This information was published 04/09/2020 at 7:18 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Snow begins this morning up high and will fall more heavily this afternoon with 3-4” or so falling by dark. Expect visibility to diminish quickly as snow falls more heavily at times. Southeast wind speeds won’t have much snow to work with today but could push the danger rating above our forecast LOW if snowfall exceeds the forecast. Avalanche danger will rise rapidly through the night as the wind shifts to the northwest with natural wind slab avalanches possible by morning in predominantly east and southeast facing terrain and likely in Tucks. A refrozen crust beneath the new snow will make for a hard, slick bed surface with sliding fall potential until it’s buried.
Yesterday, calm winds and mild temperatures allowed snow surfaces to soften but cloud cover limited this effect to sunny aspects. Summit temperature was in the mid-20’s through the day.
Today, clouds will build with snow developing in the afternoon. 3-5” is expected by midnight. Wind will be primarily from the southeast at 30-45mph until a shift to the northwest occurs later tonight. 2-4” more will fall through the night, making this 5-9” available to a 50-70 mph northwest wind by dawn.
Tomorrow, snow continues with another1-3” falling through the day with wind increasing further to 65-80 mph with 100 mph gusts.
Primary Avalanche Problem – Wind Slab
Snow begins this morning up high and will fall more heavily this afternoon with 3-4” or so falling by dark. Southeast wind speeds won’t have much snow to work with today but could push the danger rating above our forecast LOW if snowfall exceeds the forecast. Keep an eye on rate of snow fall and wind speed and direction changes.
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.
Graphical NWS models align well with MWObs snow forecast total through today and tomorrow despite the narrative description being much too high. Some uncertainty in snowfall totals seems apparent though since cooling due to snowfall rate can push the snow density up or down.
NWS avalanche watch and warning products are being considered but since they may serve to lure the public which is otherwise doing well with stay-at-home order, we are likely not to issue this product.
Rapid warming of wind slabs due to sunshine and warm temps on Saturday and Sunday will be a recipe for human triggered and possibly natural wet avalanches.
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 04/09/2020 at 7:18 AM.
USDA Forest Service
White Mountain National Forest
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