AM 16 60 9 349 18 -
Cameron Pass Fri Dec 14 2:00 AM 13 87 8 189 14 -
Loveland Pass Fri Dec 14 1:00 AM 17 55 6 134 16 -

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