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Saturday, November 17, 2018 at 9:41 AM Issued by: Spencer Logan  

This is the last Statewide update for 2018. Zone-specific backcountry avalanche forecasts begin tomorrow (11/15). Zone forecasts are published every day by 8 AM through the spring. 

The primary avalanche concern is that a backcountry rider can trigger a large avalanche that breaks on weak, collapsible snow layers near the ground. This problem is specific to northerly and east-facing terrain where a harder wind-drifted slabs sits on top of worrisome weak layers. The only way to avoid this issue is to avoid the above-mentioned slopes. Sheltered areas and southerly-facing slopes are relatively safe from these Persistent Slab avalanches.

In the past couple weeks riders have triggered numerous large and dangerous avalanches. A large number of these avalanches were in the Northern Mountains. Although this is where the majority of avalanche activity has been, large avalanches were reported from all over the state including the San Juan mountains. The avalanche danger is greatest in the Northern Mountains, especially the Front Range, as northern and eastern areas received the most recent snow. As you move south through the state, the avalanche danger tapers, but as recent avalanche activity shows, large avalanches can be triggered on wind-loaded slopes in any mountain range in Colorado.

If you are traveling on south-facing slopes be aware that the northerly wind of the last few days drifted snow into slabs on these sunny slopes. It will possible to trigger small avalanches in this wind-drifted snow. Wind Slab avalanches can be avoided by steering clear of areas of snow near ridgetop or on the walls of gully-features that feel hard and have a smooth looking appearance. Hollow sounding snow underfoot or machine is also a sign that you may be traveling on one of these slabs.

As the dry weather pattern continues, overall snowpack stability increases. Avalanches are harder to trigger and the amount of slopes where you can trigger an avalanche decrease. This doesn't mean avalanches are impossible and if you head for a wind-loaded northerly and east-facing slope, there is a chance you can trigger a large and dangerous avalanche.

The clear and cold weather is changing our snowpack and increasing the snowpack stability by weakening surface slabs. This is good for short-term stability but not a good weather pattern for our snowpack in the longer term. Under this weather regime weak layers will continue to flourish, both near the ground and near the surface, and our next major snow storm will once again lead to widespread avalanche activity.

 

 

 
  • This chart shows avalanche activity in Colorado for the first two weeks of November. There is a clear trend of more activity in the north and less as you head south in the state. (full)
  • Stability is increasing throughout much of Colorado. But it is still possible to trigger an avalanche. Northerly and east-facing slopes have a layered and poor snowpack structure. Wind-loaded slopes are most dangerous as this where the slab is the thickest over the weak snow layers.
  • This avalanche distribution rose shows avalanche activity in Colorado from November 1 to November 14, 2018. The highlighted areas are where the most activity has occurred. This is where wind-drifted slabs rest on top of weak, collapsible layers of snow. (full)
  • Test results on this northeast-facing slope indicate stability but the structure of the snowpack indicates future problems on this slopes and current problems where there is more of a slab. (full)
  • A large avalanche was remotely triggered by a skier on Peak 1 near Breckenridge (11/8). This slope is northeast-facing and wind-loaded. The skiers were descending the ridge and had no intention of skiing the slope that slid. Even so, the crown of the avalanche was within 5 feet of their up-track. (full)
  • Northeast and east-facing slopes near Marble. The red circles indicate isolated wind-drifted areas where you might be able to trigger a slab avalanche breaking on a buried crusts about 30cm deep. 11.12.18 (full)
  • quick synopsis of snow layering at 11,400ft on South Diamond Peak on recent D1.5 windslab crown. This is near Cameron Pass in the Front Range. 11/11/18 (full)

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Avalanche Observations
Report Date # Elevation Aspect Type Trigger SizeR SizeD
View Thu Dec 13 - >TL NE WS N R2 D2
View Thu Dec 13 - TL E WS N R2 D2
View Thu Dec 13 - TL E SS U R2 D2
View Thu Dec 13 - >TL NW SS N / u R2 D2
View Thu Dec 13 - >TL NE SS N / u R2 D2.5
View Thu Dec 13 - >TL SE - N R1 D1
View Thu Dec 13 - >TL E - N R1 D1
View Thu Dec 13 - >TL SE SS N R1 D1.5
View Thu Dec 13 - >TL NE HS N / u R2 D2
View Thu Dec 13 - TL NE SS N R2 D2

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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 Nolan Averbuch No No No
View Thu Dec 13 David Pfeiffer No No Yes (1)
View Thu Dec 13 john morrone No No Yes (1)
View Thu Dec 13 - No No No
View Thu Dec 13 Chris Bilbrey No Yes (2) Yes (5)
View Thu Dec 13 Kreston Rohrig No No Yes (2)
View Thu Dec 13 Ryan Zarter No Yes (1) Yes (1)
View Thu Dec 13 Jeff Davis No Yes (1) Yes (3)
View Thu Dec 13 Jeff Davis Ann Mellick No Yes (3) Yes (5)

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Weather Observations
Station Date Time Temperature Relative Humidity Wind Speed Wind Direction Max Gust 24 Hr Snow
Bear Lake Fri Dec 14 2:00 AM 27 - - - - 3.0
Steamboat Lake State Park Fri Dec 14 3:00 AM -3 90 1 134 3 -
Bottle Peak Fri Dec 14 2:50 AM 19 56 7 282 8 -
Berthoud Pass Fri Dec 14 3:00 AM 16 59 7 19 12 -
Cameron Pass Fri Dec 14 3:00 AM 16 83 7 227 12 -
Cottonwood Pass Fri Dec 14 3:00 AM 19 38 12 289 18 0.2
Kendall Mt Fri Dec 14 2:00 AM 21 19 15 10 18 -
Loveland Pass Fri Dec 14 2:00 AM 18 57 9 303 20 -
Molas Pass Fri Dec 14 3:00 AM 18 41 2 242 4 0.2
Putney Fri Dec 14 3:00 AM 23 22 6 4 9 -
Swamp Angel Fri Dec 14 3:00 AM 15 59 2 253 3 -
Vail Pass - Cdot Yard Fri Dec 14 3:00 AM 9 93 1 86 2 0.2
Monarch Pass (050e200) Fri Dec 14 3:04 AM 14 49 9 195 13 -
Columbus Basin Fri Dec 14 1:00 AM 24 - - - - -
Lizard Head Pass Fri Dec 14 1:00 AM 11 - - - - -
Medano Pass Fri Dec 14 2:00 AM 13 - - - - -
Mesa Lakes Fri Dec 14 2:00 AM 18 - - - - -
Ripple Creek Fri Dec 14 1:00 AM 14 - 0 75 - -
Slumgullion Fri Dec 14 1:00 AM 21 - - - - -
Schofield Pass Fri Dec 14 2:00 AM 12 - - - - -
Storm Peak Observatory Fri Dec 14 1:50 AM 13 59 8 251 9 -
Taylor Park Fri Dec 14 1:57 AM 8 62 3 329 4 -
Wolf Creek Summit Fri Dec 14 1:00 AM 26 - - - - -
Zirkel Fri Dec 14 1:00 AM 8 - - - - -

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