This advisory expires at midnight.
All forecast areas of Huntington and Tuckerman Ravine have MODERATE avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features. Little Headwall and Lower Snowfield are not forecasted due to lack of snow.
AVALANCHE PROBLEM: Today’s avalanche rating and problem are based on the best information we can gather this morning. With some degree of uncertainty in the weather forecast, safe travel in avalanche terrain today will require excellent observations on the conditions at the time you are traveiling. The avalanche problem today will begin as Wind Slab and transition to Storm Slab. The avalanche danger will increase through the day as precipitation arrives, likely taking place later in the day. Wind slabs that developed over the past few days are widespread and well over a meter thick in places. These are relatively stable and can be navigated with caution and good visibility. As precipitation comes in through the day, expect storm slabs to develop in the steeper terrain. While they may be thin in places, it doesn’t take much to knock you off your feet and into a runout that still contains rocks and bushes. As the night progresses, expect avalanche danger to increase. We will likely see a good amount of something come out of the sky tonight. Whether it’s snow, ice, rain, or all three, this denser layer will sit on the lighter snow from today, creating the increased avalanche danger.
WEATHER: Yesterday was clear and calm. This lengthy period of warm temperatures allowed sintering to take place and increase the stability of the snowpack. Precipitation began early this morning as light drizzle and ice pellets. Temperatures currently in the teens will rise through the day to near freezing with S/SE winds rising to 40mph. The driving weather factor today will be the different levels of air temperature in the atmosphere. A layer of cooler air is moving in under a layer of warm air, creating mixed precipitation that will struggle to define itself through the day. Expect to see light precipitation through the day until the evening when the bulk of the low pressure arrives bringing steadier precipitation. It looks as if during daylight hours, a QPF of 0.1” will start as ice and transition to snow showers, bringing 2-4” of snow to the mountain. The heaviest precipitation looks to be during the night, with a QPF of close to 0.5”. This could result in another 3-5” of snow and sleet mixed with ice and possibly rain at times. Winds will shift to the west and may reach 55mph during the night.
SNOWPACK: Field time and observations yesterday allowed us to see our current snowpack as right-side up. Snow that arrived over the past weekend on SW through WNW winds blew into our forecast areas and built up deep wind slabs in lee areas. These are in the 1F hardness range and sit on top of the harder (P hardness) slab created by strong winds post-Nor’easter last week. Stability tests yesterday in the field produced high scores in compression tests and no propagation potential in a PST. It appears the interface between the base layer of last week’s melt/freeze crust and the Nor’easter layer is well-bonded with no signs of faceting taking place. Again, all this being said, we must now add whatever comes today on top of this. The current snowpack seems likely to accept the incoming weather with little change. Instability that develops today will likely be in the new snow. If we see the upper end of forecasted snow totals today, there is a possibility an avalanche could create the force required to impact a weak interface further down in the snowpack.
The Lion Head Winter Route is open and the most direct route to the summit from the east side of the mountain. Please be on the lookout for machine traffic on the Sherburne as we remove construction debris over the coming week.
- Safe travel in avalanche terrain requires training and experience. This advisory 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.
- Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
- For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
- Posted 8:15a.m., Tuesday, January 3, 2017. A new advisory will be issued tomorrow.
Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713