General Bulletin for Thursday, December 5, 2019

This information was published 12/05/2019 at 6:37 AM.
New information will be issued when conditions warrant.


The Bottom Line

Be on the lookout for fresh windslab particularly at the base of the steepest terrain or where wind piles it into pillows of hollow sounding slab. Most snow fields and gullies are not filled in yet so any avalanche activity should remain on the small side. The flip side of this is that the poorly developed snow fields and gullies have many obstacles and terrain traps in them. Small, early season avalanches can carry significant consequences due to the ease with which an avalanche can bury a person on a low angle bench or sweep them off a cliff.

General Bulletins are issued when unstable snow may exist within our forecast areas but before 5-scale avalanche forecasts begin. We will start 5-scale forecasts on Wednesday, January 15 or earlier, if possible. Please remember that avalanches can and do occur before 5-scale avalanche forecasts are issued.

North American Danger Scale

The recent weather system that passed well to our south dropped around 5” of new snow. This new snow was blown into largely stubborn wind slabs or scoured to older, edgeable old snow. New snow in the form of upslope showers is in the forecast as we move into the weekend.

The Tuckerman Ravine and Huntington Ravine trails are challenging climbs with significant avalanche hazard during winter. Both have been the scene of serious accidents where they pass through the steepest terrain of these Ravines. The summer Lion Head Trail remains the safer choice for accessing the summit of Mount Washington from the east. As more snow falls and avalanche paths grow on the summer Lion Head trail, the Lion Head Winter Route will become the preferred route to the summit. Using the Lion Head Winter Route too early causes significant erosion and resource damage. An ice axe and crampons are currently needed at treeline and above. The Sherburne ski trail has snow coverage to the parking lot though numerous water bars remain partly open. Most but certainly not all rocks are covered.

Ice climbs are growing in size and pockets of unstable snow between ice pitches are notorious for causing problems.  In addition to avalanche hazards, remember to take into account other early season hazards that exist in the terrain:

  • Rocks, trees and bushes lurk in the snow and in the fall line. Skiing or sliding into obstacles can ruin your day or worse. New snow may just barely cover a season ending stump or boulder.
  • Terrain traps and cliffs make burial and significant injury a real possibility, even if you are only swept off your feet by a small avalanche.

2019-12-5 General Bulletin

Mountain Weather

The weather Thursday through Friday night may bring 6” or more new snow. Wind from the west will carry snow into east facing terrain. Wind speeds will scour some areas and build wind slabs in others. Temperatures will be around 0 F with low visibility at times due to summit fog and blowing snow. Forecasts indicate warmer conditions, clearing skies and improved visibility for the weekend. 

Forecast Discussion

One of the five classic red flags often used to determine avalanche danger is recent avalanche activity. A human-triggered avalanche on Friday, November 29 is a good reminder that avalanches can and do occur on smaller snowfields. New snow and wind-loading are two more of these red flags. As always, make careful assessments of snow and terrain on an ongoing basis. Waiting 24 hours after loading or new snow has stopped is a rule of thumb that allows new wind slab or new snow instabilities to heal and bond, with more time needed during colder weather or with a very smooth bed surface. 

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
01/19/20
05:15
8 CM 7.3 MM 10%NC112 CM-6.5 C-6.5 C-15.0 COvercastSnow
01/18/20
05:15
0 CMTrace 0CM103 CM-18.5 C-12.0 C-22.0 COvercastNo precipitationView
01/17/20
05:11
22 CM 16.6 MM 9%26CM107 CM-20.0 C-4.0 C-22.0 CFewNo precipitation
01/16/20
05:15
3 CM 2.9 MM 11%NC85 CM-7.0 C-4.0 C-7.0 COvercastSnow
01/15/20
05:16
2 CM MM 16%NC82 CM-4.0 C-3.5 C-7.0 COvercastSnowView

Avalanche Log and Summit Weather

Thank you Mount Washington Observatory for providing daily weather data from the summit of Mount Washington.

DateMax TempMin TempTotal (SWE)24H Snow & IceWind AvgWind Fastest MileFastest Mile DirAvalanche Activity
01/17/204 F-18 F .03 in .4 in75 MPH110 MPH

320 (NW)

01/16/2018 F-11 F .048 in 6.1 in43.3 MPH117 MPH

330 (NNW)

01/15/2020 F11 F 0.25 in 1.8 in9.3 MPH74 MPH

290 (WNW)

01/14/2020 F10 F 0.03 in 0.7 in32 MPH69 MPH

280 (W)

01/13/2022 F14 F .04 in .8 in49.5 MPH81 MPH

240 (WSW)

01/12/2045 F8 F .84 in .4 in58.4 MPH104 MPH

260 (W)

01/11/2042 F29 F .32 in 0 in68.8 MPH119 MPH

230 (SW)

01/10/2030 F12 F .22 in 1.3 in63.4 MPH102 MPH

260 (W)

01/09/2015 F-14 F .04 in .4 in50.1 MPH114 MPH

310 (NW)

View
View
01/08/2013 F-8 F .52 in 5.2 in43.5 MPH95 MPH

290 (WNW)

01/07/2016 F1 F .17 in 1.6 in41.8 MPH90 MPH

280 (W)

01/06/2010 F3 F .2 in 2.2 in32.8 MPH71 MPH

270 (W)

Please Remember:

Safe travel in avalanche terrain requires training and experience. This forecast 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.

Avalanche danger may change when actual weather differs from the higher summits forecast.

For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.

Posted 12/05/2019 at 6:37 AM.

Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest