Colorado Front Range Archived Backcountry Avalanche Forecast Forecast Discussion Sat, Jan 16, 2016 at 7:24 AM Issued by: Jason Konigsberg Today, Tomorrow, Above Treeline Moderate (2) - Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully. Today, Tomorrow, Below Treeline Low (1) - Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Summary The series of storms continue with most of the Front Range picking up an additional 3 to 6 inches of snow overnight. The one thing constant throughout the zone is the wind. Strong west to northwest winds continue to drift snow onto northeast to east through south aspects. The wind-drifted snow is being deposited onto a weak snow surface which will make the drifts sensitive to the weight of a rider. Avoid areas of wind-drifted snow, especially if you see obvious signs of instability such as shooting cracks underneath of you. The wind and new snow from last weekend caused sensitive Wind Slab avalanche conditions. The new snow and wind from the last two days is falling on the same snow surface so we would expect similar results. It is also important to keep in mind that a relatively small Wind Slab avalanche has potential to step down to more deeply buried weak layers in the snowpack resulting in a large Persistent Slab avalanche. Even though snow amounts are on the lower end it sometimes does not take a lot to reactivate a Persistent Slab avalanche problem. There was recent avalanche activity on Tuesday with a remotely triggered avalanche that broke near the ground on a northeast aspect. The Persistent Slab avalanche problem is far from gone so we need to continue to evaluate snow and terrain carefully. Likely places where you can find this avalanche problem are on steep slopes that are very rocky and unsupported. Avalanche Problem - Wind Slab Where: NE - S Above and Near Treeline Probability: Possible Size: Small 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 - Persistent Slab Where: N - Se Above and Near Treeline Probability: Possible Size: Small - 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. Forecast Discussion Sat, Jan 16, 2016 at 9:47 AM Issued by: Jason Konigsberg A large amount of uncertainty currently revolves around our statewide Persistent Slab avalanche p roblem. Uncertainty exists because of a wide variability in our snowpack right now. The variability is not purely geographic so it is hard to group differences into something like north, central, and south. We can group the snowpack into three categories, but the trouble lies in where exactly the distribution of these categories lie. On one side of the spectrum, we have a completely faceted snowpack with no slab and no current problem. On the other side of the spectrum, we have a deeper snowpack that seems to be strengthening. It is also difficult, but not impossible, for a rider to affect layers buried more than two meters deep. Then there is the middle category, which is the trickiest. The middle category is a snowpack that has a Persistent Slab structure, a cohesive slab overlying weak snow, and a snow depth that is in the 1 to 1.5 meter range. The Crested Butte Avalanche Center does a great job of describing these three categories in this video. This middle category is tricky because we know the weak layer is well within the range that riders effect, yet we are not seeing many avalanches breaking on buried persistent weak layers. It is also tricky because it is difficult to nail down exactly where this structure exists. It seems to live near treeline but we cannot say that for sure and most of us don't go around recreating in the mountains constantly probing and measuring the snowpack depth. The only thing we can do to mitigate this uncertainty is to give this Persistent Avalanche problem a wide buffer. This is especially important every time there is a loading event no matter how small. A good example of how small loads can reactivate a Persistent Slab avalanche problem is in this video from Montana. The snowpack in other states is generally weaker right now but we have seen similar incidents in Colorado in the past after small loading events. If you have been recreating in and around steep terrain, now is a good time to take a step back, reevaluate the problem, and see if the new snow and wind will change the situation. In all zones, there is snow available for transport and strong winds are drifting snow into slabs on lee slopes. The Wind Slab avalanche problem is its own issue and should be considered. But will a small Wind Slab avalanche contribute to a deeper avalanche? We do not know the answer to this question so the best practice for reducing risk to avalanches at this time is to be patient. After this series of storms is over we will filter through observations and reported avalanches and we will hopefully have a better idea of the sensitivity, likelihood of triggering, and distribution of our Persistent Slab avalanche problem.