Colorado Avalanche Information Center Bulletin
Issued on:Fri, Feb 24, 2023 at 4:30 PM
ARCHIVED - Related to two fatality incidents on 2/25 (both subject to this same advisory)

Above and Near Treeline: 3 - Considerable
Below Treeline: 2 - Moderate

The most dangerous areas are wind-loaded slopes. Southwest winds drifted the new snow into thicker slabs on northerly and easterly-facing slopes. Strong and erratic winds built dangerous drifts lower in the terrain than usual, and on wide open slopes below the treeline. Avalanches in the new snow could break into weaker snow layers three to four feet deep on slopes facing west through north to east. Avoid areas where you see evidence of recent wind drifting such as fresh cornices, rounded pillows of snow, or a hard, sculpted snow surface. If you experience cracking or collapsing, retreat to slopes around 30 degrees that are sheltered from the wind.

With a plethora of fresh snow on sunny slopes, Saturday's warm-up may trigger a shed cycle of the new snow from east through south to west-facing slopes during the day. Traveling on steeper slopes with about 8 inches of wet snow increases your chance to trigger a loose avalanche. Move to less steep slopes if you sink past your shins into wet snow or see fresh rollerball activity.

Avalanche Problems (3)

Problem: Wind Slab
Aspect/Elevation: NW-N-E-SE All Elevations
Likelihood: Likely
Size: Small - Large

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.

Problem: Persistent Slab
Aspect/Elevation: W-N-E Near and Above treeline
Likelihood: Possible
Size: Large

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.

Problem: Loose Wet
Aspect/Elevation W-S-E All Elevations
Likelihood: Likely
Size: Small - Large

Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

This information describes backcountry avalanche conditions within the specified forecast zone. It is a regional forecast and local conditions may vary, especially where there is an active avalanche hazard mitigation program.

Southern Mountains Regional Discussion

Snowfall started winding down around midday Friday across the western San Juan Mountains. Light snow continues for a couple more hours around Wolf Creek Pass before finally ceasing overnight. As a transient high-pressure ridge pushes toward Colorado Friday night, we get a brief respite from the wind. However, wind speeds remain elevated enough to transport the low-density new snow onto leeward slopes at upper elevations. Snowfall Thursday night delivered an additional three to seven inches in the North San Juan Mountains, five to fourteen inches in the South San Juan Mountains, and a couple of inches in the La Garita Mountains and Sangre de Cristo Range. Observers report between 30 and 40 inches of storm snow along the southern tier of the San Juan Mountains that do well on southwest flow.

Another moderate to significant new snow load aided by intense drifting has added stress to weak snow layers below. Wind-loaded slopes pose an increased threat to trigger an avalanche large enough to bury, injure or kill you. There's an outside chance that an avalanche triggered in the new snow could provoke a deeper failure in faceted snow grains buried around Valentine's Day and now under a three to four foot-thick cohesive slab. In the La Garita Mountains and Sangre de Cristo range, the snowpack as a whole is shallower and weaker. While snow totals there have been less, it will be easier to provoke a larger slide that takes out the entire snowpack in places with a thinner snowpack or where natural obstacles poke through the snow surface.

Most weather stations clocked sustained winds of 20 to 30 mph for several days during periods of heavy snowfall with gusts consistently between 70 and 80 mph, and isolated spots surpassed the 100 mph mark. When winds are this strong, terrain features and gullies create micro-eddy effects and can build thick, drifted slabs well below ridgelines and on atypical slopes. On the extreme end, the new snow may have been sublimated back into the atmosphere never landing on leeward slopes. Regardless, observers report numerous wind-affected slopes at all elevations. Erratic wind directions also make it more challenging to know with certainty prominent drifting patterns.

Field observations have reported generally good bonding to various old snow surfaces under the new snow but also identified several stubborn to reactive storm layers in snowpack tests. Without fragile snow grains immediately below the new snow, it may take a wind-thickened slab or slightly steeper slope to provoke an avalanche. Dig down to investigate sensitivity of storm layers versus blindly charging into steeper terrain - especially in places with about a foot or more of fresh snow. Use surface clues to identify areas that may harbor thicker, more dangerous wind-drifted slabs and choose an alternative route with a safe exit strategy if you experience signs of unstable snow.

As temperatures climb above the freezing mark Saturday under partly to mostly sunny skies, loose avalanche activity will likely occur along the southern half of the compass. With a firm crust below the new snow on east through south to west aspects, wet sluffs can potentially travel faster and farther than you anticipate. Be ahead of the surface warming curve that occurs first on easterly slopes tracking west during the day. Limit travel on or below slopes where you find a wet, sticky snow surface or retreat to shadier slopes.