Avalanche Forecast for Wednesday, December 19, 2018

This forecast was published 12/19/2018 at 7:09 AM.
A new forecast will be issued tomorrow.

The Mount Washington Avalanche Center will no longer issue daily avalanche forecasts for the 2018/19 season. Read more

The Mount Washington Avalanche Center will no longer issue daily avalanche forecasts for the 2018/19 season. Instead, we will post an updated General Bulletin as needed, in case of significant snow or weather events that might vary from the typical daily changes that come with spring weather. We will also keep you informed about the official closure of the portion of the Tuckerman Ravine Trail from Lunch Rocks through the Lip and Headwall as well as the switch from the Lion Head Winter Route to the summer trail. Observations from the field will continue to be a valuable resource, so please keep submitting photos, videos and observations here and we will do the same. Check the Forecast page for update on Sherburne Trail closures, which are imminent as spring snowmelt continues.

The switch to a General Bulletin does NOT mean that the mountains are now a safe place to ski. The hazards which emerge in the spring are significant and require careful assessment and strategic management. If you have never skied Tuckerman, peruse our Incidents and Accidents page for spring related incidents involving avalanches, long sliding falls, icefall, crevasse and moat falls, and other incidents related to diurnal changes in the snowpack. These will help you understand and plan for these hazards.


The Bottom Line

Strong winds in the past 24 hours pounded the 4” of snow that fell in the past 48 hours into our steep slopes. The resulting wind slabs are likely to be very stubborn where you find them in the most sheltered terrain. Unfortunately, they may be resting on a slippery ice crust or a combination of ice crust with a weak faceted layer nearby. Steep slopes with an aspect facing away from the hurricane force northwest winds may contain larger but stubborn wind slabs. Consider these slopes to have  MODERATE avalanche danger today. It may be possible for a rider or climber to trigger one of these slabs. Wind erosion has likely scoured many other slopes and gullies. These areas will have LOW avalanche danger due to smaller wind slabs.

2018-12-19 Printable PDF

Danger Rating by Zone

Mountain Weather

Howling NW winds died down overnight. Yesterday’s highest gust reached 117 mph with almost 12 hours of wind in the high 80 to 100 mph range. 1.6” of new snow was recorded on the summit in the past 24 hours. Our well sheltered snow plots saw significant wind scouring and drifting in the past 24 hours. Temperature will rebound today and has already risen to 9F following a low temperature yesterday of -9F. Expect NW winds to continue to diminish to a much more hospitable 50 mph. The high temperature will reach into the low 20’sF on the summit under clearing skies.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Steep leeward slopes which did not avalanche yesterday will be stubborn to the point of being unreactive today. Despite their steely and stiff nature, it’s best to continue to use normal, safe travel precautions when travelling on or below these slabs.

What is a Windslab Avalanche?

  Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Snowpack and Avalanche Discussion

It remains to be seen what natural avalanche activity occurred yesterday due to the lack of visibility. Four inches of snow in the past 48 hours, plus whatever snow the howling winds dug up and moved, likely generated a decent avalanche cycle on eastern aspects and may have even ripped up some of the rain crust scattered around the terrain, both in the alpine and in the ravines. If you are digging or doing stability tests, you’ll likely find fractures initiating at moderate load force but not likely to see much snow with propagation potential. The ability of slabs to propagate a crack is a better indication of slope stability in wind slabs than the tendency of the weaker interface to crack, which it almost always does.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. Following yesterday’s wind event, you’ll want sharp edges on your skis and quick reflexes for dodging limbs on the ground.

Avalanche Safety Information Study

Please contribute to the effort to improve backcountry avalanche forecasts! Researchers in Canada devised a study to better understand how we communicate the avalanche risk, and we need your help. Please fill out this survey. It will take a few minutes, but it will help us as we work on new ways to give you the most important avalanche information.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
05/20/19
05:30
0 CM 20.4 MM0CM68 CM11.0 C12.0 C3.5 CObscuredNo precipitation
05/19/19
05:25
0 CM 0.0 MM0CM72 CM4.0 C6.0 C2.0 COvercastNo precipitation
05/18/19
05:20
0 CM 7.6 MM0CM80 CM1.0 C6.0 C1.0 COvercastNo precipitation
05/17/19
05:25
0 CM 0.8 MM0CM84 CM4.0 C10.0 C0.0 CClearNo precipitation
05/16/19
05:20
0 CM 0.0 MM0CM84 CM1.0 C1.5 C0.0 CFewNo precipitation

Avalanche Log and Summit Weather

Daily Observations


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
05/19/1951 F34 F .6 in 0 in34.2 MPH66 MPH

250 (WSW)

05/18/1934 F26 F 0.06 in 0.5 in39 MPH74 MPH

300 (WNW)

05/17/1940 F28 F .22 in .05 in37 MPH81 MPH

300 (WNW)

05/16/1932 F25 F .03 in 04 in22.8 MPH40 MPH

310 (NW)

05/15/1926 F20 F .05 in .4 in32.1 MPH67 MPH

330 (NNW)

05/14/1928 F17 F .2 in 2 in19.1 MPH57 MPH

100 (E)

05/13/1928 F19 F .07 in 0.9 in34.6 MPH67 MPH

100 (E)

05/12/1931 F17 F 0 in 0 in20.5 MPH47 MPH

330 (NNW)

05/11/1932 F18 F .1 in 0 in53.6 MPH84 MPH

300 (WNW)

05/10/1944 F27 F .85 in 0 in50.1 MPH88 MPH

220 (SW)

05/09/1942 F20 F .04 in 0 in18.6 MPH44 MPH

190 (S)

05/08/1927 F18 F 0 in 0 in38.3 MPH65 MPH

330 (NNW)

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 12/19/2018 at 7:09 AM.

Frank Carus
USDA Forest Service
White Mountain National Forest