This information was published 03/03/2020 at 7:15 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Warming wind slabs are the concern today as temperatures rise above the seasonable norm. If the sun comes out south facing slopes may see temperatures rise well above the ambient air temperature, working to intensify this destabilizing snowpack problem. Watch for moist snow as a sign that the likelihood of a human triggered avalanche is increasing.
At lower elevations, temperatures are forecast to reach into the 40’s F creating hazards in addition to wet loose avalanches that include falling ice as frozen waterfalls crumble and detach from the rock.
Yesterday, light afternoon snow showers produced almost 1” of snow on the Mt Washington summit while the Hermit Lake snow plot received just a trace. Wind was from the west at 50-60 mph. Temperatures climbed steadily through the day, beginning in the upper teens, and ending in the upper 20’s on the summit and 33F at Hermit Lake.
Today, we start the day at 27F on the summit, and 32F at Hermit Lake. Cloudy skies may clear partially mid-day, before becoming cloudy again in the afternoon with the approaching storm system. Temperatures will climb slightly or remain steady during the day, however if skies clear enough temperatures will quickly rise to well above freezing on south aspects. A trace to 2” is possible this evening, likely beginning just after dark and continuing overnight and into tomorrow. West wind at 50-60mph will shift S and decrease to 30-45 mph.
Lower elevations will likely see precipitation fall as rain late in the day.
Tomorrow, snow showers may bring 1 to 3” of new snow, colder temperatures in the teens F, and NW wind increasing 75-95 mph.
Primary Avalanche Problem – Wind Slab
Warming today is a red flag that snowpack stability is decreasing. The possibility of a human triggering a wind slab today rises as warm temperatures work to reduce the strength of the snowpack. This will be especially true on southerly aspects if the sun comes out midday driving temperatures higher than what is forecast. Obvious signs of warming snow are rollerballs, but you can check for more subtle clues by sticking your hand in the snow and feeling for wet/moist or dry snow. Wet snow, and how deep is the clue for a destabilizing snowpack 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.
Secondary Avalanche Problem – Wet Loose
Wet loose avalanches are possible today as the warm air and sun melt the snow surface increasing the water content in the snowpack. These avalanches will likely be small in size, though have consequence in steep terrain capable of pulling you off your feet. Elevations below 3500 feet will be the area of greatest concern, and much less likely at mid elevations.
What is a Wet Loose Avalanche?
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
The terrain going into today includes a mix of chalky firm snow found mainly on southern aspects and 4F to 1F wind slab found in locations protected from the moderate winds we’ve had since the weekend snow. Yesterday, field observations showed the softer wind slabs to be generally unreactive though upside down in structure. The main topic of the morning forecasters discussion was the concern of warming, and just how warm the snow pack will get. One way a wind slab can fail is by adding stress, such as a skier or snowboarder. Today’s problem is the chance for a wind slab to destabilize due to adding moisture from the melting snow surface, which then may more easily fail by the added stress of a recreating human.
Clearly, lower elevations will see very warm temperatures and even a chance of rain which is certain to weaken the snowpack. Upper elevations will likely stay cold enough that warming won’t be an issue. Middle elevations, in the ravines, is where the uncertainty lies as it’s difficult to predict just how much an affect the elevated temperatures will have.
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 03/03/2020 at 7:15 AM.
USDA Forest Service
White Mountain National Forest
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