Avalanche Advisory for Thursday, March 15, 2018

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Yale, Central, Pinnacle, Odell, South and Escape Hatch have Considerable avalanche danger. Dangerous avalanche conditions exist. North and Damnation Gullies have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. 

Tuckerman Ravine has CONSIDERABLE avalanche danger. All forecast areas have Considerable avalanche danger. Dangerous avalanche conditions exist. Lower Snowfields is still lacking snow cover though Moderate danger exists due to the Duchess runout. The Little Headwall has Low avalanche danger with pockets of unstable snow, ice and holes in the snowpack.

AVALANCHE PROBLEM: An increase in wind speed and a shift in wind direction will keep avalanche danger elevated today. Recent snowfall will be carried by NW winds and build wind slabs in many areas. Natural wind slab avalanches are possible in bigger terrain such as the Lip, Center Bowl, Chute and Hillman’s Highway in Tuckerman Ravine and Central Gully in Huntington. Dry loose avalanches are likely in the steepest areas of both Ravines and will contribute to the likelihood of human triggered avalanches on the approach to steep pitches of ice or rock. Wind slabs should become firm and stubborn with anticipated wind speeds but not before becoming unstable as they build. Staying on low angle terrain, avoiding runouts and traveling one at a time while making careful snowpack assessments will be critical today if you choose to venture into avalanche terrain. Precious little of this low angle terrain exists in our forecast zones, so seeking out lower elevation, less wind effected terrain may be your best bet until wind subsides and visibility improves.  

WEATHER: Light to moderate upslope snow showers are continuing this morning and may bring 2-4” more snow today. Almost 2” of snow water equivalent fell in the past 2 days bringing 20” of snow to the summit. Snowfall reports from the area were highly variable with this storm due to banding and intense squalls. This brings some uncertainty to our assumptions about how much snow is available for wind transport in the alpine. Though no snowfall totals are available from the west side, it is pretty clear that there is enough snow on the ground to create avalanche problems. Anticipate WNW wind to continue where it sits in the low 60 mph range and blow in the 50-70 mph range with gusts to 90 mph. Fog and blowing snow will reduce visibility and contrast and challenge visibility. 

SNOWPACK: An old adage which holds a lot of truth says that avalanche danger in a maritime snowpack is quick to rise and quick to fall. Warm temps and lots of snow normally lead to rapid settlement and bonding of grains in that snow climate. While our region and certainly the weather pattern that we’ve had lately are generally maritime, the major player in our forecast areas that defies that conventional wisdom is the action of the wind. You likely saw speedy settlement of the copious amounts of snow at lower elevations yesterday and likely much of the 8% density snow that fell at 3800’ yesterday settled some as well. But count on the polar part of our polar maritime snowpack to kick into gear with colder temperatures slowing settlement and high winds building thick and stubborn wind slabs. Recent human-triggered avalanche activity here as well as in Vermont is a reminder that our snow and weather is dynamic in our limited avalanche terrain. Don’t let the overall scarcity of new snow this winter blind you to red flags such as rapid snowfall or wind loading that signal danger. There is good skiing and riding to be had on the John Sherburne Ski Trail.

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 or Harvard Cabin.
• Posted 8:05 a.m., Thursday, March 15, 2018. A new advisory will be issued tomorrow.

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