Avalanche Advisory for Friday, April 7, 2017

This advisory expires at Midnight.

Tuckerman Ravine has MODERATE and LOW avalanche danger today. Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Evaluate snow and terrain carefully. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely except on isolated terrain features. The waterfall in the Little Headwall has blown out again with open water in the stream channel.

Huntington Ravine has MODERATE and LOW avalanche danger today. Central Gully has Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely.

AVALANCHE PROBLEM: The snowpack at forecast area elevations will gain strength today as cooler temperatures allow it to freeze. Around ¾” of rain saturated most our snowpack last night resulting in widespread large rollerballs and loose wet avalanche activity. Until the refreeze takes hold of surface snow today, the possibility of small human-triggered, loose wet avalanches will remain. Moderate rated areas have a greater chance of releasing a larger wet slab avalanche from a skier or rider, or their sluff. These wet avalanche problems will be replaced by more wintry problems later. Lingering moisture will begin to fall as snow, creating the possibility of scattered areas of wind slab forming in lee areas of the southwest wind. Due to the low rate of snowfall combined with limited available snow on the ground, these wind slabs should be limited in size and distribution through the terrain until later this afternoon and tonight when wind shifts to the northwest. Anticipate wind slab avalanche danger to increase around dark and into the night as 2-4 inches more snow falls on a wind speed and direction capable of loading lee forecast areas.

WEATHER: Rainfall yesterday didn’t quite reach the full inch forecasted, but the summit still recorded 0.7” of rain. Cold is slowly returning to the mountain. Yesterday’s summit high of 36F has given way to the current 25F, which is the low temperature of the past 24 hours. Temperatures will remain steady through the day and fall slightly after dark to the high teens. Steady but light precipitation today should fall as snow in our forecast areas, with a forecast total of around 2”. Wind will be light in the ravines today, keeping the possibility for this new and fairly dense snowfall to form wind slabs to a minimum.

SNOWPACK: The recent warming and rainfall are abating, and our snowpack will undergo a slow refreeze by tonight. The existing wet slab and loose wet avalanche problems will diminish with a refreeze, however travel conditions will not improve immediately. Wet, heavy snow will begin to have a crust on the surface, making challenging ski conditions and allowing those without flotation to posthole in any snow that has not seen heavy traffic. The moisture present is minimizing our recent weak layers of concern, bringing us closer to a uniform spring snowpack which will continue to gain strength until our next warming event. Snow of up to 2” falling steadily through today on the light winds forecast will pose minimal threat of new unstable slabs until late in the forecast period. However, if snow and wind exceed forecast numbers wind slab would become a significant concern earlier than expected. Non-avalanche hazards are of equal or greater concern today: Undermined snow over flowing water increases risk of breaking a snow bridge, the imminent refreeze will likely cause ice dams to form on ice climbing routes, and this wet heavy snow is a classic contributor to knee and lower leg injuries for falling skiers. Like yesterday, the Sherburne is likely the most enjoyable ski option.

Please Remember:
• 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 caretaker at Hermit Lake Shelters.

Posted  8:15 a.m., Friday, April 7, 2017. A new advisory will be issued tomorrow.

Frank Carus/Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2017-04-07