Avalanche Advisory for Monday, April 23, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Yale, Central, Pinnacle, Odell, and Escape Hatch have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. North, Damnation, and South have Low avalanche danger. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Right Gully, Sluice, Lip, Center Bowl, Chute, Hillman’s Highway, Lower Snowfields have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. Lobster Claw and Left Gully have Low avalanche danger. Watch for unstable snow on isolated terrain features. The Little Headwall is the exception with Low avalanche danger and areas of open water.

AVALANCHE PROBLEM: Wind slabs that formed over the weekend will still be our primary concern today. Warming yesterday may have allowed some additional bonding of these wind slabs to the icy bed surface.  While they appear similar, these slabs are variable depths across the terrain.  They proved firm and stubborn to human trigger yesterday however that doesn’t mean they are stable.  We would expect an avalanche today to be medium to large in size, particularly in Moderate rated terrain. Again today’s problem makes it a relatively low probability, high consequence day.  With the rising temperatures today spring hazards should being part of your travel decision making.  The forecast temperature and solar gain for today will help move us toward a traditional spring snowpack.  However, we have not reached this point yet so please continue to bring your avalanche gear and a mid-winter mindset.

 WEATHER: Yesterday the summit reached 20F while Hermit Lake reached 36F.  The wind stayed steady at 30 mph out of the NW with gusts reaching 50. High pressure has set up over the Northeast, with the center moving over us today.  This high will help decrease our winds to 10-25mph and shift them from NW to W.  It will also bring warmer air from the West and help us reach more seasonable April temperatures.  Today the summit should reach the mid 30 F and only drop to the upper 20’s F overnight. Tomorrow warmer temperatures continue with the high on the summit expected to reach 40F.  Cloud cover should increase late in the day with an incoming weather system.

 SNOWPACK: The up to 16” of snow and consistent loading wind speeds have created wind slab across much of our terrain. The bed surface is still the icy, hard crust formed from last week’s mixed precipitation and refreeze.  The slab varies greatly in depth from several inches to multiple feet.  The depth, along with the hardness, is hard to visually assess from the surface.  During observations yesterday we found 2’ thick layer wind slabs in close proximity to 2” of slab on top of a shallow graupel layer, illustrating current spatial variability. Bonding of the slab to the bed surface likely improved yesterday but not to the point of calling it stable.  With the warming temperatures and increasing solar gain today we expect peak instability to coincide with peak temperature. While sun should soften snow on the surface today, don’t expect an instant transition to corn snow from our late season wintry snowpack.  It is always a good idea to choose terrain appropriate to your preparedness and respect avalanche danger.

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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  8:10 a.m., Monday, April 23, 2018. A new advisory will be issued tomorrow.

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