This information was published 02/04/2020 at 7:11 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Human triggered avalanches are possible today where wind carried and deposited recent snow. Watch for fresh slabs of wind drifting snow on steep slopes and cross loaded gullies in eastern ravines above 3500’.
The chance for new snow today will result in conditions changing by the hour, and decreased visibility: watch for snowpack instability clues continuously. Today’s avalanche hazard rating is MODERATE.
Yesterday the summit of Mt Washington recorded 1.8” of new snow and just a trace at Hermit Lake. Wind from the WNW at 60-80mph through the day decreased after midnight to 50 mph. Temperatures remained in the lower teens.
Today, snow showers late morning and afternoon may bring another trace to 2” of snow, with W wind at 35-55. Temperatures will reach the lower 20sF.
Looking ahead, clear skies and single digits F for Wednesday and a trace to 2” of snow Wednesday night and Thursday morning.
Primary Avalanche Problem – Wind Slab
Slabs of wind drifted snow are the main avalanche problem to look for today, and are easy to visually identify making them easy to avoid. Hotspots for these wind slabs are areas with the most upwind fetch, this includes most of the Tuckerman Ravine Headwall, and the major gullies in the Gulf of Slides. Possible new snow today on a west wind will build new wind slabs that will likely be more reactive to trigger than any existing slabs this morning, meaning: you will be more likely to trigger an avalanche on your second ski lap if conditions change. Don’t let your guard down.
The existing, larger snowpack structure remains a low probability, high consequence concern. A human or small avalanche triggering deeper into the snowpack would result in a much larger, more dangerous avalanche.
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.
The summit of Mt Washington recorded 2.6” of new snow over the last three days, and up to 2” is possible this afternoon. 2.6” doesn’t sound like much, but the thickness of a wind slab is a multiple of the snow total. Depending on the snow density, and wind speed, wind slabs can be more than 5 times the total snow depth. With our current snowpack and recent weather, new wind slabs could be 13” or more. If we receive an additional 2” this afternoon, add another 12” to the 13” for slabs over 2’ thick. We haven’t had enough recent observations or field time in the usual hotspots for this avalanche problem to be confident on how large these new wind slabs will be so make careful assessments of what you see and feel around you, and please send us an observation on what you find.
The existing upside down snow structure after the January 13 melt freeze crust keeping us at Moderate for several days is becoming less of a concern as passing time and observations continue to suggest stability.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch with good skiing most of the way down.
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 02/04/2020 at 7:11 AM.
USDA Forest Service
White Mountain National Forest
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