Avalanche Forecast for Wednesday, January 16, 2019
This information was published 01/16/2019 at 7:00 AM.
The Bottom Line
The bullseye data for any new avalanche concerns today will be the amount and rate at which new snow falls today. Though only a small amount of snow is forecast to fall, the new snow will be blown and drifted by westerly winds blowing at a perfect speed for building wind slabs. Wind slabs built on the 10th and 11th have proven unreactive in the past several days and earn a LOW danger rating today. Savvy skiers and climbers will continue to use normal precautions, especially when seeking out larger, smoother slopes for riding. Heavier snow squalls this afternoon are possible so be on the lookout for new wind slabs to form quickly if strong wind speeds combine with the new snow blowing into steep terrain generally facing east. The danger rating could rise to MODERATE quickly with small pockets of touchy wind slab forming and then growing to something more sizable.
Dry conditions continued through yesterday with moderate wind, fog and seasonably cold temperatures. A cold front will charge through the region this afternoon which presents a wild card in today’s forecast. While estimates from the MWObs and the NWS are calling for a trace to 2”, there is also the possibility of forcing that brings heavier squalls along with some thunder. This type of system often brings graupel or rimed particles which can make slabs especially touchy. Winds tonight will increase to near 100 mph as temperatures drop rapidly to around -15F. Cold but less windy conditions will follow until another round of light snow arrives Thursday night.
Primary Avalanche Problem – Wind Slab
Wind slabs formed on the 10th and 11th remain a concern, primarily due to the icy bed surface that they are resting on. New wind slabs may form today due to new snow and increasing winds from the west. The new snow falling today will build small but touchy wind slabs. These will be relatively harmless in most places until snowfall accumulates or exceeds the forecast. Both avalanche concerns will be hard to see in the terrain due to summit fog.
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.
Cold and clear conditions since the last avalanche cycle have not promoted the kind of settlement and bonding that make the older wind slab concerns go away. You may even be able to find some early facets forming near the Dec 22 ice crust that was the bed surface for the cycle of large avalanches on January 9-10. This is the kind of avalanche problem that can punish the unwary or the overconfident. Don’t be either, carry avalanche rescue gear and spread out when moving through consequential areas.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 01/16/2019 at 7:00 AM.
USDA Forest Service
White Mountain National Forest