This is the first significant warm-up in March and we expect this to complicate current avalanche conditions. Natural avalanche activity will be on the rise as the snowpack heats up. Check out the new Forecaster Blog on warming and the effects on our already complex snowpack
West to southwest wind has formed reactive wind slabs on leeward slopes. These could be triggered by the weight of a skier or rider, especially on east-northeast aspects.
Large looming cornices exist along ridgelines and require a wide berth from above and below, especially when they're baking in the sun.
Two layers of concern exist and have been reactive over the past couple of days. The upper layer being buried mid-February down 30-60 cm and has recently failed primarily on a sugary facet interface and the deeper layer of concern is found down 60-100 cm and consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine.
Wet loose avalanches are likely as the sun pokes out and freezing levels rise. Be observant as you travel, and look for signs of warming and snowpack instability. Snowballing, moist snow, and the most obvious is natural avalanche activity. Back off slopes and adjust your trip plan when things are heating up.
High pressure over the region will bring sunny skies and a significant warm-up. Freezing levels forecast 2000 m to 2500 m.
Wednesday: A mix of sun and cloud. Ridgetop wind light from the southwest. Alpine temperatures near 0 and freezing levels rising 1500-2000 m.
Thursday: Mostly sunny and ridgetop wind strong from the southwest. Alpine temperatures near + 3 and freezing levels 2000-2500 m.
Friday: Mostly sunny and ridgetop wind strong from the southwest. Alpine temperatures near + 2 and freezing levels 2000 -2500 m.
No recent avalanche reports on Tuesday.
Sun and warming is our primary concern over the next few days. Large looming cornices may weaken and fail, triggering slabs on the slopes below. Loose-wet avalanches will likely be seen from solar aspects first and then possibly all aspects. The persistent slab above the weak layers may stiffen and consolidate further, failing as a natural avalanche or becoming more sensitive to skier and rider triggers. This problem is not healing quickly and the conditions are not easily managed. A conservative mindset and patience are crucial right now.
Pockets of wind slab may be reactive on northeast-east aspects at upper elavtions.
Upper elevations are highly wind-affected and scouring down to rocks or crusts can be seen on west to southwest aspects. On leeward (northeast-east) slopes, stiff wind-slab has formed at treeline and in the alpine.
40 to 60 cm (in some places up to a meter) of snow now sits above sugary faceted snow that formed mid-February. Snowpack testing done by the South Rockies Field Team last Saturday in the Mear Lake area showed a relatively easy to moderate failure on the mid-Feb layer which propagated across the whole column (ECTP 13 down 40 cm). This test was on a south-facing slope at treeline and shows the sensitivity of this weak layer. Deeper in the snowpack (60 to 100 cm deep) is yet another weak layer that was buried at the end of January. This layer consists of surface hoar, faceted grains, and/or a hard melt-freeze crust. MIN reports prove these layers remain easily triggered by people.
Weak faceted grains and a decomposing melt-freeze crust can be found near the base of the snowpack.
The weather forecast is concerning with the current snowpack structure. Warming and solar radiation may stiffen and consolidate the slab above the weak layers. Expect surface snow to become moist and weak and large looming cornices overhead may fail, triggering slabs on the slopes below.
