This information was published 03/17/2020 at 7:12 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Drifting snow will form wind slabs today that may not eliminate the current hazard of long sliding falls. Avalanche danger will increase to MODERATE as snow accumulates and is affected by the wind. Watch for drifting snow that may form quickly on lee aspects and cross loaded terrain.
Our current hard and slick snow surface presents a significant sliding fall hazard, and a greater concern early in the day when even a small avalanche could result in a long sliding fall. Crampons, ice axe and the skills to not fall are required tools today.
Yesterday, skies remained clear until late afternoon. Wind speeds were low and temperatures barely pushed past single digits.
Today, a fast moving system will bring snow to mid and upper elevations. Snow showers this morning will become steady snow before tapering back to snow showers this afternoon. 1 to 3” of snow are possible. Lower elevations will likely see snow turn to rain midday. Wind is forecast to remain from the SW at 50-70mph for most of the snowfall, shifting to the W as the front pulls away in the afternoon, then to the NW this evening and increasing to 60-80 mph. Snow showers may continue into the night with an additional trace to 1” possible.
Tomorrow, skies are forecast to clear before clouds and snow showers return for the evening. Wind from the NW at 50-70 mph will shift W and decrease to 30-45 mph. A trace to 1” from snow showers is possible.
Primary Avalanche Problem – Wind Slab
Wind speeds capable of transport, combined with new snow will build wind slabs through the day. Look for wind drifted snow as the avalanche problem today. Wind slabs will likely be small, though reactive early in the day and may become larger if we see the upper end of the forecast totals, especially once the wind shifts west. Our terrain starts the day with an ice crust and refrozen surface. Given the slick bed surface and long sliding fall concerns, consider the consequence of even a small avalanche knocking you off your feet in your terrain choices. Snow changing to rain at lower elevations, and a general lack of snow at lower elevations will limit this avalanche problem to mid and upper elevations.
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.
Snow rangers at MWAC wear many hats. As avalanche forecasters, we remain unbiased and work with the data to create an avalanche forecast that’s accurate as best we can. As rescuers, we are crossing our fingers that this new snow builds and is widespread to eliminate the sliding fall hazard that’s at the top of our minds. Looking at weather forecasts this morning, the MW OBS is calling for 1-3” while the NWS has 4.5” forecast from almost 0.5” of water. The rescuer half of my brain thinks it’s possible that snow totals could end up closer to the NWS forecast if the front moves a little slower and while that’s not a big difference, it may be enough to help cover this ice crust and reduce the sliding fall hazard.
The Sherburne and Gulf of Slides ski trails are snow covered 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 03/17/2020 at 7:12 AM.
USDA Forest Service
White Mountain National Forest
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