Avalanche Advisory for Wednesday, April 11, 2018

Huntington Ravine MODERATE and LOW avalanche danger. Central Gully has Moderate avalanche danger. Evaluate snow and terrain carefully. All other forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Lip, Center Bowl and Chute have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. All other forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Six to seven inches of very low density new snow fell yesterday on light winds. Overnight, west wind reached 37 mph with small, natural avalanches resulting. Wind slabs will be the primary avalanche concern today, with medium sized avalanches in moderate rated areas causing the most concern. If winds remain as light as forecast, our avalanche problem will be limited to small human-triggered, dry loose avalanches and small to medium sized wind slabs. Avalanche activity early this morning points to the fact that the new snow remains unstable and poorly bonded to older, firm wind slabs and ice crust. While likely to be small, avalanches today may occur on a bed surface which is icy and hard enough to be a challenge to arrest a fall on. Recent avalanche activity and variable spring weather is creating a wide range of snow conditions with older, stubborn wind slabs and a hard, icy crust hiding beneath the low density new snow. Our slopes are not at all the stable corn snow conditions that you might expect for mid-April so continue to reduce your exposure in avalanche paths, carry avalanche rescue gear and manage your risk of long sliding falls carefully. 

WEATHER: Today is starting out with blue skies and calm wind and 10F on the summit. Eleven centimeters (4.3”) of 6.1% density snow fell at Hermit Lake yesterday with 7” recorded on the summit. Summit wind speed is currently blowing at 9 mph and peaked at 37 mph from the west in the early hours of this morning which likely caused the avalanches observed in Duchess and Sluice. Wind is expected to remain light and shift southwest and blow 5-20 mph on the summit. Expect sunshine to continue this morning before clouds thicken this afternoon. More new snow is expected overnight before warmer temperatures and mixed precipitation arrives in our forecast area tomorrow.

SNOWPACK: Yesterday’s new snow fell on the previous layers of wind slab formed since Friday and in some areas, the hard-refrozen crust.  This weekend’s wind events left us with 2-3 layers of wind slab of varying softness (4F-F).  The wind slab is quite spatially variable and will make snowpack observations challenging.  We expect there to be areas of 20” wind slab and spots where the old refrozen crust is lurking just beneath the new snow.   The old refrozen crust is no longer visible in our terrain but make no mistake, it still exists.  The bonding of this new snow to the varying surfaces it fell on will differ across the snowpack.  We are still experiencing a mid-winter snowpack and are by no means in a melt freeze cycle yet.

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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  8:30 a.m., Wednesday, April 11, 2018. A new advisory will be issued tomorrow.

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