Avalanche Forecast for Tuesday, January 8, 2019
This information was published 01/08/2019 at 7:07 AM.
The Bottom Line
New snow may form small wind slabs today, however the small to large wind slabs formed Sunday night remain the main concern today. Respect these areas of drifted snow that can be identified by their smooth and pillowy appearance. These relatively hard wind slabs are notoriously tricky to assess, so don’t let your guard down. Avalanche danger is MODERATE today for a majority of our forecast areas, with the Northern Gullies of Huntington Ravine and low elevations having LOW avalanche danger due to a lack of recently deposited snow.
After mostly clear skies and diminishing wind yesterday, snow has begun to fall this morning. Just under an inch of snow has accumulated at Hermit Lake. Overnight winds reached 50 mph out of the S and have shifted SW. Snowfall should taper off by noon, with another inch or two accumulating. Wind should remain SW and begin to diminish late morning today, ultimately to around 20 mph by dark. Our terrain may receive up to a tenth of an inch of freezing drizzle this afternoon. Tonight, precipitation should intensify again and fall as all snow. Heaviest snowfall is expected tomorrow morning.
Primary Avalanche Problem – Wind Slab
New snow overnight and this morning may form small new wind slabs, but the larger avalanche problem remains the wind slabs formed Sunday night into yesterday morning. These slabs can specifically be found on the eastern half of the compass rose and vary from inches to possibly several feet thick. Areas of scouring and heavily wind textured sastrugi snow can be found, and we expect scouring to be prevalent on the west side of the range. The smooth and generally smooth wind slab will be stubborn to a human trigger today, though it is the dominant snow surface in select easterly terrain and remains capable of producing a large avalanche in such 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.
Several layers of wind slab formed over the past week comprise our upper snowpack. Those formed Sunday and into early Monday remain the primary concern, though are generally hard and therefore stubborn to a human trigger. The extreme wind speeds early yesterday also resulted in scoured areas and heavily textured snow. Visually locating the smooth wind slabs which are the avalanche problem remains a key field observation. It may be possible to avoid the avalanche problem given good visual observations. With more snow on the way, be aware that while stubborn to a human trigger these slabs may contribute to the overall size of potential avalanches tomorrow. Further, the chance of freezing drizzle this afternoon will proceed tonight’s heavy snowfall and may result in an icy crust beneath new slabs tomorrow.
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 01/08/2019 at 7:07 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest