Avalanche Forecast for Sunday, December 23, 2018

This forecast was published 12/23/2018 at 7:08 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

New snow that fell at the tail end of the rain event, combined with extreme winds, has formed isolated areas of wind slab that should be small and easy to avoid by staying on wind scoured slopes. All elevations and aspects have LOW avalanche danger today. In all locations, long, sliding falls will create equal, if not greater, hazard for the day. Ice dams and undermined snow will add to the list of objective hazards that are present in the range today.

2018-12-23 Printable PDF

Danger Rating by Zone

Mountain Weather

The rain event over the past few days introduced close to 3” of rain to our snowpack. Temperatures fell below freezing late Saturday morning, continuing to drop to a current 1F on the summit. Before precipitation shut off, 2.1” of snow fell on the summit, about ¾” at Grey Knob, and a trace at Hermit Lake. This snow arrived on 40 mph west winds that shifted WNW and increased to 80+ mph for the remainder of the day. High pressure across the region today will create clear skies, decreasing wind speeds from NW 74 mph at 6am to around 30 mph by dark, and temperatures in the teens F. Clouds will develop late in the day with a chance of snow, though accumulations should be minimal. The next round of high pressure will move in Monday afternoon, setting up a dry pattern for the holiday week.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slab that formed yesterday afternoon is likely small, isolated, and stubborn to a trigger by skiers and climbers due to high wind speeds. The largest and thickest areas of wind slab can be found in the direct lee of WNW wind with the largest fetch, such as low in the Headwall area of Tuckerman. These wind slabs should be easily discernible from other refrozen, scoured surfaces.

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

Following a snowy November and cold start to December, the inevitable reset button was hit for our snowpack this past week. Three inches of rain with warm temperatures saturated the upper part of our snowpack and was followed by plummeting temperatures, creating a hard and fast sliding surface. While the avalanche problem exists today, it is isolated in nature and other objective hazards deserve as much respect. Long, sliding falls will be possible on any slope but flat surfaces: use crampons and an ice axe properly. Ice dams will form when a flash freeze follows rain events. Climbers should be particularly aware of this on all aspects and elevations. Holes in the snow due to undermining were visible yesterday in many gullies and are a good indication of thin spots in the snowpack.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch, though expect ice, the occasional rock, and open waterbars to add to the challenge.

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 12/23/2018 at 7:08 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest