Avalanche Advisory for Thursday, February 25, 2016

This advisory expires tonight at 12:00 midnight.

All forecast areas of Tuckerman and Huntington Ravine have Considerable avalanche danger. Dangerous avalanche conditions exist. Natural avalanches are possible and human-triggered avalanches are likely. The Lobster Claw, Lower Snowfields, and Little Headwall are not posted due to an overall lack of snow in these areas.

 AVALANCHE PROBLEM: Two inches (5cm) of rain over the past 36 hours, with 3/4″ (1.9cm) or more of that falling overnight, has stressed our snowpack. Deeper layers could fail and slide in a Wet Slab avalanche as this water continues to drain through upper layers and reach weak layers below. Ice dams in the more sizable drainage channels such as the Lip waterfall in the Headwall of Tuckerman Ravine have a history of stopping up and blowing out in sizable wet avalanches. If today’s weather forecast isn’t enough to keep you away from slopes and gullies in the Ravines then the threat of a natural wet avalanche should have you choosing your route through the rotten snowpack very cautiously.

WEATHER: The bulk of the rain has passed but expect fog, rain showers and even the threat of a passing thunderstorm to continue through the afternoon. 2″ (5cm) of rain was collected at Hermit Lake in the past 24 hours. Currently summit temperature is 37F. Temperatures will begin to drop later today as a cold front passes through the area with an increase in wind speeds this afternoon. Air temperatures are not expected to reach the freezing point on the summit until sundown which will begin to refreeze our snowpack and reduce the threat of wet avalanche activity through the night. Snow showers should develop overnight with 1-3″ new snow possible.

SNOWPACK:  By tomorrow we will have officially gone through another “hitting of the reset button”.   Before yesterday’s warm up there was a high degree of snowpack spatial variability with a variety of weaknesses in different areas.  This left us a little spooked in isolated pockets and very confident on old icy surfaces.  Beginning yesterday morning light rain began across the mountain with intensity picking up late in the day.  Following a brief period of wet snow early, avalanche terrain got hit with about 1.75” (4.5cm) of rain as of 6am this morning.  Avalanche danger increased quickly through the afternoon yesterday, peaking during the overnight.  Early this morning we have come off a period of High avalanche danger and currently sit at Considerable due to concern of wet slab failure.  Through daylight hours today, we expect a slow decrease in the avalanche danger as rain and melt water continue to drain from our thin snowpack.   We are likely to pick up a bit more rain this afternoon followed by a changeover to snow.  Rain adds weight, lubricates ice lenses that restrict percolation, and melts bonds between snowpack grains reducing strength. These big three results of rain on an initially cold snowpack screams “watch out” for us.  This requires either very conservative well-thought through risk decisions using vast experience, or avoidance.  Eventually, on Friday morning the snowpack lock up will bridge over deeper concerns and the new issues may be related to new upslope snow.  This new snow is expected as temperatures drop bring us back to a potential wind slab problem tomorrow.

The John Sherburne Ski Trail today is wet with running water, is large sections of ice, however it is vastly better that the grim survival skiing you will likely encounter 24 hours from now.

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 the Harvard Cabin.
  • Posted 8:15am, February 25, 2016. A new advisory will be issued tomorrow.

Frank Carus/Chris Joosen, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856