Wind Slab formed in the past 24 hours is our primary avalanche problem, with older wind slabs from our recent successive storms adding complexity to the upper snowpack. Significant snowfall yesterday combined with westerly winds to transport significant snow into lee terrain and cross load other areas. The resulting wind slabs will vary in hardness and could be large. Expect them to be reactive to a trigger. Human triggered avalanches are very likely in High rated areas. Peak instability likely occurred last night, but we don’t expect these slabs have gained much strength since then. Two known close calls occurred yesterday, including a skier caught and carried in Gulf of Slides by an avalanche that occurred while the party ascended.  Shortly after, two skiers were knocked off of their feet at the base of Hillman’s Highway by a natural avalanche. The Hillman’s avalanche is a reminder that low angle areas in our terrain, especially the floor of Tuckerman Ravine, are in the runout of steeper terrain above and should be treated as avalanche terrain. Moving one at a time and carrying avalanche rescue gear is important.

This mix of scouring and deposition of new snow in the terrain makes natural avalanche activity unlikely but human triggered avalanches possible. Move one at a time today when poking into new snow and keep an eye on what or who is above or below you. Visibility will be challenging with flat light and snow showers making assessment and safe travel techniques more difficult. New wind slabs are likely to be largest in Lobster Claw and Right Gully and the northern gullies in Huntington due to their lee position. Hillman’s appears to have a more widely distributed 8″ (20cm) storm slab with less wind effect and fair to good stability. Be on the lookout for signs of wind transport in the afternoon as wind picks up to the 20-35mph range. Northwest winds tonight will ramp up into the range capable of building larger and more dangerous wind slabs. If you have weekend plans that include being in avalanche terrain, know that the forecast wind speed and direction will raise the avalanche danger tonight and tomorrow and build potentially touchy wind slabs in terrain downwind of a northwesterly.   

The old and icy snow surface we continue to talk about will be a key player as avalanche conditions develop from the incoming storm, with no deeper instabilities of concern. Slab building on a slick bed surface will likely occur in some areas while the old surface may remain exposed in others. We’re unsure at this time how well new snow will stick to the old surface for a variety of reasons. Slower wind speeds than might normally accompany a winter storm on Mount Washington could result in minimal scouring, but snow today will likely be light and easily transported by wind. Sluffing will also be a significant factor in slab development, as new snow may sluff off of the steepest portions of slide paths before slabs can build in these areas. These variables affecting slab development and distribution in our terrain will determine the number and size of avalanches we may see, with either many small avalanches or fewer large avalanches being potential outcomes of this storm cycle. Regardless, newly forming cohesive slabs should be reactive on the slick old snow serving as a bed surface.

Wind slab is scattered through the terrain. This initially formed Friday into Saturday and likely developed further thanks to snow that fell overnight. Areas of largest wind slab development are expected in Moderate rated areas due to being lee of prevailing NE winds, though wind slab may still be navigable by staying on old surface. While wind speed will be light by Mount Washington standards, the density of new snow (6% on the Summit and 7.7% at Hermit Lake) should still allow for wind transport and wind slab development in our terrain.

Areas of new wind slab are the primary avalanche problem though the primary hazard remains the potential for taking a high-speed sliding fall from steep terrain on the frozen, icy snowpack. Brief windows of visibility into Tuckerman Ravine have confirmed suspicions that much of yesterday’s new snow was scoured off of windward facing forecast zones by high winds from the east-northeast. The high wind speed and easterly direction coupled with very limited fetch, or area of available snow for transport, leads us to our low rating in most areas. Forecast areas that face due east contain much more limited areas of wind slab. These areas should be assessed carefully for sensitivity to human-triggering and consequences of being swept off your feet. More sheltered areas like the long northern gullies in Huntington and Lobster Claw and Right Gully in Tucks will likely harbor larger and harder to avoid wind slab. Human triggered wind slabs are possible where they have developed in steep terrain. Up to an inch of new snow today on continued NE wind will add slightly to existing wind slab.

Thin wind slabs, which formed earlier in the week, are scattered throughout northeast facing terrain. These have passed through their unstable phase and should not be of much concern except possibly in the very steepest locations. The old gray refrozen snowpack that makes up most of the travel surface in our forecast area, will be underfoot everywhere due to the thin coating of new snow on top. This surface will create the primary concern for climbing and riding due to its firm and icy nature. Any softening that occurs later in the day in the sun or with warming temperatures will likely be only at the surface. On days like today with temperatures around freezing, passing clouds can allow the snow to quickly refreeze and make arresting a fall difficult at best. Crampons, an ice axe and the ability to use them well will be useful to avoid a long sliding fall today.