Avalanche Advisory for Saturday, March 14th, 2015

This advisory expires at Midnight.

Tuckerman Ravine will have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely.  Dangerous avalanches conditions exist.  Careful snowpack evaluation and conservative decision making is essential. The only exception to this is the Little Headwall which has Low avalanche danger.  Natural and human triggered avalanches are unlikely.

Huntington Ravine will have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully and identify features of concern.

These danger ratings depend on a number of weather factors today.  Read on!

AVALANCHE PROBLEM: The danger ratings and the avalanche problems are directly related to the timing of precipiation and what type.  We are starting the day with Wind Slabs being the primary concern.  The precipation shield moving from the south is a bit delayed, but the potential for rain, up to 0.15″ exists.  If light snow does transition to rain in avalanche start zones you can expect Wet Slabs  to become the main problem. Based on the density of current surface snow I believe “Wet Loose” potential is not so likely, but should be kept in mind.

WEATHER: A WINTER STORM WARNING is issued for the region. The initial pulse of precipitation is expected to begin as snow and could transition into rain within avalanche terrain. The 4000ft (1220m) elevation, and below, is currently the rough height where the rain/frozen line may be. At higher elevations we expect all snow, accumulating to 1-3″ (2.5-7.5cm). Late tonight any rain, freezing rain and sleet will transition back to snow bringing another 3-5″ (7.5-12.5cm), followed by 1-3″ (2.5-7.5cm) tomorrow. Winds will shift from the NW towards the S today and fall to 15-30mph (24-32kph). Overnight they will shift to the N, and then as the low pressure moves out, back to the NW tomorrow.  As this final shift happens winds will increase to hurricane force both increasing avalanche danger and dramatically reducing visibility on Sunday.

SNOWPACK:   On Friday afternoon we got into the field to assess conditions and found them as suspected in the advisory released in the morning.  Slab hardness from Pencil minus to 1 finger was found over the crust developed during the sunny warm up earlier in the week.  Snow, beneath a crust of varying thickness, went quickly to faceting from very cold air after the warm up.  Facet size ranged from 0.5 to 1.25mm depending on an assortment of factors.  Generally speaking where we spent time in Right gully and a beneath the buttress heading towards the Sluice there weren’t a lot of concerns with stability.  The issue that jumped out was intense spatial variability.  This had me wondering if there were more issues in larger areas of slab in the Sluice and the Lip.  These two areas hold our greatest concern this morning for human triggered avalanches and then potential Wet Slabs this afternoon. All areas have been moved up a danger rating from yesterday to account for rain potential.  Rain and cold snow over weaknesses don’t go well together.  If rain soaks into existing slabs, particularly thinner ones over facets, natural wet slabs are a potential.  If we don’t get rain and only sleet and snow you can expect 1-3″ (2.5cm-7.5cm) of accumulation to lightly load into E and NE facing aspects, but will struggle to reach today’s posted ratings.  If only snow falls a number of forecast areas will fall short of their posted “Moderate” and “Considerable” ratings, particularly slopes that face the S.  Examples include Right Gully and the Lobster Claw in Tuckerman as well as North, Damnation, and Yale in Huntington.  I think in the end we have a greater chance to get all snow in upper avalanche terrain than we do rain, but it was too great a potential to ignore.  

Snow overnight with a shifting wind will increase the avalanche danger late tonight through the early morning hours of Sunday.  Expect many areas to be at Considerable, perhaps more, for the later half of the weekend.

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 7:45 a.m. March 14, 2015. A new advisory will be issued tomorrow.

Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713