Avalanche Forecast for Monday, February 18, 2019

This forecast was published 02/18/2019 at 6:58 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

Slabs that formed late last week into Saturday remain possible to human trigger today with the greatest likelihood being for small avalanches in softer wind drifted snow. Large avalanches in firmer wind slab are not yet ruled out. A small skier triggered avalanche on a low consequence terrain feature yesterday is a pertinent example what you might find today. Check this out on our observations page and thanks for this and similar observations. Consider the consequences of either a small or large avalanche in terrain you choose today, and realize that low visibility might affect your ability to assess terrain. All forecast areas have MODERATE avalanche danger.

2019-2-18_printable_pdf

Danger Rating by Zone

Mountain Weather

Clear skies and light to moderate wind yesterday gave way to clouds overnight. Snow began falling early this morning, with 1-2” forecast for today. Wind should remain light through the day, shifting NW and increasing this evening as snowfall tapers off. The current summit temperature of 7F should hold through the day. Overnight, temperatures will drop towards -10F by tomorrow morning as cloud cover decreases and NW wind approaches 70 mph with stronger gusts. Tomorrow should bring mostly clear skies with summit temperatures in the single digits F below 0 and continued NW wind around 70 mph.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs on many aspects, formed late last week on varied wind speed and direction, have generally become stubborn to a human trigger. You’re more likely to trigger an avalanche in softer pockets where your skis or boots sink into the slab. The possibility of a large avalanche does remain, particularly where the snow has a hollow sound. New snow on increasing NW wind may build new reactive but small slabs by late today or tonight.

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

The robust crust that was widespread in our terrain has mostly been covered by wind slabs formed since Wednesday at middle and upper elevations. The layered slabs above the crust formed on multiple periods of westerly and southerly wind and as recently as Saturday, with small new slabs likely to develop late today. As of yesterday, surface slabs were generally firm (1F +/-) and supportable under skis, with softer pockets of greater ski penetration and certainly boot penetration existing also. We suspect these softer pockets could behave similarly to the small skier triggered avalanche in the Ammonoosuc Ravine yesterday. A firm over soft structure has been identified in the slabs formed above the crust, keeping large avalanches a relevant though less likely concern. Keep this possibility as well as the spatial variability inherent to wind slabs in mind as you make snowpack observations today.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.

Please join us for an evening of avalanche awareness at Flatbread Company in North Conway this coming Thursday!

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 02/18/2019 at 6:58 AM.

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