This advisory expires tonight at 12:00 midnight.
Tuckerman and Huntington Ravine have MODERATE avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible in all forecast areas. Evaluate weather, snow and terrain carefully to identify features of concern. Heightened avalanche conditions will develop on specific terrain features later today.
Mixed precipitation is expected to get started in the afternoon which will push us higher into the above ratings this afternoon. The ratings above most accurately reflect the daytime recreational period. Anticipate avalanche danger to increase, moving towards Considerable near sundown and more certainly in that rating after dark.
AVALANCHE PROBLEM: Existing stability is generally good to very good in most of the forecast area either because the upper snowpack is wind packed or wind scoured, or because it was exposed to strong solar heating yesterday. Some strong lee areas, like the Chute and the left side of Center Bowl as well as other lee pockets, harbor softer slabs. These softer slabs create the potential for Wet Slab avalanches later today as mixed precipitation falls. Wind Slabs may also develop later in the day. The degree to which these wind slabs will be problematic depends upon the type and timing of the precipitation’s changeover to snow.
WEATHER: The 1/3” of new snow yesterday evening did little to impact our stability. More precipitation is forecast for the afternoon with 1/4″ of water equivalent by dark and another 1/2″ or so through the night. The good news is that it will be getting colder with mixed precipitation on the summits turning to increasingly lighter snow overnight. The bad news is there is some chance for rain, in addition to freezing rain, sleet and snow, in our avalanche forecast area for a period this afternoon. Though not a tremendous amount of precipitation, it may be enough to weaken some existing softer surface slabs or penetrate thinner slabs. The type of precipitation is a wild card due to the position of the melt/freeze line within our forecast area. Keep a close eye on temperature and incoming precipitation since they will directly impact stability today. As mentioned above, snow this afternoon and evening will increase and grow less dense as the cold front arrives with 2-4” expected to fall on diminishing winds overnight. Favorable conditions for upslope generated snow showers are forecast tomorrow with west winds potentially in the light range. Expect a new wind slab problem tomorrow and a return to wintry weather.
SNOWPACK: Generally firm or hard snow predominates in our terrain due the freeze/thaw cycle that started on Tuesday. Though summit temperatures that day never climbed to the mid-teens, the strong sunshine and dead calm wind in the forecast area allowed significant warming, even in shaded areas. Yesterday, it was apparent that south facing ice climbs in Huntington took a beating and slopes in Tuckerman developed peel away corn snow. Cooler temperatures overnight have no doubt hardened these aspects but the damage to ice features remains. Expect a hard surface requiring crampons and an ice axe in most areas today. As a reminder, the warm temperatures over the past two days have not created a stable, isothermal spring snowpack. Be wary of weak layers buried well down in the snowpack particularly in slightly lower elevation, lower angled terrain outside our forecast area. Deeper weak layers in our terrain also exist but will most likely require more than today’s precipitation to activate.
- 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 8:26 a.m. Thursday, March 26, 2015. A new advisory will be issued tomorrow.
Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713