This is an archived forecast related to a fatality on that day Issued on: Tue, Feb 18, 2025 at 4:30 PM Danger for Thursday, Feb 20 Above Treeline: 3 - Considerable Near and Below Treeline: 2 - Moderate You can trigger an avalanche on steep slopes at all elevations where recent snow has settled or drifted into a cohesive slab. The most dangerous slopes are above treeline and face northwest to north through southeast. Here, winds have drifted recent snow into deeper connected slabs, making larger avalanches more likely. Below treeline, warm temperatures will heat recent snow. You could trigger a loose avalanche where you sink up to your boot top in moist snow. Watch overhead for loose avalanches that start from steep rocky areas and gain mass as they move downhill. Avalanches may break broader and deeper than expected. Lower elevation slopes or slopes less than about 30 degrees in steepness offer safer travel options. Avalanche Problems (3) Problem: Persistent Slab Aspect/Elevation: W-N-E all elevations; SE and SW near and below treeline Likelihood: Possible Size: Small - Large 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. Problem: Wind Slab Aspect/Elevation: NW-NE-SE Above treeline Likelihood: Likely Size: Small - Large 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. Problem: Loose Wet Aspect/Elevation: W-S-E Below Treeline Likelihood: Possible Size: Small What you need to know about these avalanches: 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. Southern Mountains Regional Discussion What a storm! It is refreshing to see a fresh coat of snow painted on our mountain canvas. While snowfall is taking a break, weather changes carry on, and we expect to see warmer temperatures and northwest winds midweek. There is some uncertainty in how the recent storm slab is settling with recent weather changes. Reactivity is trending more stubborn, but the recent snow buried a shallow upper snowpack weak layer that may prove to linger as we move forward. Storm totals vary, but generally, 20 to 30 inches of snow fell, carrying 2 to 3 inches of snow water equivalent in most of the San Juan Mountains (sorry, La Garita's and Sangre de Cristo's). This bumped our snowpack back up to 75% of our 30-year average making a good rafting season slightly more attainable. We recorded 54 avalanches in the Southern Mountains in the last four days, with 20 slides triggered by humans. The bullseye aspect for avalanches was northeast-facing slopes at all elevations, with most slides breaking at the old snow/new snow interface. The storm snow is now settling into a slab, sitting over weak crusts and persistent grains on a variety of aspects. With no avalanches stepping down to the December drought layer, we are now most concerned with the surfaces buried by the recent snowfall, forming a new Persistent Slab avalanche problem. In areas that have been loaded or are actively loading with recent wind-drifted snow, we are most concerned with a higher sensitivity of a slab on this weak layer and avalanches breaking wider and deeper than expected. A natural avalanche in Battleship on Monday highlights this concern. Observers on Sunday reported a significant decrease in whumpfing and cracking with strong sunshine and warm temperatures producing as much as 5 inches of settlement. Warmer temperatures are yet to come. In the Southern San Juans, La Garaita's, and Sangre de Cristo Mountains, where recent snow fell on bare southern slopes at lower elevations, many slopes are burning out and threats of wet problems at lower elevations have, for the most part, already happened or are small and isolated. In the Northern San Juans where south slopes carried more snow and a stout melt-freeze crust prior to this storm, be on the lookout for wet slides that point release from rock bands and entrain recent snow as they move downhill. Continue to look for recent natural activity, cracking or collapsing, and unexpected changes in surface conditions. Each time you encounter something unexpected, it's a good time to stop and reevaluate your route plan before moving forward. Even if the snowpack seems complicated, the easy answer is terrain. Keeping your terrain choices to lower angled slopes that are not connected to steep slopes above gives you opportunities to enjoy the fresh snow stress-free.