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Sun, Apr 18, 2021 at 7:30 AM
Issued by: Spencer Logan

Sunday

 

Monday

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

With the sun hitting the recent snow today, expect some small Loose Wet Avalanche activity. Rollerballs and snow falling from rocks are early indicators of surface warming. Move to more northerly slopes with colder surface snow to avoid these conditions. Cornices have started to droop with warm temperatures in April, as temperatures rise, give them extra room while traveling along or under steep ridges.

You could trigger small avalanches that break in the new snow on steep alpine slopes today. These slides will only be dangerous if you are knocked off your feet or machine above trees, rocks, or cliffs. Look for smooth, rounded snow surfaces to help identify these areas of potential danger.

 

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


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


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.

Weather Forecast for 11,000ft Issued Sun, Apr 18, 2021 at 12:17 PM by Spencer Logan Statewide Weather Forecast
  Sunday Night Monday Monday Night
Temperature (ºF) 15 to 20 35 to 40 5 to 10
Wind Speed (mph) 5 to 15 15 to 25 15 to 25
Wind Direction WSW W NW
Sky Cover Mostly Clear Increasing Mostly Cloudy
Snow (in) 0 0 to 1 0 to 3

Archived Forecasts

  • Select Forecast: Valid

Sun, Apr 18, 2021 at 6:48 AM
Issued by: Becs Hodgetts Statewide Weather Forecast  

Without strong winds to drive Wind Slab formation, new snow amounts totaling 2 to 6 inches were not enough to raise the avalanche danger in the North and South San Juan, however up to 10 inches of new snow raises the hazard in the Sangres. CAIC forecasters Friday reported good bonding at the new/ old snow interface and right-side-up storm snow that fell Thursday night and earlier in the week. Although any wind-deposited slabs will be small and manageable, approach slopes over 35 degrees with caution if you encounter new snow amounts or drifts that exceed 10 inches.

Once the sun hits slopes today, expect natural sluffing from steep slopes, rockbands, and cliffs. Avoid traveling above cliffs or consequential terrain if you observe fresh rollerballs or pinwheels In the past, backcountry travelers have been caught off guard when accidentally triggering a small pocket of wind-drifted snow in steep terrain and getting swept down the mountain. You are more likely to trigger a small avalanche where the new snow fell onto a firm old snow surface or crust.

Large, sagging cornices dot the landscape. As you travel along ridgetops, give these beasts a wide berth, as they often break further back onto flatter terrain than you might expect. Recently, the forecast staff has observed cornices pulling away from the rock and creating motes. Although we have no reports of cornice failures in our zone, they are unpredictable and can cave off during peak daytime heating. The worst-case scenario is a large cornice failure triggering a deeper avalanche where weak snow lingers near the ground on northerly above treeline slopes.


  • Keep an eye out for shallow, soft slabs of wind-deposited snow on north, northeast, and east-facing slopes in the alpine. Newly formed slabs, identified by their smooth, rounded appearance will be deeper below ridges, at the top of steep chutes, or in cross-loaded terrain features. South San Juan. 4/14/21. (full)
  • This loose dry sluff triggered a slab avalanche while moving down the slope on Parrot Peak. This slide occurred on a north aspect and traveled close to 1,000 feet down the slope. South San Juan. 3/26/21. (full)
  • Cornice fall from a few days ago on a North aspect. North San Juan. April 2, 2021. (full)
  • Two wind slab avalanches that naturally ran on Monday on a northeast aspect. March 29, 2021 NSJ (full)

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Weather Observations
Station Date Time Temperature Relative Humidity Wind Speed Wind Direction Max Gust 24 Hr Snow
Hayden Pass Sun Apr 18 8:00 PM 26 - - - - -

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