Avalanche Advisory for Saturday, April 7, 2018

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central Gully has Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. The Little Headwall is not forecast due to a lack of snow.

 AVALANCHE PROBLEM: New snow overnight on increasing W wind makes new wind slab our primary avalanche problem. A lack of visibility into the terrain adds an element of uncertainty to this advisory. We expect the new snow to have trouble sticking to the hard refrozen surface that existed prior to this storm. This indicates two key characteristics of today’s avalanche problem. First, new slabs will likely be touchy to a human trigger. Second, we expect that some areas are scoured by wind to the old refrozen surface. This scouring affect is likely occurring to the greatest degree in our upper start zones. Altogether this means that we have touchy new wind slabs that will vary in size. Largest slabs are expected in middle to lower avalanche start zones of Considerable rated areas, where you are likely to trigger an avalanche. Natural avalanches are possible in these areas, making the floor of Tuckerman Ravine an unwise place to linger. Additionally, be aware that the hard old crust either beneath new snow or at the surface will make it nearly impossible to arrest a long sliding fall.

 WEATHER: Six inches of snow was recorded in the past 24 hours at Hermit Lake, with wind that has shifted from S to W and increased to the current sustained 60 mph on the summit. This wind likely affected the recorded summit snow total which was only 3”. Snowfall has tapered to light amounts, though we could receive another trace to 3” this morning from upslope showers. It’s currently 10F on the summit and 18F at Hermit Lake. Temperatures should drop a handful of degrees through the day as mostly cloudy skies persist and wind decreases slightly while shifting NW. Tonight and tomorrow will trend toward clear skies, with minimal precipitation, moderate wind, and wintry temperatures.

SNOWPACK: Our new snow has fallen on a very hard refrozen surface that it will generally struggle to bond with. This older refrozen layer also limits any concerns for deeper instabilities. We expect new wind slab to vary from small to large and for the terrain to also have areas where wind has scoured to the old refrozen surface. A lack of visibility this morning prevents us from confirming the size and distribution of new wind slab. The same visibility challenge will apply to your observations and decisions on the mountain today. Realize that if you can’t see terrain above you, you can’t evaluate its potential to produce a natural or human triggered avalanche. Six inches of new snow can easily build to slabs of 2 feet or more with the wind speeds we’ve seen overnight. It’s wise to choose low consequence terrain on days like today, which have a high degree of uncertainty. The Sherburne Trail should ski well today, though watch out for some thinly covered rocks.

 Check our Instagram for photo updates, we’ll post more specific information if we get any visibility today! You don’t need an account, just follow the link on our website.

 Boston folks: Join us on Tuesday, April 10, from 7-10 pm at Arc’teryx Boston for a night of learning, socializing, and free gear! Free to attend, but space in limited, register at eventbrite.com.

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 caretakers at Hermit Lake Shelters.
• Posted  8:00 a.m., Saturday, April 7, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2858

2018-04-07