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Fri, Jan 17, 2020 at 7:05 AM
Issued by: Jason Konigsberg

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

Snow and wind today will create new slabs of drifted snow on easterly slopes. Avalanches will be mostly small in the new snow. The biggest consequence of these new wind deposits is that they mask a deeper and larger problem. Drifted snow will land on harder and thicker slabs which sit over weaker, softer and collapsible snow layers. With this snowpack setup, any small avalanche you trigger in the new snow can result in a much larger and more dangerous avalanche.

To lower your risk to avalanches today, avoid steep slopes that are receiving drifted snow. Even if you don't see active wind loading, avoid areas that were loaded over the past week. These slopes are harder to identify but they will most likely face an easterly direction and they are located directly below ridgetop. Stick to sheltered areas to find relatively safer conditions.

 

Avalanche Problem

 
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N
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SW
Above Treeline
Near Treeline
Below Treeline
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Possible
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Historic
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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


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 Fri, Jan 17, 2020 at 12:40 PM by Jason Konigsberg Statewide Weather Forecast
  Friday Night Saturday Saturday Night
Temperature (ºF) 0 to 5 17 to 22 8 to 13
Wind Speed (mph) 15 to 25 15 to 25 12 to 22
Wind Direction WSW WSW WSW
Sky Cover Mostly Clear Partly Cloudy Mostly Cloudy
Snow (in) 0 0 0

Archived Forecasts

  • Select Forecast: Valid

Fri, Jan 17, 2020 at 8:09 AM
Issued by: Chris Bilbrey Statewide Weather Forecast  

Phase one of a two-phase storm system passed to our south and east overnight. Light snowfall and strong south to southwest winds built fresh, shallow surfaces slabs throughout the Southern Mountains. Generally, one to two inches of new snow is reported with up to four inches on Wolf Creek Pass. An additional three to five inches of snow is possible today before the storm quickly exists to the east. The next round of precipitation comes with a bump in wind speeds from a cold front this afternoon contributing to more blowing and drifting snow.

This new, light load should not overload and tip the scale on the generally strong snowpack in the San Juan Mountains. Smaller snowfall totals in the Sangre de Cristo range means no change to the avalanche danger for today, but an overall shallower, weak snowpack structure exists there. With each strong wind-loading event during January in the San Juan Mountains, we’ve seen natural avalanches popping in the alpine – be on the lookout for similar conditions today and tomorrow.

The most obvious and easier to manage avalanche problem today is newly formed wind-drifted slabs on leeward slopes. Thickest and potentially more reactive drifts are found in areas that received the most snowfall – the South San Juan zone favoring the eastern side. These fresh slabs formed above a variety of old snow surfaces such as wind-stiffened alpine surfaces, thin melt-freeze crust on sunny slopes, and decomposing fragments/ near-surface facets on shady slopes. New snow densities around 10% may promote good bonding with firm surfaces but the new snow may be easier to trigger where softer snow is found below. Denser snow increases slab strength and this may allow it to rest above weaker snow waiting for an extra push from a rider or machine before avalanching. On the flip side, a more cohesive slab has potential to break wide than expected, run farther, and entrain more snow leading to a larger, more violent avalanche.

Continue to use caution on slopes facing east, southeast, and south at higher elevations. Since January 1st, the largest proportion of natural avalanches have occurred on those aspects (49 out of 72) in the North and South San Juan zones. Although rider-triggering on those same aspects has been limited, a rider in the North San Juan zone on Tuesday triggered a large avalanche near treeline on a southeast-facing slope. This avalanche is bulls-eye information that our Persistent Slab avalanche problem may be coming back into play near treeline in more areas. A series of buried crust/ facet combinations as well as lingering depth hoar remain along with an overall shallower snowpack. Slopes with overlapping Wind Slab and Persistent Slab avalanche problems have potential for a shallow slide to step down into deeper weak layers producing a more dangerous slide that would be difficult to survive.

Northwest aspects still remain the most concerning of north-facing terrain due to more scouring and loading. This has contributed to highly variable snow depth and overall snow cover. Shallower areas with weak, faceted, cohesionless snow may have stiffer snow above making for a complex pattern. Managing your terrain selection is key to avoiding an avalanche encounter today and strive to avoid likely trigger locations such as the edge of the slab or near rocky outcrops.


  • Upper Bear Creek wind loading. January 14, 2020. (full)
  • E aspect, alpine from cross loading wind. (full)
  • Reactive storm snow below ridgelines on an east aspect at treeline. These slides were soft, relatively small, and generally harmless. Slides of this nature in steeper, bigger terrain could entrain enough snow to potentially bury a person. South San Juan. January 13, 2019. (full)
  • Strong winds have scoured west and southwest aspects in the alpine. Deeper snow depths exists in leeward terrain. Lewis Mountain, South San Juan zone. January 13, 2019. (full)

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Weather Observations
Station Date Time Temperature Relative Humidity Wind Speed Wind Direction Max Gust 24 Hr Snow
Medano Pass Sat Jan 18 2:00 AM 21 - - - - -
South Colony Sat Jan 18 1:00 AM 22 - 3 246 - 3.0

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