Avalanche Forecast for Tuesday, January 15, 2019
This information was published 01/15/2019 at 6:57 AM.
The Bottom Line
Varied snow surface conditions are generally quite firm or scoured to old crusts, and you’re unlikely to trigger an avalanche in these layers. Keep your eyes open for softer pockets of snow which may hold lingering stability concerns. The variable conditions make both crampons and avalanche rescue gear appropriate for today. Visibility may challenge your ability to judge the snow surfaces you plan to travel on. All forecast areas have LOW avalanche danger. Do continue to look for unstable snow on isolated terrain features.
A high temperatures of 21F, clear skies, and light winds yesterday has given way to increasing NW wind and partial cloud cover. Partially to mostly cloudy skies should persist through today with a slight chance of snow flurries producing no measurable precipitation. Temperatures will be a few degrees colder than yesterday, but still remain in the teens F for daylight hours. The current NW wind of 47 mph on the summit will decrease slightly through today and shift W tonight before ramping up towards 70 mph tomorrow. A fast moving storm tomorrow may bring a few inches of snow.
Primary Avalanche Problem – Wind Slab
Hard wind slabs which are quite large in some terrain should be unreactive to a human trigger. Still, on the off chance that you find a weak point in one of those slabs, it’s worth treating them with respect. Smaller pockets of softer slabs can also be found in the alpine, particularly on S and SE aspects where some of the largest hard slabs also exist. These softer pockets of wind slab are likely stubborn to a human trigger. You probably won’t trigger an avalanche today, but it’s not the kind of Low avalanche danger that provides truly green light conditions.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Field time and observations through much of the central presidential range has illustrated an interesting pattern of wind loading and scouring from last week’s storm. Terrain lacking a significant upwind fetch area for loading on a NW wind, like Huntington Ravine and the Great Gulf, experienced as much or more scouring than loading last week. Areas of December 22 crust are exposed and wind slabs are generally small. Oppositely, terrain with a significant fetch zone for a NW wind, like Tuckerman Ravine, Gulf of Slides, and Oakes Gulf experienced a great deal of wind loading and corresponding large avalanche activity. In most locations, wind slab formed late last week is hard and unreactive to a human trigger. The current conditions show that when wind is the primary driver of snowpack development, similar aspects and elevations in relatively close proximity do not always mirror each other. Another key characteristic of our snowpack is the December 22 rain crust. We think a number of avalanches last week ran on this robust and fairly smooth crust as a bed surface, and it may continue to act as a bed surface for future avalanches. You will also likely find this crust as the dominant snow surface in middle and upper elevation Westerly terrain where the avalanche problem is absent.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
Safe travel in avalanche terrain requires training and experience. This forecast is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 01/15/2019 at 6:57 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest