General Bulletin, Wednesday, December 11, 2019

This information was published 12/11/2019 at 6:33 AM.
New information will be issued when conditions warrant.


The Bottom Line

The recent warm-up and rain settled our snowpack which is now refrozen in steep terrain. Be aware of the potential for a long, sliding fall into rocks or trees if you venture out to hike or climb. It’s next to impossible to self-arrest on bulletproof, refrozen snow so choose your route carefully. Also, strong winds may quickly build small areas of unstable wind slab with surprisingly small amounts of new fallen snow due to fall this week. Look for these unstable wind slabs in steep gullies, behind and beneath steep terrain features and anywhere that is sheltered from the wind. The rain soaked and now frozen snow surface often bonds poorly to new snow. Even small avalanches can be a problem, particularly with the refrozen, icy snowpack that exists where self arrest or escape can be difficult.

2019-12-11 Printable

 

Danger Rating

General Bulletins are issued when unstable snow may exist within our forecast areas but before conditions or available resources warrant 5-scale avalanche forecasts to 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.

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.

Mountain Weather

Nearly an inch (23mm) of rain fell at Hermit Lake and Harvard Cabin through Tuesday. Light snow showers began on the summit Tuesday afternoon as winds as northwest flow returned. Expect cold temperatures around zero fahrenheit until warmer southwest flow brings mixed precipitation on Friday. Some more snow and seasonably cold temperatures return for the weekend. You can keep tabs on daily details of snow on the ground and 24 weather at our snowplots at the bottom of the forecast page of this website along with the weather resources, including a daily F6 report,produced by the Mount Washington Observatory on the summit.

Forecast Discussion

Warm temperatures and rain early in the week brought significant settlement to the snowpack. Where several inches of 5% density snow combined with more typical 10% snow existed, there is now a refrozen and stable deeper snowpack. It remains to be seen whether the rain triggered any wet snow avalanches in the terrain, though some wet loose sluffs seem likely. If you see chunky debris or sluff channels, post a photo or two on our Observations page to let us know where and when you saw it.

A cycle of natural avalanches occurred overnight last Saturday with crownlines visible in the Sluice and in the Lip area of Tuckerman Ravine. As expected with the relatively undeveloped snowpack, this activity was limited to small D1 avalanches. A period of wind loading forming slabs from the incredibly light 5% snow likely failed very readily with other skiable terrain sluffing frequently or being skier compacted Friday and Saturday. The only other really viable ski terrain so far is Huntington which has seen some traffic and no reported avalanches. 

The avalanche activity that has occurred, including the human triggered avalanche in Chute last month, is a reminder that avalanches can and do occur here. Travel with a skilled partner, don’t hang out in the runout of avalanche paths, ski one at a time and always wear and carry your avalanche rescue gear. Islands of safety are hard but not impossible to find.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
04/13/20
06:15
0 CM 0.1 MM0CM206 CM-3.5 C7.5 C-7.0 COvercastRain
04/12/20
06:20
Trace 1.8 MMTrace216 CM-7.0 C-4.0 C-7.0 CFewNo precipitation
04/11/20
06:20
14 CM 23.1 MM 14%62CM222 CM-8.0 C-6.0 C-8.0 COvercastNo precipitation
04/10/20
06:30
53 CM 49.5 MM 12%NC200 CM-6.0 C-2.0 C-6.5 COvercastSnowView
04/09/20
06:25
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 12/11/2019 at 6:33 AM.

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