Avalanche Forecast for Saturday, February 22, 2020
This information was published 02/22/2020 at 7:02 AM.
The Bottom Line
Avalanche conditions are generally safe. That being said, LOW avalanche danger today does not mean no avalanche danger, nor does it reduce the other objective hazards associated with traveling in the mountains. If traveling or riding in extreme terrain, consider the consequences of triggering even a small slide or losing an edge on the firm snow while skiing and where a fall or slide might take you. Losing control in very steep terrain can lead to unfortunate outcomes if you slam into rocks, careen into other people, or go over a cliff. Practicing safe travel habits like continuing to carry avalanche rescue gear, traveling one at a time, choosing a slope appropriate for your skill level, and choosing an objective based on where the crowds ARE NOT, will help make today one to remember.
Yesterday was clear with no new snow nor observed wind transport. The day started with most elevations below 0F and ended about 20 degrees warmer.
Today begins with clear skies, a summit temperature of 2F and wind from the west blowing 60-70mph. Temperatures should warm to the teens F on the summit and the high 20sF below 3500’. Wind will decrease slightly. Afternoon snow flurries may bring a trace of snow to mid and upper elevations.
Tomorrow will get warm, though above 3500’ looks to stay below freezing. Skies will be clear with wind from the west around 30mph.
Primary Avalanche Problem – Wind Slab
The last reported avalanche occurred mid-week during a direct-action natural cycle that ran primarily on N, NE, and E aspects. Since then, wind has blown hard and left us with the unreactive wind slabs that you’ll find today. This wind slab is smooth and firm, primarily pencil hard with one-step softer layers beneath. Triggering these wind slabs are unlikely, though not impossible; you might find protected areas with softer snow or where the wind slab becomes thin, though these are isolated pockets. The largest wind slabs are mostly hard and unreactive and you can further reduce the unlikely risk of triggering by not overloading the slope with multiple people.
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.
Observations yesterday from the Presidential Range confirmed suspicions about what 18 hours of wind in the 70-90mph range can do to several inches of new snow. Windward slopes are now scoured to ice crusts or occasional patches of sastrugi and lack today’s wind slab problem. Lee slopes have thick, hard, wind slab that exhibit a slight upside-down structure and no propagation.
Forecast “in the clear under sunny skies” and the weekend may lead you to lesser known destinations to escape the crowd. These will exhibit the wind slab issues, but here’s another find from the field yesterday that is worth tucking in your back pocket. Thanks to the wind, we’re seeing the Feb 6/7 ice crust exposed in places. Cold weather this past week has promoted the development of facets under this crust. This faceting is likely not an issue where wind slab is thick or where avalanche cycles have broken the crust up. This leaves southerly aspects or perhaps less extreme terrain that did not get loaded or avalanche during the past week. These are candidates to harbor facet development. Encountering these facets may not alter your plans, but it’s another proof that Low does not mean no avalanche danger.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch and are skiing just fine.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit a photo or two and a brief description of snow and avalanche information that you gather in the field.
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 02/22/2020 at 7:02 AM.
USDA Forest Service
White Mountain National Forest