Avalanche Advisory for Friday December 20th, 2013

Expires at Midnight Friday 12-20-2013

Tuckerman Ravine has Considerable, Moderate and Low avalanche danger. The Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Sluice and Left Gully have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.  All other areas have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

Huntington Ravine has Considerable, Moderate and Low avalanche danger. Central and Odell gullies have Considerable avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely. Pinnacle and South gullies have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.  All other areas have Low avalanche danger.  Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM:  Wind Slab in easterly and southeasterly start zones was created during the last 48 hours and will continue to grow with today’s forecasted snow. As temperatures continue to climb, this wind slab may become unstable pushing us solidly into our forecasted danger ratings for the day. Warm temperatures and potentially even some rain on the snow pack will weaken bonds especially where the Wind Slab is thinnest. Thin spots in a slab tend to be trigger points for adjacent thicker, stronger slabs which currently have grown largest on benches and discontinuous slopes in the Lip and Center Bowl area of Tuckerman and in Huntington’s Central and Odell Gully.  Be wary of any larger snowfield if precipitation rates increase or the warming trend occurs during the forecast period ending at midnight.

WEATHER: A very complex set of systems will be moving through the region over the next 72 hours having the potential to play out in a number of ways depending on the exact track and temperatures.  Today, light precipitation is expected to start as snow and potentially change to mixed conditions, hedging towards a possibility of brief rain in the afternoon.  Water equivalents (QPF) is looking to stay within 0.1” (2.5mm).  This could produce an inch of snow before moving to mixed and liquid precipitation at the 5000ft level.  Winds are expected to be from the W at 35-50mph (56-80kph) and then climbing to 50-70 mph (80-112kph) with higher gusts.  Over the weekend a storm will bring significant freezing rain (ZR) to the region and perhaps deep snow to areas north of the Presidentials.  QPF is expected between 1.2” and 1.75” (3-4.5cm) of water for Saturday through Monday morning.  The NWS has issued a WINTER STORM WATCH for 48 hours beginning Saturday at 7am.  More on this in the Weekend Update late this afternoon.

SNOWPACK: As referred to yesterday we have been getting many shots of low precipitation amounts recently.  Coupled with high winds, this has given us a substantial amount of spatial variability around both ravines.  Expect to find very different snowpack stratigraphy as you move around with different stability test results.  Today we are starting with forecast areas at the low end of their ratings.  This will climb through the spectrum of their forecast towards the upper end if we do receive a bit of rain late in the day.  As an example “the Lip” will begin at the very low end of Considerable and climb ending solidly in the middle or upper end of Considerable as we transition to liquid precipitation.  Extrapolate this concept for all forecasted ratings and locations.  In areas posted at Low small bed surfaces exist.  Stay attentive to how pockets, albeit small in size, may react to light rain.  If we do receive any more than a brief shot of scant rainfall amounts expect these locations to bump up a rating.  This is not expected to occur, but important to remember.  Expect and elevated avalanche danger through the weekend due to the incoming storm.

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 0810a.m. Friday, December 20th, 2013 . A new advisory will be issued tomorrow.

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

2013-12-20 Print