General Bulletin for Sunday, December 15, 2019

This information was published 12/15/2019 at 7:34 AM.
A new bulletin will be issued when conditions warrant.


The Bottom Line

Winter conditions return with a vengeance on Sunday with high winds and new snow turning things around after a significant warm-up and rain event. Extreme winds will make travel anywhere above treeline challenging to say the least, with falling temperatures and blowing snow further complicating matters. Wind will increase even further Sunday night with 140 mph gusts possible. Upslope snow showers could bring 3-6 inches of new snow. High winds will pound the new snow into stiff wind slab that may remain unstable through Monday. Flowing water will build ice again but beware of ice dams and undermining until a more thorough freeze returns.

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.

2019-12-15 General Bulletin printable

Danger Rating

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 damage to trees and roots.) The Sherburne ski trail no doubt received a beating by rain and warm temperatures. Be wary of rocks and open water bars when new snow arrives.

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:

Undermined snow and ice – Two and a half inches of rain plus snowmelt brought near flood stage conditions to the alpine. Anticipate damage and undermining.

 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.

Mountain Weather

Graupel (snow pellets) is falling again at Hermit Lake Sunday morning after the recent deluge dropped 2.4” (60mm) of rain at this location. Strong west winds will howl as the temperature plummets Sunday and into Monday with steady winds in the 80-100 mph range with gusts to 140mph! High winds will diminish through the day Monday.  Low temperatures on the higher summits will reach below zero F before rising into the teens as another coastal Low pressure system approaches, bringing snow on Tuesday.

Forecast Discussion

We’ve had several avalanche cycles this season in Tuckerman Ravine with some avalanche paths filling in to the floor. While the warm-up and rain did some damage to ice climbs and the snowpack, we only lost 5cm of snow at the stake at Hermit Lake. This is an indicator that the nooks and crannies between boulders and in the krumholz are still mostly filled in with snow which will allow most new snow arriving in the next few days to be transported by any westerly wind into east aspects. Though likely to be stubborn to triggering due to extreme wind action pounding the particles tightly, look for a layer of graupel that could serve as a weak layer. Another storm arrives Tuesday and will hopefully replenish our snowpack. Close to 2.4 inches (59.6mm) of rain fell at Hermit Lake Friday and Saturday. Expect this volume of water to undermine snow and ice.

Additional Information

Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Click here to check it out.

Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit a photo or two and a brief description of snow and avalanche information that you gather in the field.

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 12/15/2019 at 7:34 AM.

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