General Avalanche Advisory 12-28-2011

A new advisory will be issued when conditions warrant or within 72 hours.  Unless updated this advisory expires Friday 12-30-2011 at midnight.

This is an early season GENERAL AVALANCHE ADVISORY for Tuckerman Ravine.  We have not yet begun posting advisories for Huntington Ravine due to an overall lack of snow cover in this area. These will begin when conditions warrant.

General Advisories are issued when instabilities are isolated within the entire forecast area. However, avalanche activity may occur within these locations before the issuance of a 5-scale danger rating forecast. Under a General Advisory you need to make your own snow stability assessments when traveling in avalanche terrain. Within the General Advisory there are isolated snowfields that are growing in size and may harbor instabilities. In Tuckerman the two largest snowfields can be found in Left Gully and the Chute. Some smaller snowfields are also developing in the Center Bowl and other areas towards the north. Conditions are changing quickly, so check the latest advisory before heading into avalanche terrain.

With each waking day we get closer to full on winter.  As of 7am this morning the summit picked up 7.2″ of snow with some additional freezing mixed precip and just a hair of rain all melting to almost 2.2” (5.6cm) of water during the previous 24 hours.  Meanwhile down at the Hermit Lake elevation 2” (5cm) of snow fell along with a number of other precipitation forms including rain all melting to 1.65” (4.2cm).  Down low in the Ravine at the Lunch Rocks elevation the surface consisted of a 1.5” (3.75cm) thick porous crust with moist snow underneath, but not quite to the “wet” definition.  It is likely that as you gain elevation the crust will become thinner as less liquid and mixed precipitation fell the higher you move towards the summit.  This morning the temperature started dropping quickly on Washington’s high point from 32F (0C) at 3am to 14F (-10C) as of 2pm.  With this drop in temperature and the frontal movement upslope snow began falling and is expected to continue overnight.  The main concern at this point is new cold dry snow loading on a number of different crust and surface textures depending on snowfield elevation.  New snow this afternoon and tonight with be loaded into the Ravines on increasing NW winds expected to peak around 115mph and will be sustained at about 100 for a lengthy duration. Temperatures will also be the coldest yet with a mercury expectation of -15F (-26C) overnight and only rebounding to 0F (-18C) on Thursday if we’re lucky.  New upslope snow crystals will be light in density, but should get pulverized and packed into strong lee areas by high NW winds in a number of places and scoured out in slopes exposed to the 100+mph winds.  We would expect any new snow that survives the high winds scouring effects to have a poor bond at the interface with old surface crust. Also we are expecting an enormous near surface temperature gradient which will start a rapid faceting process in a number of locations depending on the thickness of new snow deposition over the crust.  So… we are getting closer to some more significant issues and will continue evaluating the situation day by day as we move closer to a 5 scale danger rating situation.  We will have some new information out for the holiday weekend as we observe changes over the next 24-48 hours.

OTHER EARLY SEASON CONCERNS— Trails going through ravines and gulfs require winter gear, equipment, and skills. Also, streams and water crossings are still in the process of freezing over, including on the trail leading into both Tuckerman and Huntington Ravines. All this can make getting to a ravine challenging, and once you get there you’ll be faced with typical early season conditions such as thin ice, water flowing behind ice, exposed loose rock, and thin snow cover in most of the usual ice climbing routes.

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 12-28-2011 3:00pm.

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

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