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.

Danger Rating

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

Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
0 CM 0.1 MM0CM206 CM-3.5 C7.5 C-7.0 COvercastRain
Trace 1.8 MMTrace216 CM-7.0 C-4.0 C-7.0 CFewNo precipitation
14 CM 23.1 MM 14%62CM222 CM-8.0 C-6.0 C-8.0 COvercastNo precipitation
53 CM 49.5 MM 12%NC200 CM-6.0 C-2.0 C-6.5 COvercastSnowView
0 CM 0.0 MM0CM158 CM-1.0 C8.0 C-4.5 CClearNo precipitation

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
05/25/2054 F46 F 0.0 in 0.0 in18.7 MPH44 MPH

260 (W)

05/24/2054 F40 F 8.3 in 21 in8.3 MPH21 MPH

280 (W)

05/23/2055 F43 F 0.0 in 0.0 in15 MPH45 MPH

300 (WNW)

05/22/2055 F40 F 0.0 in 0.0 in37.4 MPH67 MPH

290 (WNW)

05/21/2053 F38 F 0.0 in 0.0 in29.4 MPH59 MPH

280 (W)

05/20/2050 F34 F 0.0 in 0.0 in29.4 MPH59 MPH

280 (W)

05/19/2041 F27 F 0.0 in 0.0 in15.3 MPH36 MPH

100 (E)

05/19/2050 F34 F 0.0 in 0.0 in11.4 MPH25 MPH

30 (NNE)

05/18/2045 F30 F 0.0 in 0.0 in14.7 MPH36 MPH

70 (ENE)

05/17/2040 F30 F 0.0 in 0.0 in17 MPH35 MPH

270 (W)

05/16/2037 F28 F .16 in 0.0 in38.8 MPH101 MPH

310 (NW)

05/15/2042 F32 F .95 inTrace 31.5 MPH95 MPH

250 (WSW)

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