This information was published 01/19/2020 at 7:02 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Don’t commit to the steepest or largest slopes and gullies without carefully assessing the snow and terrain configuration.
Start with well supported slopes below 35 degrees without overhead hazard.
Mid slope aprons of snow which accumulated thick, hard wind slabs during the last storm could produce an avalanche more than capable of burying a person. Chute and beneath the ice cliffs in the Headwall in Tuckerman Ravine are examples.
The steepest areas previously scoured to the icy crust should be carefully assessed or perhaps best avoided altogether today since they may harbor the most reactive wind slabs. The upper ⅓ of gullies in Gulf of Slides come to mind.
Natural avalanches are possible due to continued snowfall and a west and northwest wind continuing to drift snow into east facing terrain today. CONSIDERABLE avalanche danger exists today with a complex pattern of wind slabs on an icy crust with more snow falling and wind remaining at loading speed through the day.
The most recent passing low pressure system did not produce a lot of snow but don’t ignore the upslope snow in the forecast today. Hermit Lake received 8 cm of 10% snow in the past 24 hours with the summit recording 1.6” until midnight yesterday with more snow since midnight likely doubling that figure. Higher and further north Gray Knob recorded 20cm. The new snow was accompanied by S and SW winds in the 40-60 mph range for around 6 hours that is now shifting west. Conditions are favorable for continued upslope snow with 1-3” forecast by the Obs and more forecast by the NWS. This afternoon, the summit temperature will grow cooler from the mid-teens F to 9F by dark as wind speeds abate to the 30-45 mph range.
Primary Avalanche Problem – Wind Slab
Hard wind slabs sitting on an icy crust are being loaded by more wind blown snow. These hard slabs are likely to be stubborn but can be triggered from a thin spot. New wind slabs will be more reactive with some of these slabs hiding in more northerly aspects due to a period of south wind. The potential to step down into wind slabs formed Thursday and Friday exists largely on E and SE facing wind sheltered terrain.
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.
As is often the case here in the Presidential Range, the wind slab “problem” is generally where the best skiing exists. Steep powder runs that escape wind action are rare here outside of glades and exceptional weather conditions. The distribution of wind slabs though the terrain today will be difficult to assess due to flat light and continued blowing snow. An intimate knowledge of local terrain and a strong and careful team will be key today if you venture into avalanche terrain near treeline. Ice climbs will funnel new snow into fresh and possibly reactive wind slabs in Huntington Ravine where slab avoidance should be the name of the game. Lower elevation climbs in Crawford Notch remain peppered with anchors though larger slopes and rock slabs at those elevations are worth respecting.
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 01/19/2020 at 7:02 AM.
USDA Forest Service
White Mountain National Forest
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