Avalanche Forecast for Tuesday, December 18, 2018

This forecast was published 12/18/2018 at 7:02 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

A few inches of new snow and sustained NW wind in the 60-80 mph range have made new wind slabs the primary avalanche concern for today. It’s worth remembering that wind can build slabs much thicker than our recent small snow totals. Wind will continue to affect snow on the ground through this forecast period, and limited visibility will make identifying features of concern a challenge. The Headwall area of Tuckerman Ravine has CONSIDERABLE avalanche danger with natural avalanches that threaten the floor of the ravine remaining possible. All other forecast areas have MODERATE avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully.

2018-12-18 Printable PDF

Danger Rating by Zone

Mountain Weather

Sustained NW wind around 60 mph, with several hours over 70 mph, since yesterday evening has affected our recent snowfall. Storm snow totals as of this morning are 2.5” at the Hermit Lake snow plot, 3.5” at the Grey Knob snow plot, and just over 3” on the summit. Expect NW wind to continue through today and potentially increase from the current 60 mph on the summit to just shy of the century mark. Snowfall is tapering off, though we may receive another trace to 2”. Temperatures have dropped to below 0F on the higher summits and should only increase a few degrees today. Cloud cover is likely to reduce visibility though ultimately give way to mostly clear skies by tomorrow. Forecasts indicate that temperatures should rise slightly tomorrow, with decreasing wind and no precipitation.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

New wind slab that will vary in size and likelihood of triggering is our primary avalanche problem. It’s likely you’ll find relatively large areas of firm and stubborn wind slab, with smaller pockets that are softer and more reactive. This avalanche problem should be confined to the eastern half of the compass rose in alpine terrain, with scouring limiting concerns on many westerly aspects and minimal new snow at lower elevations.

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

Sustained NW wind which continues today is the primary driver of conditions in our upper snowpack, transporting the snowfall of the past 36 hours as well as older snow on the ground. A lack of visibility has not allowed visual observations to determine distribution of both wind deposition and scouring. We expect that lee areas hold relatively firm and stubborn new wind slabs of varying size. Areas more exposed to wind, which includes both westerly aspects and some upper start zones on easterly aspects, are likely scoured of soft snow. Pockets of softer and more reactive new wind slab should also exist as a result of cross loading and wind edy affects. Beneath any of these new slabs and also present at the surface where scouring has occurred will be a mixed bag including firm old wind slab and the Dec. 3rd crust. It’s worth noting that facets have been observed around this crust, though we still don’t expect them to be a player in much of our terrain due to lack of propagation potential in the slabs above.

Additional Concerns

Ski trails in the Pinkham Notch area remain snow covered.

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
05/18/1934 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)

05/07/1939 F26 F .54 in 0 in40 MPH66 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 12/18/2018 at 7:02 AM.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest