Avalanche Advisory for Thursday, April 12, 2018

Huntington Ravine MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, South and Escape Hatch have 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. Sluice, Lip, Center Bowl, Chute, Left and Hillman’s Highway 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: Wind slabs remain the primary avalanche problem today. Small to medium sized wind slabs will become more of a threat later in the day as southwest wind increases and loads slopes further. Wind sheltered locations, especially Left and Chute in Tuckerman Ravine, yielded good powder skiing yesterday and also escaped the wrath of the hot April sun. These same aspects may receive more wind loading later today and become increasingly susceptible to triggering. If you are out in the afternoon, be on the lookout for increasing SW wind blowing and cross-loading snow from the alpine into start zones above. Wet loose avalanches may also become a problem, first as sun heats south facing slopes and later as slopes receive some rain or mixed precipitation. These smaller point release type avalanches can have remarkable pushing power as they entrain snow. Monitor your choice of slope for increasingly moist and dense snow and consider the consequences of a slide. Either avalanche type would occur over a bed surface which is icy and hard enough to be a challenge to arrest a fall on.

WEATHER: A trace of new snow fell in the past 24 hours with over 7” more in the past 48 hours. A west wind in the high 30 mph range blew again last night. Sunshine and warm conditions this morning will yield to cloud cover as low pressure moves towards the area. Temperatures in our forecast area should reach above freezing by mid-day. Warming temperatures will likely result in a mix of wet snow and rain in our forecast area with wind increasing from the 20 mph range at noon to the 40-60 mph range by sundown. The wind will shift from west to south and probably access some of the soft, recent snow remaining in our fetch in the process. A wide range of weather conditions will bring a wide range of changes to the snowpack through the day.

SNOWPACK: Avalanche activity Tuesday night and variable spring weather created a wide range of snow conditions consisting of older, stubborn wind slabs and a hard, icy crust hiding beneath the recent new snow, along with a thin sun crust on sunny aspects. There are areas of 2’ thick wind slab, especially in Central, the Lip and Center Bowl and other spots near the rollover where the old refrozen crust is lurking just beneath the new snow. While there were no signs of propagating cracks in these slabs yesterday, warming conditions could change that.  Our slopes are not at all the stable corn snow conditions that you might expect for mid-April. Continue to reduce your exposure in avalanche paths, carry avalanche rescue gear and manage your risk of long sliding falls carefully.

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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  7:55 a.m., Thursday, April 12, 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

2018-04-12