• Backcountry Avalanche Forecast
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Tue, Dec 11, 2018 at 6:34 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

Recent skier-triggered avalanches illustrate the kind of avalanche you can trigger today. Storm snow over the weekend drifted into softer slabs below ridgelines,and in cross-loaded terrain features in the alpine. Strong westerly winds today should find any snow left available for transport and continue this modest loading on east-facing slopes. You can trigger a small avalanche like this one from Berthoud Pass today. A small avalanche can trigger larger avalanches breaking near the ground, like this one from St. Mary's Glacier. If a smaller avalanche steps down to more deeply buried weak layers, the avalanche will be much more dangerous and harder to escape.

Safer riding options include slopes sheltered from the wind, or slopes that face south and west that received much less recent wind-loading. 

 

Avalanche Problem

 
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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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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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Above Treeline
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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 11, 2018 at 4:08 AM by Brian Lazar Statewide Weather Forecast
  Tuesday Tuesday Night Wednesday
Temperature (ºF) 20 to 25 7 to 12 20 to 25
Wind Speed (mph) 20-30 G50 15-25 G50 18-28 G50
Wind Direction W W W
Sky Cover Mostly Cloudy Mostly Clear Mostly Cloudy
Snow (in) 0 to 1 0 1 to 3

Archived Forecasts

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Tue, Dec 11, 2018 at 7:32 AM
Issued by: Brian Lazar Statewide Weather Forecast  

People continue to trigger avalanches in the Northern Mountains. Yesterday a skier triggered an avalanche breaking up to 2 feet deep in the East Vail area, specifically Marvin's. The is steep east-facing terrain near and below treeline. Combine this fresh evidence with other obvious signs of instability like collapsing and shooting cracks and we get a clear picture of the problem we've been discussing for weeks: the threat of triggering a large and destructive avalanche breaking on weak layers buried by mid to late November snowfall. 

The storm snow over this past weekend added a modest load to these persistent weak layers. Strong westerly winds over the next couple days, combined with small amounts of new snow through Thursday will continue this pattern of incremental loading, most pronounced on east-facing terrain. It's easy to discount the impacts of seemingly innocuous amount of new and drifting snow, but even small amounts of incremental loading are notorious for keep persistent weak layers alive and active.

Yo'll be able to trigger small soft slabs around a foot or two deep in wind-loaded terrain. This problem will persist as long as snow continues to drift.

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 and entraining some serious mass. 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. 

This remote skier-triggered slide near Vail Pass occurred on west-facing terrain. So obviously not all west-facing terrain is safe, it's just that your much less likely to find the problem in this generally less wind-loaded aspect. 

Bottom line: 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)

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Avalanche Observations
Report Date # Elevation Aspect Type Trigger SizeR SizeD
View Sun Dec 9 - TL E - AM - D1
View Sat Dec 8 - TL E - AS - D2
View Sat Dec 8 - >TL E SS AS R2 D1.5
View Sat Dec 8 - TL E HS AS R2 D2

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Field Reports
Report Date Observer Snowpack Obs Avalanches Media
View Mon Dec 10 Grant Robbins No No No
View Mon Dec 10 Jason Konigsberg No No Yes (5)
View Sun Dec 9 Tyler Holmes No Yes (1) Yes (3)
View Sun Dec 9 Paul Rogers No No No
View Sun Dec 9 - No Yes (1) No
View Sun Dec 9 Kristopher Elyea No No No
View Sat Dec 8 - No Yes (1) Yes (2)
View Sat Dec 8 Morgan Scherrer No Yes (1) No

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Weather Observations
Station Date Time Temperature Relative Humidity Wind Speed Wind Direction Max Gust 24 Hr Snow
Bear Lake Tue Dec 11 7:00 AM 32 - - - - 1.0
Bottle Peak Tue Dec 11 6:50 AM 21 51 36 262 47 -
Berthoud Pass Tue Dec 11 7:00 AM 18 52 16 266 41 -
Cameron Pass Tue Dec 11 7:00 AM 20 40 9 213 18 -
Loveland Pass Tue Dec 11 7:00 AM 18 55 18 259 32 -
Joe Wright Tue Dec 11 6:00 AM 27 - - - - -
Loveland Basin Tue Dec 11 6:00 AM 23 - - - - -

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