This information was published 03/02/2020 at 6:53 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Areas of wind drifted snow are the locations that will be possible to trigger an avalanche today. You can reduce your hazard by sticking to scoured slopes. Evaluate snow carefully today. If you decide to move through softer snow on foot or skis, traveling one at a time and identifying features of concern will help make travel safer. MODERATE avalanche danger exists today due to the possibility of human triggered avalanches.
Yesterday, under half an inch of snow fell on Mount Washington while wind from NW blew 40-60mph for the day. The temperature climbed steadily overnight from 0F to a current mid-teens F.
Today, temperatures will continue to rise, possibly maxing for the day early afternoon. It appears as if above 3500’ will stay below freezing, though even the summit will reach close to 30F today. Up to an inch of snow is forecast by midnight tonight, with mixed forms falling at lower elevations. Monday morning wind at 40moph from the west should increase to 75 mph later today.
Tomorrow will be clear with mild wind from the W and warm temperatures. It seems likely above 5500’ will stay below freezing. Our mid elevation band may and the lower elevations likely will see temperatures in the mid-30sF. Precipitation on Tuesday should hold off until after dark with 3-5” forecast on the summit.
Primary Avalanche Problem – Wind Slab
Avalanche terrain contains both stubborn and reactive wind slabs. The easiest way to discern between the two is stubborn areas will be firm and supportive to booting while reactive areas should be softer and will likely lure skiers. Over an inch of snow Friday and again Saturday with continued loading wind speeds from the W created constant wind loading in Tuckerman yesterday. Cross-loaded slopes may contain reactive snow on one side of the avalanche path with stubborn wind slab on the other. Identifying which specific terrain features contain softer snow will aid in traveling through terrain today.
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.
Following our big storm last week, we have since seen an inch or two of new snow each day combining with wind from the W and NW that blew from 30-65mph. Mild speeds by Mount Washington standards; this has created the mix of stubborn and reactive wind slabs that you’ll find today rather than our classic windboard and sastrugi. Many slopes contain a mix of soft and firm wind slabs that will put the decision-making squarely on your group to figure out how to manage this mix of sensitivity.
Rapid warming is a red flag and while we will see temperatures warm today, we believe a number of factors will keep the degree of instability this introduces to a minimum. Max temperatures are forecast for mid-afternoon and should stay below freezing above 3500’. Cloud cover will keep ambient air as the driver of warming and lessen, if not eliminate, solar gain. Wind slabs that could see decreased stability are fairly thick, meaning it would take significant warming to affect, much more than we should see today. Warming wind slabs always introduce a degree of uncertainty, but if today’s weather forecast plays out accurately, we believe warming should not play much of a factor today. If the weather changes from forecast such as clearing skies, earlier warming, or rain rather than snow flurries, we may see a decrease in stability or isolated wet loose activity at lower elevations, though likely still fitting within a Moderate rating.
The Sherburne and Gulf of Slides ski trails are covered with soft snow to Pinkham Notch.
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. Clickhere to check it out.
Recent snowpack and avalanche observations can be foundhere and on Instagram. Your observations help improve our forecast product. Please take a moment andsubmit 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 03/02/2020 at 6:53 AM.
USDA Forest Service
White Mountain National Forest
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